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Revised July 2014

Investigation of Mixed Metal
Polyoxometalates as
Precursors to Niobate and
Tantalate Materials
Written and Submitted by
Akina Marissa Carey
In fulfillment for the degree of
Master of Science (by Research) in Chemistry
University of Warwick, Department of Chemistry
September 2014

Table of Contents
1.1 POLYOXOMETALATE CHEMISTRY .........................................................................................3
1.1.1 Historical Background .........................................................................................3
1.1.2 Structural Background.........................................................................................4
1.1.3 Lindqvist Structure ..............................................................................................6
1.2 PEROVSKITES.....................................................................................................................7
1.2.2 Structural Background.........................................................................................7
1.3 MICROSCOPY OF CARBON NANOTUBES ...............................................................................9
1.3.2 Structural Background.......................................................................................10
3.1 MATERIALS.......................................................................................................................14
3.2 INSTRUMENTATION............................................................................................................14
3.2.1 Infrared Spectroscopy.......................................................................................14
3.2.2 Single Crystal X-ray Diffraction .........................................................................14
3.2.3 Powder X-ray Diffraction ...................................................................................14
3.2.4 High-Resolution Powder X-ray Diffraction ........................................................15
List of Figures................................................................................................................ i
List of Tables ................................................................................................................iii
Acknowledgements.......................................................................................................iii
Declaration ...................................................................................................................iv
Abstract ........................................................................................................................ v
Abbreviations................................................................................................................ 1
1 Introduction................................................................................................................ 3
2 Motivation and Objective.......................................................................................... 12
3 Experimental Procedure .......................................................................................... 14

3.2.5 Thermogravimetric Analysis..............................................................................15
3.2.6 High-Resolution Transmission Electron Microscopy ........................................15
3.3 PEROXIDE SYNTHESIS.......................................................................................................15
K3Nb(O2)4 ...................................................................................................................15
K3Ta(O2)4....................................................................................................................16
3.4 POM SYNTHESIS..............................................................................................................16
K7Na[Nb6O19] • 10 H2O and K8[Nb6O19] • x H2O.........................................................16
K7Na[Nb4Ta2O19] • 13 H2O .........................................................................................16
K7Na[Nb3Ta3O19] • 12 H2O and K8[Nb3Ta3O19] • x H2O..............................................16
K7Na[Nb2Ta4O19] • 11 H2O .........................................................................................17
K7Na[Ta6O19] • 12 H2O ..............................................................................................17
TMA salt of [Ta6O19]
8-
• x H2O ....................................................................................17
TBA salt of [Nb2W4O19]
4-
• x H2O.................................................................................18
3.5 PEROVSKITE SYNTHESIS ...................................................................................................18
KNbO3 and NaNbO3 using Chlorides.........................................................................18
KNbO3 and NaNbO3 using [Nb6O19]
8-
.........................................................................18
KNb0.5Ta0.5O3 and NaNb0.5Ta0.5O3 using Chlorides ...................................................19
KNb0.5Ta0.5O3 and NaNb0.5Ta0.5O3 using [Nb3Ta3O19]
8-
..............................................19
KNb0.33Ta0.67O3 and NaNb0.33Ta0.67O3 using [Nb2Ta4O19]
8-
........................................19
KTaO3 and NaTaO3 using Chlorides..........................................................................19
KTaO3 and NaTaO3 using [Ta6O19]
8-
..........................................................................20
3.6 ATTEMPTED FILLING OF CARBON NANOTUBES ....................................................................20
K7Na[Nb4Ta2O19] • 13 H2O in DWNT .........................................................................20
TMA salt of [Ta6O19]
8-
• x H2O in DWNT ....................................................................20
4-
x H2O in DWNT ..................................................................21
4-
x H2O in SWNT ..................................................................21
4.1 K3NB(O2)4 AND K3TA(O2)4 ................................................................................................22
4.2 NIOBIUM- AND TANTALUM-CONTAINING POLYOXOMETALATE IONS .......................................24
4.3 PEROVSKITE MATERIALS ...................................................................................................31
4 Results and Discussion............................................................................................ 22

4.4 FILLING OF CARBON NANOTUBES.......................................................................................36
APPENDIX A: TABLES OF CONDUCTED EXPERIMENTS ...............................................................45
APPENDIX B: IR SPECTRA OF K3NB(O2)4 AND K3TA(O2)4; FULL AND CLOSEUP ...........................49
APPENDIX C: TGA MEASUREMENT AND COMPARISON BETWEEN K3NB(O2)4 AND K3TA(O2)4.......50
APPENDIX D: PXRD COMPARISON OF OBSERVED (A) K8[NB6O19] AND (B) K8[NB3TA3O19]...........51
APPENDIX E: BOND LENGTHS IN [NB6O19]
8-
, [TA6O19]
8-
, AND K7NA[NB4TA2O19] • 13 H2O_
SINGLE CRYSTAL.....................................................................................................................52
APPENDIX F: TGA COMPARISON BETWEEN K7NA[NB6O19] AND K7NA[TA6O19] ...........................53
APPENDIX G: TGA COMPARISON BETWEEN MIXED-METAL POMS ..............................................54
APPENDIX H: OUTLINE OF ROUTES CONSIDERED FOR PEROVSKITE SYNTHESIS...........................55
APPENDIX I: COMPARISON OF SAMPLES MADE FROM CHLORIDES AND MADE FROM POMS...........56
APPENDIX J:
93
NB SOLID-STATE NMR OF PEROVSKITE SAMPLES ...............................................60
5 Conclusion............................................................................................................... 42
6 Future Work............................................................................................................. 43
Appendix .................................................................................................................... 45
References ................................................................................................................. 61

i
List of Figures
Figure 1: Table mapping most common POM structures with their respective possible
compositions.................................................................................................................5
Figure 2: Structures of a) Lindqvist anion and b) Keggin anion found for
polyoxoniobates and polyoxotantalates ........................................................................6
Figure 3: Lindqvist anion [M6O19]8-
................................................................................7
Figure 4: Possible perovskite representations and arrangements.................................8
Figure 5: Orientations of carbon nanotubes ................................................................ 11
Figure 6: Outline of the Synthetic Chemistry Proposed for the Project........................ 13
Figure 7: PXRD patterns of (a) K3Nb(O2)4_observed, (b) K3Nb(O2)4_reported ............ 22
Figure 8: Structure of [M(O2)4]3-
,(M= Nb or Ta)........................................................... 23
Figure 9: PXRD pattern comparison for series of POMs (a) {K7Na[Nb6O19]} ............... 24
Figure 10: PXRD comparison of (a) K8[Nb6O19], (b) K7H[Nb6O19], (c) Na7H[Nb6O19], (d)
{K7Na[Nb6O19]}, (e) {K7Na[Nb4Ta2O19]}, (f) {K7Na[Nb3Ta3O19]}, (g) {K7Na[Nb2Ta4O19]},
(h) {K7Na[Ta6O19]}, (i) K8[Ta6O19], (j) K7Na[Ta6O19], (k) Na8[Ta6O19]............................. 25
Figure 11: PXRD pattern comparison for (a) K8[Nb6O19]_reported .............................. 26
Figure 12: Structure of K7Na[Nb4Ta2O19] • 13H2O determined by single crystal XRD.. 27
Figure 13: Comparison of PXRD of (a) {K7Na[Nb3Ta3O19]}, (b) simulated pattern from
single-crystal data of K7Na[Nb4Ta2O19] • 13H2O, and (c) {K7Na[Nb4Ta2O19]} ............... 30
Figure 14: HRPXRD of Potassium Perovskites........................................................... 33
Figure 15: HRPXRD of Sodium Perovskites (a) NaNbO3_chloride, (b) NaNbO3_POM
(c) NaNb0.5Ta0.5O3_chloride, (d) NaNb0.5Ta0.5O3_POM, (e) NaNb0.33Ta0.67O3_POM (f)
NaTaO3_chloride, (g) NaTaO3_POM .......................................................................... 34
Figure 16: HRTEM of {K7Na[Nb4Ta2O19]} clusters surrounding a multi-walled carbon
nanotube .................................................................................................................... 37
Figure 17: PXRD comparison of (a) TMA salt of [Ta6O19]8-
and (b) K8[Ta6O19]............. 38
Figure 18: Sequence of images showing the TMA salt of [Ta6O19]8-
degrading walls of
E. Flahaut’s DWNTs ................................................................................................... 39

ii
Figure 19: PXRD comparison of synthesized TBA-[Nb2W4O19]4-
and TMA-[Ta6O19]8-
.. 40
Figure 20: HRTEM of clusters of TBA salt of [Nb2W4O19]4-
inside double- and multi-
walled nanotubes........................................................................................................ 41
Figure 21: HRTEM of clusters and possible single ions of TBA salt of [Nb2W4O19]4-
inside single and multi-walled nanotubes.................................................................... 41

iii
List of Tables
Table 1: Crystal data for K7Na[Nb4Ta2O19] • 13H2O .................................................... 28
Table 2: Occupancy of Nb and Ta of Addendum Metal Sites in K7Na[Nb4Ta2O19] •
13H2O......................................................................................................................... 29
Table 3: Table of established niobate and tantalate perovskite space groups and lattice
parameters ................................................................................................................. 32
Table 4: Space groups and refined lattice parameters of K-perovskites...................... 34
Table 5: Space groups and lattice parameters of Na-perovskites ............................... 35
Acknowledgements
I would like to thank my supervisor, Professor Richard Walton, and supporting
supervisor, Professor Jeremy Sloan, for their continued support and motivation
throughout my project. Both professors have been wonderful role models and
exceedingly patient when explaining new material.
I am also grateful for the support and help from current members of the research group
Luke Daniels, Craig Hiley, David Burnett, Dan Cook, Matthew Breeze, and Dr. Juliana
Fonseca de Lima.
In particular, I would like to thank Luke Daniels for HRPXRD and TGA, Dr. Guy
Clarkson for single crystal XRD, Andrew Rankin from University of St. Andrews for
solid-state NMR.
I am thankful to the United States and Luxembourg governments, and NATO for
financial support.
Finally, I would like to thank my family, friends, and particularly my boyfriend for the
emotional support and encouragement during my project.

iv
Declaration
I hereby declare that this thesis is solely my work unless otherwise stated. The project
was carried out in support of the degree of MSc (by research) in Chemistry, at the
University of Warwick, Department of Chemistry. The section “Introduction,
Polyxometalates: Historical Background, Polyoxometalates: Structural Background” is
based on text in the author’s Bachelor Thesis at Jacobs University, Bremen, Germany,
submitted May 24, 2013 titled “Titanium-Containing Tungstoarsenates”.
______________________________ ___________________________
Authors Signature Date

v
Abstract
[NbxTa6-xO19]8-
with varying ratios of niobium and tantalum and countercations were
synthesized. The samples were characterized by powder X-ray diffraction and
thermogravimetric analysis. K7Na[Nb3Ta3O19] • 12H2O produced crystals which were
analysed using single-crystal X-ray diffraction. The structure gave a formula of
K7Na[Nb4Ta2O19]. When comparing the simulated powder pattern of K7Na[Nb4Ta2O19]
and comparing it to those of K7Na[Nb3Ta3O19] • 12H2O and K7Na[Nb4Ta2O19] • 13H2O,
none equated, inferring the batch samples were a mixture of various ratios of
K7Na[NbxTa6-xO19].
Perovskites synthesised by hydrothermally reacting the polyoxometalates, NbCl5, and
TaCl5 were investigated and analysed using high-resolution X-ray diffraction
(HRPXRD). It was observed that for the potassium perovskites, KNbO3 using the POM
was less crystalline, and KNb0.5Ta0.5O3 from the chlorides produce a phase impure
sample. All sodium perovskites were orthorhombic as expected. Preliminary solid-state
NMR showed both samples of NaNbO3 have comparatively similar Nb environments, a
decrease in intensities for decreasing niobium content for the potassium niobium-
tantalum samples, and a significant difference in location and peak width between both
samples of KNbO3.
When inserting K7Na[Nb4Ta2O19] into double-walled nanotubes, the anions were only
visible surrounding the nanotubes. The countercation was substituted to
tetrabutylammonium and [Ta6O19]8-
was used, this resulted in the destruction of the
carbon walls. This could be due to the high charge of the anion as well as the electron-
beam-induced reaction between Ta and the carbon walls. TBA-[Nb2W4O19]4-
was used
instead resulting in the insertion of [Nb2W4O19]4-
clusters. To decrease the nanotube
diameter, single-walled nanotubes with a diameter of 1.2-1.7 nm were used, resulting
in smaller clusters with possible single-ion-like structures being observed.

1
Abbreviations
{K7Na[Nb6O19]}: K7Na[Nb6O19] • 10 H2O
{K7Na[Nb4Ta2O19]}: K7Na[Nb4Ta2O19] • 13 H2O
{K7Na[Ta6O19]}: K7Na[Ta6O19] • 12 H2O
POM: Polyoxometalate
CNT: Carbon nanotubes
SWNT: Single-walled nanotube
DWNT: Double-walled nanotube
TEM: Transmission Electron Microscopy
HRTEM: High-Resolution Transmission Electron Microscopy
EDAX: Energy-Dispersive X-ray Analysis
SEM: Scanning Electron Microscopy
XRD: X-ray Diffraction
PXRD: Powder X-ray Diffraction
HRPXRD: High-resolution powder x-ray diffraction
EDXRD: Energy-DispersiveX-ray Diffraction
IR: Infrared Spectroscopy
TGA: Thermogravimetric Analysis
Temp: Temperature
RT: Room temperature

2
A.U.: arbitrary unit
NI: NanoIntegris
SWeNT: SouthWest Nanotubes
MeOH: Methanol
EtOH: Ethanol
TMAOH: Tetramethylammonium hydroxide
TEAOH: Tetraethylammonium hydroxide
TPAOH: Tetrapropylammonium hydroxide
TBAOH: Tetrabutylammonium hydroxide

3
1 Introduction
1.1 Polyoxometalate Chemistry
1.1.1 Historical Background
Polyoxometalates (POMs) are a subset of metal oxide clusters, generally classified as
polyanions, and have a range of physical and structural properties. (1)
The first POM
was synthesized by Swedish chemist, Jöns Jakob Berzelius, in 1826. (2)
He discovered
that when adding ammonium molybdate to phosphoric acid, a yellow precipitate formed
leading to the now known ammonium 12-molybdophosphate, (NH4)3PMo12O40. (3)
Its
structure was investigated in 1848 by Svanberg and Struve. The next significant step
came in 1862 when Marignac discovered tungstosilicic acids and their corresponding
salts (4)
leading to Werner creating his coordination theory to explain the compositions
and structures of heteropolyanions. (5)
His understanding and theory resulted in him
receiving a Nobel Prize in Chemistry in 1913, later becoming the foundation for modern
coordination chemistry. Werner’s achievements were later advanced by Miolati and
Pizzighelli in 1908 and even further by Rosenheim. From this, the Miolati-Rosenheim
theory was introduced stating that heteropolyacids were based on 6-coordinate
heteroatoms with a MO4
2-
or M2O7
2-
anions as ligands or bridging groups.
This was criticized in 1929 by Pauling when he recognized that the ionic radii of Mo6+
and W6+
were suitable for an octahedral coordination by corner oxygen. Pauling
suggested that each of the MO6 (M = Mo, W) encapsulated a central tetrahedron, XO4
(X = heteroatom), for a 12:1 complex. This gave a more accurate explanation for the
observed basicity than what would be observed using the Miolati-Rosenheim theory.
Pauling’s criticism was later corrected by Keggin when he revealed the structure of the
polyanion H3[PW12O40] • 5H2O by use of XRD. The crystal structure indicated that the
octahedral structure by WO6 was actually due to the linkage of both corner- and edge-
sharing between octahedra. (6)
Reports of isomorphous complexes of the “Keggin ion”

4
followed this correction, resulting in the reports of the structures of Evans-Anderson,
Lindqvist, and Wells-Dawson anions. (5)
1.1.2 Structural Background
POMs are commonly synthesized using aqueous solutions, resulting in the
condensation of octahedral MO6 units which are linked via three types of sharing; edge,
corner, and, less frequently, face. (7)
POMs are usually composed of early transition
metal addendum atoms in MO6 octahedra (M (addendum) = W6+
,Mo6+
, V5+
, Nb5+
,Ta5+
)
with heteroatoms in the XO4 tetrahedra (X = P, Si, etc). Since an octahedral
coordination is formed by the metal atom, the maximum coordination number of these
atoms needs to be six to fulfil the structural requirements. In addition to the
coordination, the early transition metal atoms which can be used in such structures are
limited based on their ionic radius and charge, and the ability to accept pπ electrons
from oxygen to form stable dπ-pπ M-O bonds. This, therefore, reduces the number of
metal atoms which can be used. There are no such restrictions of the heteroatom. (5)
POMs are separated into two sub-categories: isopolyanions and heteropolyanions.
Isopolyanions consist only of the addenda atoms, M, in its highest oxidation state and
bridged via oxygen, while, heteropolyanions contain a heteroatom, X.
These polyanions are formulated as follows:
Isopolyanions: [MmOy]p-
M = Mo, W, V, Nb, Ta
Heteropolyanions: [XxMnOy]q-
X = P, Si (x ≤ m)
Figure 1 shows an outline of the commonly known POMs in all possible structural
orientations.

5
Figure 1: Table mapping most common POM structures with their respective
possible compositions taken from Long, D.-L., Tsunashima, R. and Cronin, L.
Chem. Int. Ed. 49. 2010. 1736–1758. (1)
If niobium or tantalum are the addendum atom, the anion is referred to as being
polyoxoniobates and polyoxotantalates, respectively. These isopolyanions have not
been highly investigated compared to other POMs, and are less evolved due to the
ions being stable only in basic solutions. Polyoxoniobates have recently been
developed in the form of a heteropolyanion and isolated as a Keggin structure. (8)
The
two structures of polyoxoniobates and tantalates, which can be observed, are shown in
Figure 2.
Since this thesis focuses on the synthesis, characterization, and reaction of niobium,
tantalum, and tungsten containing Lindqvist isopolyanions, the structure of the
Lindqvist anion will be discussed further below.

6
Figure 2: Structures of a) Lindqvist anion and b) Keggin anion found for
polyoxoniobates and polyoxotantalates
1.1.3 Lindqvist Structure
The Lindqvist anion, [M6O19]8-
, is named after its discoverer I. Lindqvist. The structure
was first realized in 1952 when fusing Nb2O5 with excess metal hydroxides or
carbonates and then dissolving the melt in water. This resulted in crystals of
Na7HNb6O19 • 16H2O. (9)
In parallel to this discovery, Lindqvist and Aronsson
characterized the structure of K8Ta6O19 • 16H2O. (10)
Since these findings, very little
have been investigated regarding the Lindqvist anions in comparison to other POMs. It
is also possible to synthesize these structures via a solution route, and not only
hydrothermally. (11)
The Lindqvist anion is a super-octahedron containing 6 edge-sharing MO6 octahedra.
Each octahedral metal is bonded to the central oxygen, resulting in 6 terminal oxygens
(Figure 3), which can, and have been, used for introducing functional ligands allowing
for greater control over the POM.
-MO6 octahedron -Heteroatom

7
Figure 3: Lindqvist anion [M6O19]8-
Despite the lack of interest in this isopolyanion, they do have appealing physical
properties. For example, they have high overall charges and very basic oxygen
surfaces which could be used for further use as building blocks for extended solid
structures. (1)
1.2 Perovskites
The perovskite mineral (CaTiO3) is found naturally around the world and was first
discovered by Gustav Rose in 1839 in the Ural Mountains. He then named it after the
Russian mineralogist, Count Lev Aleksevich von Perovski. (12)
Unfortunately, research
on perovskites did not make a significant increase until the mid-1940s in which the first
crystal structure a CaTiO3 type orthorhombic perovskite was discovered and reported
by Helen Dick in 1945. Interest toward solid-state research, focusing on ferroelectric
materials, is attributed to this increase. Since this increase, applications of perovskite
materials have ranged from use in sensors and memory devices to superconductors
and solid oxide fuel cells. (13)
The perovskite structure has an ideal formula of ABX3 with a space group of Pm̅m.
The A-site cations are larger in size than the B-site cations, however, the latter are of
M
O

8
similar size to the X-site anions. In this ideal structure, the A-cations are bound by
twelve anions in the cubo-octahedral coordination while the B-cations by six anions in
the octahedral coordination, (Figure 4a). The structure is best represented by SrTiO3 as
it exhibits the closest resemblance to the ideal. (14)
The standard cubic perovskite structure has a Pm̅m space group, and with 2 common
representations of the unit cell. In the cubic A-cell structure, the B-cations are located
at each of the corners, A-cation in the centre of the cube, and X-anions at the edge-
centred position, (Figure 4b1).This differs from the cubic B-cell structure where the A-
cations are at each corner, B-cation in the centre of the cube, and X-anions at the face-
centred positions, (Figure 4b2). (13)
Figure 4: Possible perovskite representations and arrangements
a) Ideal structure b1) Cubic A-cell structure b2) Cubic B-cell
c) Orthorhombic structure
B
X
A

9
In order to achieve this aforementioned arrangement, the relative size of the A-cation,
B-cation, and X-anion must be of a specific ratio in relation to each other. If this ratio is
not achieved, other orientations can occur. Most notably, the CaTiO3 mineral exhibits
an orthorhombic structure, with a space group of Pnma or Pbnm, (Figure 4c). In this
structure the octahedra at the corners of the cubic structure become tilted, but are still
corner-sharing. This occurs when the A-cation is too small within the polyhedral
framework causing the centre-vertical edge X-anions to compress inwards. (14)
Other structures have been reported such as tetragonal, rhombohedral, and various
distortions of these. As this study focused on MNbO3, MTaO3, and MNbxTa1-xO3 (M=
Na or K), only cubic and orthorhombic structures have been shown since these are the
crystal symmetries expected for these materials.
1.3 Microscopy of Carbon Nanotubes
Microscopes have been in existence since the late 1500s however with the introduction
of the transmission electron microscopy in 1931 by Ernst Ruska and Max Knoll began
a surge of advancements. The scanning electron microscope (SEM) was introduced in
1942 and since, the improvements of these microscopes have improved dramatically.
(15)
Microscopy was not used to view nanotubes until 1991 when Sumio Iijima made and
imaged the first carbon nanotubes using transmission electron microscopy. This was
done when synthesising fullerenes by an arc-discharge evaporation method. (16)
Carbon
nanotubes (CNTs) have been of increase interest for their applications toward energy
storage, sensors, and encapsulation. (17)
Filling of nanotubes have varied significantly since the 1990s when the research was
dominated by inserting fullerenes into single- and multi-walled CNTs resulting in
“peapod” structures. (18)
More recently, CNTs have been filled with various metals,

10
alloys, ions and clusters. For example, polymeric iodine chains in one-dimensional
crystal structures, polyhedral chains of lanthanide trihalides, as well as HgTe has been
observed in single- and/or double-walled carbon nanotubes (SWNTs or DWNTs). (19) (20)
In addition to this, POM ions have been observed in DWNTs since 2008 when Sloan
and co-workers reported encapsulating polyoxotungstates using high-resolution
transmission electron microscopy. (19) (21) (22)
CNTs are tubes several microns in length consisting of single, double, or multiple walls
made of carbon atoms. They are synthesized by arc discharge and laser ablation, and
chemical vapour deposition (thermal and plasma-enhanced). These methods however
can leave residue, catalyst particles, and contamination behind so a cleansing
preparation should be considered before use. (17)
Due to the lack of complete control
over the formation of the nanotubes, each sample will have a small percentage of
nanotubes with various number of walls. For example, if a single-walled nanotube
sample was observed, there would be a small presence of double- and multi-walled
nanotubes within the sample.
CNTs are generally seen as hollow cylinders which are formed by rolling graphene
sheets. With this comes curvature resulting in a rehybridization of the σ bonds which
have now been pushed slightly outwards. This causes the π-orbitals to become more
delocalised, therefore making the tubes mechanically stronger, more conductive
thermally and electrically, and more chemically active. Due to the hybridisation of
carbon atoms, the preferred orientation would be in a hexagonal structure, but at the
ends of the tubes this cannot occur resulting in a single pentagon. This does cause
defects in the overall structure as the more incorporation of pentagons and heptagons,
the more likely the tube will be bent, helical, or capped. If a tube has more than one
layer of carbons stacked over each other, then these are named double or multi-walled
tubes. (17)

11
CNTs can also have different orientations, such as zig-zag, armchair, and chiral. This is
done by rolling the graphite sheet in different directions, (Figure 5).
Figure 5: Orientations of carbon nanotubes taken from Galano, A. Nanoscale
2(3).2010. 373-80. (23)
In addition to the various orientations of CNTs, each type can vary in length and
diameter. Typically, single-walled nanotubes have a diameter of <2 nm, while double
and multi-walled nanotubes have an average diameter of 1-4 nm and >3 nm,
respectively. The range of diameters is due to the different methods of synthesizing
CNTs and control over the exact growth have not yet been identified with great
accuracy.

12
2 Motivation and Objective
The interest in in perovskite materials have dramatically increased in the last 50 years
with applications towards sensors and fuel cells. (13)
In 2008, the Walton research group
published findings of a Lindqvist-structured polyoxoniobate intermediate in the
hydrothermal synthesis of sodium niobates using Nb2O5. By using in situ energy-
dispersive X-ray diffraction (EDXRD), the group could observe its transient appearance
during the reaction. (24)
This observation was used in the work described here to see if it was possible to
control the perovskite by starting from the POM in synthesis. The aim of this study was
to synthesize a mixed niobium-tantalum containing POM in the Lindqvist structure, and
further convert it to mixed niobium-tantalum perovskites. Niobate and tantalate
perovskites have ferroelectric properties and there is a need to make new mixed oxides
with controlled composition. Usually high temperatures are used in the synthesis and
solution hydrothermal methods could provide a way of controlling the composition and
crystal form of the product.
Simultaneous to this work, the group led by Jeremy Sloan published a paper on
encapsulating Lindqvist ions containing tungsten inside of carbon nanotubes. A click-
move-click movement was observed within the nanotubes. (19) (21) (22)
The work in this
thesis continues the finding by attempting to insert mixed-metal Lindqvist ions and
observing the position of each metal atom within the ion as well as the ion inside the
nanotube. The outline of the synthetic chemistry in the project is shown in Figure 6.

13
Chlorides Peroxides POMs Perovskites POMs in NTs
Figure 6: Outline of the Synthetic Chemistry Proposed for the Project
[NbxTa6-xO19]8-
In: H2O
H2O/EtOH
EtOH
DWNT
[NbxW6-xO19](2+x)-
In: EtOH
DWNT
SWNT
NbCl5
[Nb6O19]8-
KNbO3
K3Nb(O2)4
[NbxTa6-xO19]8-
KNbxTa1-xO3
K3NbxTa1-x(O2)4
TaCl5
[Ta6O19]8-
KTaO3
K3Ta(O2)4

14
3 Experimental Procedure
See Appendix A for full description of reactions done
3.1 Materials
The following chemicals were obtained from Sigma Aldrich; Na2WO4 • 2H2O (99%),
HNaSO3 (40%), TBAOH • 30H2O (98.0%), carbon nanotube, double walled (≤10%
Metal Oxide), carbon nanotube, single-walled, purified (>95% carbon, <1% catalyst,
supplied by NanoIntegris). NbCl5 (99%) was supplied by Alfa Aesar, TaCl5 (99.90%) by
AcrosOrganics, carbon nanotube, double-walled by Emmanuel Flahaut, carbon
nanotube, single-walled by SWeNT, and lacey and holey Cu support grids (carbon-
coated, 3.05 mm) by Agar Scientific.
3.2 Instrumentation
3.2.1 Infrared Spectroscopy
Infrared spectroscopy of powder samples was done on the powder samples using a
PerkinElmer Spectrum100 FT-IR instrument.
3.2.2 Single Crystal X-ray Diffraction
Single-crystal X-ray diffraction was used on a Gemini R diffractometer from Oxford
Diffraction equipped with an Oxford Cryosystems Cobra. The structures were solved by
direct methods using SHELXS and refined using SHELXL 97. This was performed by
Dr. Guy Clarkson.
3.2.3 Powder X-ray Diffraction
A Siemens D5000 diffractometer equipped with Cu Kα radiation was used for the
preliminary characterisation. The data were collected over a range of 2θ, 8-60°, using a
step size of 0.02° and 1.1 second/step measurement.

15
3.2.4 High-Resolution Powder X-ray Diffraction
High-resolution data were collected using a Panalytical X’Pert Pro MPD that was
equipped with a monochromatic Cu Kα1 radiation using a PIXcel solid state detector.
The data were collected over a range of 2θ, 20-100°, and spun at a rate of 4
revolutions/second.
3.2.5 Thermogravimetric Analysis
Thermal analysis was done using a Mettler Toledo Systems TGA/DSC 1 instrument.
Alumina crucibles with a constant flow of N2 at 50 mL/minute were used as well as the
temperature ranging from room temperature to 1000°C at a heating rate of 10°C
/minute.
3.2.6 High-Resolution Transmission Electron Microscopy
A JEM-ARM 200F microscope (at 80 kV) equipped with a CEOS aberration correction
and a Gatan SC1000 ORIUS camera with a 4008 2672 pixel charge-coupled device
(CCD) was used. Dispersions of POM and SWNT/DWNT nanocomposites were drop-
casted onto 3.05 mm Cu lacey or holey carbon-coated support grids.
3.3 Peroxide Synthesis
The following syntheses are based a publication by Nyman and co-workers. (11)
K3Nb(O2)4
NbCl5 (6.60 g, 24.4 mmol) was added to 75 mL 30% H2O2 in an ice bath with moderate
stirring. KOH (65 mL, 4 M) added to solution in 1mL aliquots. 150 mL of MeOH was
added and allowed to cool to 5-8°C. A further 100 mL of MeOH was added and allowed
to stir for 5 minutes. The product was filtered, washed with 200 mL MeOH, collected
and air dried at room temperature.

16
K3Ta(O2)4
TaCl5 (8.75 g, 24.4 mmol) was added to 75 mL 30% H2O2 in an ice bath with moderate
stirring. KOH (65 mL, 4 M) added to solution in 1 mL aliquots. 150 mL of MeOH was
added and allowed to cool to 5-8°C. A further 100 mL of MeOH was added and allowed
to stir for 5 minutes. The product was filtered, washed with 200 mL MeOH, collected
and air dried at room temperature.
3.4 POM Synthesis
The following syntheses are based on a publication by Nyman and co-workers (11)
K7Na[Nb6O19] • 10 H2O and K8[Nb6O19] • x H2O
K3Nb(O2)4 (3.18 g, 9.40 mmol), KOH (3.82 g, 68.1 mmol), and Na3VO4 (0.110 g, 0.598
mmol) was added to 15 mL H2O. The suspension was refluxed for 2 hours at 115°C.
The solution was then filtered, allowed to evaporate slowly in air at room temperature,
periodically collecting the product as it crystallized. To synthesize K8[Nb6O19], Na3VO4
was substituted with K3VO4 (0.137 g, 0.590 mmol).
{K7Na[Nb6O19]} will be used to reference this product in future sections.
K7Na[Nb4Ta2O19] • 13 H2O
K3Nb(O2)4 (2.12 g, 6.27 mmol), K3Ta(O2)4 (1.34 g, 3.14 mmol), KOH (3.82 g, 68.1
mmol), and Na3VO4 (0.110 g, 0.598 mmol) was added to 15 mL H2O. The suspension
was refluxed for 2 hours at 115°C. The solution was then filtered, allowed to evaporate
slowly in air at room temperature, periodically collecting the product as it crystallized.
{K7Na[Nb4Ta2O19]} will be used to reference this product in future sections.
K7Na[Nb3Ta3O19] • 12 H2O and K8[Nb3Ta3O19] • x H2O
K3Nb(O2)4 (1.59 g, 4.70 mmol), K3Ta(O2)4 (2.00 g, 4.69 mmol), KOH (3.82 g,
68.1 mmol), and Na3VO4 (0.110 g, 0.598 mmol) was added to 15 mL H2O. The
suspension was refluxed for 2 hours at 115°C. The solution was then filtered, allowed

17
to evaporate slowly in air at room temperature, periodically collecting the product as it
crystallized. To synthesize K8[Nb3Ta3O19], Na3VO4 was substituted with K3VO4 (0.137
g, 0.590 mmol).
K7Na[Nb2Ta4O19] • 11 H2O
K3Nb(O2)4 (1.06 g, 3.13 mmol), K3Ta(O2)4 (2.67 g, 6.26 mmol), KOH (3.82 g, 68.1
mmol), and Na3VO4 (0.110 g, 0598 mmol) was added to 15 mL H2O. The suspension
was refluxed for 2 hours at 115°C. The solution was then filtered, allowed to evaporate
slowly in air at room temperature, periodically collecting the product as it crystallized.
K7Na[Ta6O19] • 12 H2O
K3Ta(O2)4 (4.00 g, 9.38 mmol), KOH (3.82 g, 68.1 mmol), and Na3VO4 (0.110 g, 0.598
mmol) was added to 15 mL H2O. The suspension was refluxed for 2 hours at 115°C.
The solution was then filtered, allowed to evaporate slowly in air at room temperature,
periodically collecting the product as it crystallized.
{K7Na[Ta6O19]} will be used to reference this product in future sections.
TMA salt of [Ta6O19]8-
• x H2O
K3Ta(O2)4 (2.00 g, 4.69 mmol), TMAOH (6.16 g, 67.6 mmol), and Na3VO4 (0.0550 g,
0.299 mmol) was added to 15 mL H2O. The suspension was refluxed for 2 hours at
115°C. The solution was then filtered, allowed to evaporate slowly in air at room
temperature, periodically collecting the product as it crystallized.

18
TBA salt of [Nb2W4O19]4-
• x H2O
The following syntheses are based on a publication by Dabbabi and Boyer. (25)
[Nb6O19]8-
(10 mL, 0.04 M) solution was pre-heated and added to Na2WO4 • 2H2O (10
mL, 0.5 M) and H2O2 (0.11 mL, 0.5 M). The mixture was acidified to pH 5.5 using 0.5
mL conc. Acetic Acid, and refluxed for 2 hours at 80°C. After 2 hours, 1 mL NaHSO3
was added and solution allowed to cool. Once cooled, TBAOH (1.50 g, 1.87 mmol) was
added, and resulting solution filtered. 100 mL EtOH was added and product filtered,
collected and dried in air at room temperature.
3.5 Perovskite Synthesis
KNbO3 and NaNbO3 using Chlorides
NbCl5 (500 mg, 1.85 mmol) and 12 mL 20 M KOH were added and stirred together in
an autoclave with inner volume of ~20 mL. After 5 minutes of stirring, the autoclave
was placed in an oven at 240°C for 24 hours. After 24 hours, the autoclave was
removed from the oven and left to cool to ambient temperature. Once cooled, the
product was filtered, washed generously with H2O, collected and air dried at room
temperature. For NaNbO3, KOH was replaced with 12 mL 20 M NaOH and left in oven
for 48 hours.
KNbO3 and NaNbO3 using [Nb6O19]8-
500 mg [Nb6O19]8-
and 12 mL 20 M KOH were added and stirred together in an
autoclave with inner volume of ~20 mL. After 5 minutes of stirring, the autoclave was
placed in an oven at 240°C for 5 days. After 5 days, the autoclave was removed from
the oven and left to cool to ambient temperature. Once cooled, the product was filtered,
washed generously with H2O, collected and air dried at room temperature. For
NaNbO3, KOH was replaced with 12 mL 20 M NaOH.

19
KNb0.5Ta0.5O3 and NaNb0.5Ta0.5O3 using Chlorides
NbCl5 (100 mg, 0.370 mmol), TaCl5 (132 mg, 0.368 mmol), and 12 mL 20 M KOH were
added and stirred together in an autoclave with inner volume of ~20 mL. After 5
minutes of stirring, the autoclave was placed in an oven at 240°C for 24 hours. After 24
hours, the autoclave was removed from the oven and left to cool to ambient
temperature. Once cooled, the product was filtered, washed generously with H2O,
collected and air dried at room temperature. For NaNb0.5Ta0.5O3, KOH was replaced
with 12 mL 20M NaOH and left in the oven for 48 hours.
KNb0.5Ta0.5O3 and NaNb0.5Ta0.5O3 using [Nb3Ta3O19]8-
500 mg [Nb3Ta3O19]8-
placed in an oven at 240°C for 5 days. After 5 days the autoclave was removed from
NaNb0.5Ta0.5O3, KOH was replaced with 12 mL 20 M NaOH.
KNb0.33Ta0.67O3 and NaNb0.33Ta0.67O3 using [Nb2Ta4O19]8-
500 mg [Nb2Ta4O19]8-
NaNb0.33Ta0.67O3, KOH was replaced with 12 mL 20 M NaOH.
KTaO3 and NaTaO3 using Chlorides
TaCl5 (500 mg, 1.85 mmol) and 12 mL 20 M KOH were added and stirred together in
an autoclave with inner volume of ~20 mL. After 5 minutes of stirring, the autoclave
was placed in an oven at 240°C for 24 hours. After 24 hours, the autoclave was

20
removed from the oven and left to cool to ambient temperature. Once cooled, the
product was filtered, washed generously with H2O, collected and air dried at room
temperature. For NaTaO3, KOH was replaced with 12 mL 20 M NaOH and left in oven
for 48 hours.
KTaO3 and NaTaO3 using [Ta6O19]8-
500 mg [Ta6O19]8-
NaTaO3, KOH was replaced with 12 mL 20 M NaOH.
3.6 Attempted filling of Carbon Nanotubes
K7Na[Nb4Ta2O19] • 13 H2O in DWNT
70 mg {K7Na[Nb4Ta2O19]} and 1 mg DWNT (E. Flahaut) were dispersed in 5 mL EtOH
each using a sonic probe for 5 minutes (2 seconds pulse on, 2 seconds pulse off;
amplitude 20%). Each sample was dispersed separately, added together after
dispersion, and allowed to stir. The sample was then drop-casted on a lacey or holely
carbon grid.
TMA salt of [Ta6O19]8-
• x H2O in DWNT
70 mg TMA salt of [Ta6O19]8-
and 1 mg DWNT (Sigma Aldrich) were dispersed in 5 mL
EtOH each using a sonic probe for 5 minutes (2 seconds pulse on, 2 seconds pulse off;
carbon grid.

21
x H2O in DWNT
70 mg TBA salt of [Nb2W4O19]4-
and 1 mg DWNT (Sigma Aldrich) were dispersed in 5
mL EtOH each using a sonic probe for 5 minutes (2 seconds pulse on, 2 seconds pulse
off; amplitude 20%). Each sample was dispersed separately, added together after
carbon grid.
x H2O in SWNT
5 mg SWNT (Sigma Aldrich/NI) was dispersed in chloroform using a sonic probe for 10
minutes (2 seconds pulse on, 2 seconds pulse off; amplitude 20%). The nanotubes
were then lightly filtered, collected and dried. Once dried, they were put in a tube
furnace at 400°C for 24 hours.
70 mg TBA salt of [Nb2W4O19]4-
and 1 mg SWNT (heat treated) were dispersed in 5 mL
EtOH each using a sonic probe for 5 minutes (2 seconds pulse on, 2 seconds pulse off;
carbon grid.

22
4 Results and Discussion
4.1 K3Nb(O2)4 and K3Ta(O2)4
K3Nb(O2)4 and K3Ta(O2)4 were each synthesized by adding 6.61 mmol NbCl5 and
TaCl5, respectively, to 65 mL 4 M KOH solution, followed by the addition of MeOH.
Once the mixture cooled and a further addition of MeOH, the white product was
washed with MeOH, collected and air dried at room temperature.
Both K3Nb(O2)4 and K3Ta(O2)4 were then analysed using PXRD and compared to
patterns simulated from crystal structures taken from the ICSD database. This
comparison showed that the intended product was formed, (Figure 7). Peaks at ~38.3
and ~44.6 correspond to aluminium peaks from the sample holder and should be
disregarded.
Figure 7: PXRD patterns of (a) K3Nb(O2)4_observed, (b) K3Nb(O2)4_reported,
(c) K3Ta(O2)4_observed, (d) K3Ta(O2)4_reported; Al peaks labelled *
2θ / deg
Intensity(a.u.)
a
b
c
d
* *
*
*

23
K3Nb(O2)4 and K3Ta(O2)4 structurally contain the metal (Nb or Ta) surrounded by four
bidentate peroxo groups bound to the centre metal therefore forming an overall
distorted dodecahedral arrangement. The structural orientation is represented in Figure
8.
Figure 8: Structure of [M(O2)4]3-
,(M= Nb or Ta) taken from Bayot, D., and M.
Devillers. Coordination Chemistry Reviews. 250. 19-20. 2006. 2610-626.(26)
In addition to PXRD, IR spectroscopy and thermal analysis were done to observe the
stretching of the peroxo groups as well as the mass loss of decomposition respectively.
The characteristic vibrational bands for K3Nb(O2)4 and K3Ta(O2)4 are the O – O
stretching of the peroxo groups at ~812 cm-1
and ~806 cm-1
respectively.
Decomposition begins at approximately 419°C for both K3Nb(O2)4 and K3Ta(O2)4 and
exhibits a percentage weight loss of 19.9% and 15.8% respectively. These values are
comparable to the expected weight loss values of 19.0% and 15.0% respectively,
corresponding to the loss of 2 peroxy groups resulting in the following decomposition
representation: (27)
K3Nb(O2)4 (s)  K3NbO4 (s) + 2 O2 (g)
K3Ta(O2)4 (s)  K3TaO4 (s) + 2 O2 (g)
Refer to Appendix B and C for the respective IR and TGA spectra of both peroxide
compounds.
O
Nb or Ta

24
4.2 Niobium- and Tantalum-Containing Polyoxometalate Ions
All Nb- and Ta-containing POMs were synthesized by refluxing K3Nb(O2)4, K3Ta(O2)4,
or varying ratios of K3Nb(O2)4 and K3Ta(O2)4 with 68 mmol KOH and 0.3 mmol of either
Na3VO4 or K3VO4 in H2O for 2 hours. The solution was filtered and allowed to
evaporate slowly at room temperature until crystallization process is complete. The
resulting colourless crystals were collected and air dried at room temperature.
Figure 9: PXRD pattern comparison for series of POMs (a) {K7Na[Nb6O19]},
(b) {K7Na[Nb4Ta2O19]}, (c) {K7Na[Nb3Ta3O19]}, (d) {K7Na[Nb2Ta4O19]}, (e)
{K7Na[Ta6O19]}
Figure 9 is an overlay of the PXRD patterns for the K7Na salts of Nb and Ta POMs with
varying ratios. None of the patterns match, which would imply that each sample made
contained a different product, whether it contained the correct and expected ratio of Nb
and Ta or not. It is likely therefore that the size of the countercation (whether Na+
or K+
)
and the amount of crystal water affects the crystal packing and therefore the size and
a
b
c
d
e
Intensity(a.u.)
2θ / deg

25
shape of the unit cell. As these POMs have not been previously reported, therefore, in
order to confirm whether a POM had actually been synthesized various comparisons to
reported powder patterns were done, (Figure 10).
Figure 10: PXRD comparison of (a) K8[Nb6O19], (b) K7H[Nb6O19], (c) Na7H[Nb6O19], (d)
{K7Na[Nb6O19]}, (e) {K7Na[Nb4Ta2O19]}, (f) {K7Na[Nb3Ta3O19]}, (g) {K7Na[Nb2Ta4O19]},
(h) {K7Na[Ta6O19]}, (i) K8[Ta6O19], (j) K7Na[Ta6O19], (k) Na8[Ta6O19]; Observed patterns
are highlighted in yellow while reported values are not highlighted
When comparing the observed and reported patterns, similarities can be seen. For
example, the pair of peaks at approximately 9° and 9.5° are present in reported
patterns (a) K8[Nb6O19], and (i) K8[Ta6O19] as well as observed patterns (d)
{K7Na[Nb6O19]}, (f) {K7Na[Nb3Ta3O19]}, (g) {K7Na[Nb2Ta4O19]}, and (h)
{K7Na[Ta6O19]}. Peaks at approximately 10° and 11° for observed pattern (e)
{K7Na[Nb4Ta2O19]} are similar to those present in pattern (j) K7Na[Ta6O19]. Patterns
a
b
c
d
e
Intensity(a.u)
2θ / deg
f
g
h
i
j
k

26
from K8[Nb6O19], {K7Na[Nb3Ta3O19]}, and K8[Ta6O19] have been overlaid to emphasize
this comparison, (Figure 11).
Figure 11: PXRD pattern comparison for (a) K8[Nb6O19]_reported,
(b) {K7Na[Nb3Ta3O19]}_observed, (c) K8[Ta6O19]_reported
Comparable peaks are present in all synthesized samples to make a convincing
assumption that the POMs synthesized are indeed POMs. When comparing the PXRD
patterns of these POMs, an increase in the number of peaks between 20 and 60° 2θ is
observed with increasing tantalum content.
A trend is also observed after crystallisation. For structures that are niobium-rich the
crystallites are large, however with increasing tantalum content the crystallite size
decreases dramatically.
a
b
c
Intensity(a.u.)
2θ / deg

27
PXRD patterns of these POMs but containing only potassium countercations can be
found in Appendix D.
Selective single crystal XRD, (Table 1), was done on one crystal taken from a batch of
{K7Na[Nb3Ta3O19]} which gave the actual formula is K7Na[Nb4Ta2O19] rather than the
expected 1:1 Nb/Ta ratio. Each of the metal sites in the POM is occupied by both Nb
and Ta and Table 2 shows the refined site occupancies. The data also showed the
number of crystal waters resulting in a formula of K7Na[Nb4Ta2O19] • 13H2O. The 13
crystal waters present is consistent with the 13 crystal waters observed using TGA for
{K7Na[Nb4Ta2O19]} Figure 12 shows the structure of the ion.
Figure 12: Structure of K7Na[Nb4Ta2O19] • 13H2O determined by single crystal XRD
Nb/Ta
O

28
Table 1: Crystal data for K7Na[Nb4Ta2O19] • 13H2O
Formula H80Nb15.106Ta8.894O132
Crystal System Monoclinic
Space Group P21/c (14)
Cell Length (Å) a 12.6562(3) b 10.7052(2) c 24.3067 (5)
Cell Angles (°) α 90.000 β 92.100 (2) γ 90.000
Cell Volume (Å3
) 3291.03 (10)
Cell Ratios a/b= 1.1822 b/c= 0.4404 c/a= 1.9205
The bond distances for the structure are consistent with occupancy data indicating the
two sites which have slightly higher amounts of tantalum, therefore decreasing the M-O
terminal bond length. The terminal M-O bonds in the measured structure were
compared with terminal M-O in both the [Nb6O19]8-
and [Ta6O19]8-
structures to
determine the likelihood of the location of the metal atoms. See Appendix E for bond
length comparison data.

29
Table 2: Occupancy of Nb and Ta of Addendum Metal Sites in K7Na[Nb4Ta2O19] •
13H2O
Atom Site occupancy factor Atom Site occupancy factor
Nb1 0.659 Nb4 0.661
Ta1 0.341 Ta4 0.339
Nb2 0.653 Nb5 0.621
Ta2 0.347 Ta5 0.379
Nb3 0.661 Nb6 0.521
Ta3 0.339 Ta6 0.479
It should be noted that the single-crystal data are from only one crystal; this cannot be
representative for the whole sample batch. To compare the purity {K7Na[Nb3Ta3O19]}
and {K7Na[Nb4Ta2O19]}, their corresponding PXRD patterns were plotted against the
simulated pattern of the single-crystal. As shown in Figure 13, the patterns do not
match, therefore suggesting that not only is {K7Na[Nb3Ta3O19]} a mixture of various
ratios of POMs with an overall composition of {K7Na[Nb3Ta3O19]}, but it is also true for
{K7Na[Nb4Ta2O19]}. Furthermore, the different crystal packing in the PXRD-measured
samples would adjust the pattern compared to the simulated pattern from the single
crystal data. It should be noted that this is only a hypothesis and further research is
being conducted to justify this theory.

30
Figure 13: Comparison of PXRD of (a) {K7Na[Nb3Ta3O19]}, (b) simulated pattern from
single-crystal data of K7Na[Nb4Ta2O19] • 13H2O, and (c) {K7Na[Nb4Ta2O19]}
TGA was performed on all Nb and/or Ta containing POMs and can be seen in
Appendix F and G. It was observed that for {K7Na[Nb6O19]} and {K7Na[Nb4Ta2O19]}
there are two stages of water loss, suggesting they are two types of water molecules
within the crystal structure. The following are the resulting formula including waters of
crystallisation as well as their corresponding percentage mass loss: K7Na[Nb6O19] •
10H2O (15%), K7Na[Nab4Ta2O19] • 13H2O (17%), K7Na[Nb3Ta3O19] • 12H2O (16%),
K7Na[Nb2Ta4O19] • 11H2O (13%), K7Na[Ta6O19] • 12H2O (13%).
It should be noted that an assumption that the countercations for each sample is ‘K7Na’
due to the synthesis carried out being identical, being reported by Nyman and co-
workers, (11) as well as being shown in the single crystal measurements.
a
b
c
2θ / deg
Intensity(a.u.)

31
4.3 Perovskite Materials
All perovskite samples were synthesized by hydrothermal synthesis. Either the Nb-
and/or Ta-containing POMs or NbCl5 and/or TaCl5 were placed in an autoclave at
240°C for either 1, 2, or 5 days, along with either KOH or NaOH solution. The resulting
white powder was washed with generous amounts of H2O, collected and air dried at
room temperature for collection. PXRD was initially done to determine the purity of the
samples, however HRPXRD was subsequently done to determine space groups and
crystal structures. Figures 14 and 15 show the HRPXRD patterns of various
perovskites synthesized using both chlorides and POMs as starting materials. Figure
14 illustrates the potassium perovskites while Figure 15 the sodium perovskites. The
overall outline of possible perovskite synthesis done in this thesis can be seen in
Appendix H.
The space groups and lattice structures of the potassium and sodium niobates and
tantalates have been widely studied and published for materials prepared by solid state
synthesis. The following table shows the established structures and corresponding
lattice parameters of K- and Na- perovskites:

32
Table 3: Table of established niobate and tantalate perovskite space groups and
lattice parameters
Perovskite Crystal
System
Space
Group
a/ Å b/ Å c/ Å V/ Å
3
Reference
KNbO3 Orthorhombic Amm2 3.975 5.692 5.719 129.266 (28)
KTaO3 Cubic Pm̅m 3.988
(2)
3.988
(2)
3.988(2
)
63.44 (29)
NaNbO3 Orthorhombic Pbcm
or
P21ma
5.504(1)
5.571(1)
5.570
(1)
7.766
(1)
15.517
(1)
5.513
(1)
475.709
238.517
(30)
NaTaO3 Orthorhombic Pbnm 5.476(1) 5.521
(1)
7.789
(2)
235.528 (31)
In order to determine and compare the space group and lattice parameters, the
samples were first compared to the established data. Refer to Appendix I for direct
single comparisons between products synthesized from only chlorides as well as only
POMs.

33
As seen in Table 3, the perovskites formed are mostly orthorhombic, with only KTaO3
being cubic as expected. KTaO3 and KNb0.5Ta0.5O3 from the chloride require further
investigation as it appears that the former can be fitted by two cubic perovskites while
the latter appears phase impure.
Figure 14: HRPXRD of Potassium Perovskites
(a) KNbO3_chloride, (b) KNbO3_POM (c) KNb0.5Ta0.5O3_chloride, (d)
KNb0.5Ta0.5O3_POM, (e) KNb0.33Ta0.67O3_POM (f) KTaO3_chloride, (g)
KTaO3_POM; zoomed plot represents peaks at 55.5 to 56.8°.
2θ / deg
Intensity(a.u)
a
b
c
d
f
g
e

34
Table 4: Space groups and refined lattice parameters of K-perovskites
Sample Space
Group
3
Rwp /%
KNbO3 –
chloride
Amm2 3.976(7) 5.694
(13)
5.717
(12)
129.481(5) 20.665
KTaO3 – POM Pm̅m 3.990(1) - - 63.522(4) 10.297
KTa0.67Nb0.33O3
– POM
Amm2 3.994(5) 5.6678(9) 5.653
(10)
128.011(2) 13.191
KTa0.50Nb0.50O3
– POM
Amm2 4.027(8) 5.6574(18) 5.661
(20)
128.991(7) 13.547
KNbO3 – POM Amm2 4.036(17) 5.654(48) 5.677
(46)
129.563(10) 18.839
Figure 15: HRPXRD of Sodium Perovskites (a) NaNbO3_chloride, (b)
NaNbO3_POM (c) NaNb0.5Ta0.5O3_chloride, (d) NaNb0.5Ta0.5O3_POM, (e)
NaNb0.33Ta0.67O3_POM (f) NaTaO3_chloride, (g) NaTaO3_POM; zoomed plots
represent peaks from 57.0 to 59.0°.
2θ / deg
b
c
g
d
e
f
Intensity(a.u)
a

35
The Na- perovskites formed are all orthorhombic, (Table 5), with NaNbO3 from both the
chlorides and POM are distinctly Pbcm rather than Pbnm, as expected. With the
sample NaNb0.5Ta0.5O3 from the chloride, the space group is most likely one of the two
rather than any other possible space group, however neither perfectly fit. Further
analysis is required on these samples.
Table 5: Space groups and lattice parameters of Na-perovskites
Sample Space
Group
3
Rwp /%
NaTaO3 –
chloride
Pbnm 5.482(4) 5.524(5) 7.795(6) 236.120(3) 11.444
NaTa0.5Nb0.5O3
– chloride
Pbnm 5.511(21) 5.558(26) 7.789(19) 238.671(6) 16.603
Pbcm 5.510(26) 5.557(24) 15.572(43) 476.896
(13)
14.955
NaNbO3 –
chloride
Pbcm 5.511(8) 5.571(5) 15.545(19) 477.360(9) 11.461
NaTaO3 – POM Pbnm 5.488(10) 5.528(12) 7.797(15) 236.589(8) 10.053
NaTa0.67Nb0.33O
3 – POM
Pbnm 5.492(4) 5.533(5) 7.807(6) 237.301(3) 16.196
NaTa0.5Nb0.5O3
– POM
Pbnm 5.496(7) 5.534(9) 7.808(10) 237.514(6) 10.604
NaNbO3 – POM Pbcm 5.508(9) 5.566(6) 15.546(19) 476.690(6) 16.183
Preliminary investigation of sodium containing samples suggest that both the chloride
and POM routes produce crystals with the expected space groups while the potassium
samples appear to not be phase pure when using the POMs, and KNbO3 synthesized
from [Nb6O19]8-
being less crystalline than its chloride counterpart.

36
Solid-state 93
Nb NMR has been preliminarily conducted, which suggests an agreement
with the HRPXRD data. Both samples of NaNbO3 are comparatively similar in the local
Nb environment. The perovskites containing mixed Nb and Ta show a Nb signal
located at approximately -1100 ppm with increasing peak intensities. KNb0.33Ta0.67O3
from the POM has a large peak at around -1050 ppm, KNb0.5Ta0.5O3 from the POM is
approximately half as intense while KNb0.5Ta0.5O3 using chlorides has a slightly less
intense peak. KNbO3 from the chlorides and POMs are unexpectedly different. The
peak for the POM synthesised perovskite is located at around -1050 ppm with a slightly
narrower peak compared to that synthesized using the chlorides which is located at
around -1075 ppm with a very broad peak. A more in-depth analysis is currently being
conducted on all synthesized samples at the University of St Andrews. Appendix J
shows the 93
Nb solid-state NMR spectra.
4.4 Filling of Carbon Nanotubes
The attempted filling of carbon nanotubes was done using solution filling. Initially
{K7Na[Nb4Ta2O19]} and Emmanuel Flahaut’s double-walled nanotubes were used. In
order to allow for maximum dissolution and dispersion, {K7Na[Nb4Ta2O19]} was
dispersed in 5 mL H2O or EtOH by stirring while the DWNTs were dispersed in 5 mL
EtOH using a sonic probe. Two individual solutions were mixed and allowed to stir. The
mixture was drop-casted onto lacey and holey Cu, carbon coated grids for analysis.
Emmanuel’s DWNTs have an inner diameter of 0.65 – 2 nm which is within the
expected range for DWNTs. When imaged, only the nanotubes were seen with clusters
of the POM located on the outside of the nanotubes, (Figure 16).

37
Figure 16: HRTEM of {K7Na[Nb4Ta2O19]} clusters surrounding a multi-walled carbon
nanotube
It was also observed that the tips of the nanotubes, as well as inside, were covered in
obstructive material, which would prevent the insertion of the POM. To correct this, the
nanotube sample was pre-treated in H2O2. (32) It was reported that the use of H2O2
mildly oxidizes the nanotubes, unlike another known method which uses an acid for
strong oxidation. This prevents large loss of product seen with the harsher conditions of
the acid, and can be done at room temperature. However, when this was observed, no
difference could be seen.
It was then decided that in order for further maximizing of dissolution and dispersion,
alkylammonium salts may be beneficial, as had been used in the previous insertion of
[W6O19] into DWNT. (19) (21) (22) With this in mind, the TMA salt of [Ta6O19]8-
was
synthesized, using the procedures for the synthesis of POMs in this project. Since the
structure is not known, a comparison of the TMA salt of [Ta6O19]8-
and the reported
K8[Ta6O19] was made, (Figure 17).

38
Figure 17: PXRD comparison of (a) TMA salt of [Ta6O19]8-
and (b) K8[Ta6O19]
It can be seen that the POM synthesized is indeed a POM and is mostly likely that of
[Ta6O19]8-
due to the similarity in peak positions to the reported K8[Ta6O19].
When attempting to insert this POM into Emmanuel Flahaut’s DWNTs, it was observed
that the anions were corroding and degrading the carbon walls of the nanotube, (Figure
18). This could be an electron-beam-induced reaction between the Ta of the POM and
carbon of the nanotube walls. The lack of insertion, however, could be due to the high
charge of the [Ta6O19]8-
anion compared to the previously reported [W6O19]2-
anion.
Intensity(a.u.)
2θ / deg

39
Figure 18: Sequence of images showing the TMA salt of [Ta6O19]8-
degrading walls of
E. Flahaut’s DWNTs
The project then turned towards previously reported results, which did show the
successful insertion of the TBA salt of [W6O19]2-
. (19) (21) (22) The TBA salt of
[Nb2W4O19]4-
was thus synthesized to lower the charge of the ion, but keeping the idea
of mixtures of metals. This was done in a multi-step solution synthesis, following the
procedure of Dabbabi and Boyer. (25) A hot solution of [Nb6O19]8-
was added to a
solution of Na2WO4 • 2 H2O and H2O2. Concentrated acetic acid was added to adjust
the pH to 5.5 and resulting solution was refluxed for 2 hours at 80°C. NaHSO3 was
added and then allowed to cool, in which TBAOH was added, solution filtered, and
EtOH added to precipitate the product. The product was filtered, collected, and air dried
at room temperature. When the PXRD patterns were compared between the previously
1
4
2
3

40
synthesized TMA salt of [Ta6O19]8-
, the patterns show similarities, which would suggest
the formation of a POM, (Figure 19). Recrystallization methods are needed to obtain a
defined composition.
Figure 19: PXRD comparison of synthesized TBA-[Nb2W4O19]4-
and TMA-[Ta6O19]8-
The insertion of [Nb2Ta4O19]8-
was then attempted with DWNTs supplied by Sigma
Aldrich, having an average diameter of 3.5 nm. Once dispersed and drop casted onto a
carbon grid, the sample was then analysed and it was observed that some clusters had
been inserted, but no evidence for the single POM, (Figure 20). It was concluded that
the diameter of the carbon nanotubes was too large to allow for single ions to exist;
therefore single walled nanotubes were then to be investigated.
2θ / deg
Intensity(a.u.)

41
Figure 20: HRTEM of clusters of TBA salt of [Nb2W4O19]4-
inside double- and multi-
walled nanotubes
SWNTs supplied by Sigma Aldrich (synthesized by NanoIntegris) were then used to
decrease the inner diameter to 1.2 – 1.7 nm. Clusters were again seen, however
evidence of possible single ions were observed but were only visible in multi-walled
nanotubes within the SWNT sample, (Figure 21). This would suggest the removal of
tantalum and decrease in nanotube diameter has a substantial effect on the
relationship between the anion and the nanotube.
Figure 21: HRTEM of clusters and possible single ions of TBA salt of [Nb2W4O19]4-
inside single and multi-walled nanotubes

42
The presence of possible single ions and clusters of the POM imply the diameter of the
nanotubes is still slightly too large to accommodate single ions. Single ion-like
structures were only observed in multi-walled nanotubes within the single-walled
nanotube sample which further suggests the incorrect diameter of the nanotubes.
5 Conclusion
Salts of [NbxTa6-xO19]8-
with varying Nb and Ta content have been synthesized and
studied using powder and single-crystal X-ray diffraction. Single-crystal XRD was
performed on [Nb3Ta3O19]8-
which indicated the composition of the crystal studied was
K7Na[Nb4Ta2O19] • 13 H2O , leading to the conclusion that the sample was most likely a
mixture of various [NbxTa6-xO19]8-
ions. This was supported when the simulated powder
pattern of the bulk sample for which the crystal was taken did not match the observed
pattern for [Nb4Ta2O19]8-
.
Potassium and sodium perovskite samples were hydrothermally synthesized using the
POM samples as well as using NbCl5 and TaCl5 to study the effect on perovskite
structure and purity. It was observed by using HRPXRD that it is possible to control the
perovskite but resulting in less crystalline materials with a longer reaction time when
POMs were used. Solid-state NMR is in progress which will aid in determining the
composition of the samples, but preliminary data suggest the composition using
various methods differ.
Double-walled nanotubes were first used to be filled by (K,Na)8[NbxTa6-xO19] using a
solution insertion method, however the ions were only visible as clusters outside of the
tubes. In order to increase dissolution of the POM in EtOH as well as observe if any
change would occur due to the ion being an organic salt, TMA-[Ta6O19]8-
was used and
the carbon walls disintegrated in the electron beam, however, the high charge of the
POM could also be preventing its insertion. TBA-[Nb2W4O19]4-
was then used, which
resulted in the observation of clusters inside the double-walled nanotubes. Single-

43
walled nanotubes were then used to decrease the inner diameter of the nanotubes to
prevent clusters from forming allowing single ions to be seen. Smaller clusters and
possible single ions were observed after this alteration however the presence of the
clusters implied the diameter of the tubes was still too large. These first observations
are a significant new result and suggest that with future work, imagining of mixed-metal
POMs within nanotubes should prove possible.
6 Future Work
Future recrystallization and single-crystal investigation should be done to determine
correctly the composition of each POM sample, the corresponding HRPXRD patterns,
and mass spectroscopy should also be measured to determine their compositions,
metal distribution, and structural information. Once this has been clarified, the synthetic
process for the POMs should be considered in order to attempt to further control the
exact composition of each POM to which would then aid in controlling the product when
converting them to perovskites. Additionally, solid-state NMR studies should be
performed for both POM and perovskite samples in order to determine their
compositions and structural trends with varying niobium and tantalum content.
HRPXRD data will be analysed in greater detail to conclude whether the perovskites
synthesized from the POMs have similar or different characteristics regarding structure,
orientation, and crystallinity. TEM should be done on both POM and perovskite
samples to observe the crystal formation. Energy-dispersive X-ray analysis (EDAX)
would be useful to analyse the composition of both the POMs and perovskites, and to
determine the distribution of elements in the materials.
Finally, smaller diameters of carbon nanotubes, as well as nanotubes supplied by
various sources, must be investigated to insert niobium-tungsten-containing POMs into
nanotubes. SWNTs supplied by SWeNT, with a nanotube diameter of 0.7 – 1.1 nm, will
first be used. Various methods of treatment of the nanotubes to increase the number of
single and open nanotubes may be needed, as well as recrystallizing [Nb2W4O19]4-
to

44
obtain a pure sample. This may then lead to the observation of a chain of anions within
a nanotube allowing for behavioural properties and location of each atom within the
structures to be observed.

45
Appendix
Appendix A: Tables of Conducted Experiments
Reactant Amount Product
NbCl5 6.6g K3Nb(O2)4
30% H2O2 75mL
4M KOH 65mL
MeOH 250mL
TaCl5 6.6g K3Ta(O2)4
30% H2O2 75mL
4M KOH 65mL
MeOH 250mL
NbCl5 0.88g K3Nb0.67Ta0.33(O2)4
TaCl5 0.58g
30% H2O2 15mL
4M KOH 13mL
MeOH 550mL
NbCl5 0.66g K3Nb0.5Ta0.5(O2)4
TaCl5 0.875g
30% H2O2 15mL
4M KOH 13mL
MeOH 550mL
NbCl5 0.44g K3Nb0.33Ta0.67(O2)4
TaCl5 1.17g
30% H2O2 15mL
4M KOH 13mL
MeOH 550mL
Reactant Mass Catalyst Amount Solution Amount Product
K3Nb(O2)4 3.18 g Na3VO4 0.11 g H2O 15 mL K7Na[Nb6O19]
KOH 3.82 g
K3Ta(O2)4 4 g Na3VO4 0.11 g H2O 15 mL K7Na[Ta6O19]
KOH 3.82 g
K3Nb(O2)4 3.18 g K3VO4 0.137 g H2O 15 mL K8[Nb6O19]
KOH 3.82 g
K3Nb(O2)4 2.12 g Na3VO4 0.11 g H2O 15 mL K7Na[Nb4Ta2O19]
K3Ta(O2)4 1.34 g
KOH 3.82 g
K3Ta(O2)4 2 g
KOH 3.82 g
K3Nb(O2)4 1.59 g K3VO4 0.137 g H2O 15 mL K8[Nb3Ta3O19]
K3Ta(O2)4 2 g
KOH 3.82 g

46
Reactant Amount Catalyst Amount Solution Amount Product
K3Ta(O2)4 2.67 g
KOH 3.82 g
K3Ta(O2)4 2 g Na3VO4 0.055 g H2O 15 mL TMA-[Ta6O19]8-
TMAOH 6.16 g
K3Nb(O2)4 3.18 g Na3VO4 0.11 g H2O 15 mL TMA-[Nb6O19]8-
TMAOH 12.32 g
K3Nb(O2)4 3.18 g Na3VO4 0.11 g H2O 15 mL TEA-[Nb6O19]8-
TEAOH 4.89 mL
K3Nb(O2)4 3.18 g Na3VO4 0.11 g H2O 20 mL TPA-[Nb6O19]8-
TPAOH 3.05 mL
K3Nb(O2)4 3.18 g Na3VO4 0.11 g H2O 30 mL TBA-[Nb6O19]8-
TBAOH 27.19 g
0.04M
[Nb6O19]8-
10 mL ----------- ----------
Conc.
Acetic
acid 0.5 mL
TBA-
Nb2W4O19]4-
0.5M
Na2W4•
2H2O 10 mL NaHSO3 1 mL
TBAOH 1.5 g EtOH 100 mL
Reactant Amount Solution Amount Time Temp Product
K7Na[Nb3Ta3O19] 500 mg KOH 12 mL
24
hours
200°C KNb0.5Ta0.5O3
K7Na[Nb3Ta3O19] 500 mg KOH 12 mL
24
hours
240°C KNb0.5Ta0.5O3
K7Na[Nb3Ta3O19] 500 mg KOH 12 mL 3 days 240°C KNb0.5Ta0.5O3
K7Na[Nb3Ta3O19] 500 mg NaOH 12 mL 5 days 240°C NaNb0.5Ta0.5O3
K8[Nb3Ta3O19] 500 mg KOH 12 mL 5 days 240°C KNb0.5Ta0.5O3
K8[Nb3Ta3O19] 500 mg NaOH 12 mL 5 days 240°C NaNb0.5Ta0.5O3
K7Na[Nb6O19] 500 mg KOH 12 mL 5 days 240°C KNbO3
K7Na[Nb6O19] 500 mg NaOH 12 mL 5 days 240°C NaNbO3
K7Na[Ta6O19] 500 mg KOH 12 mL 5 days 240°C KTaO3
K7Na[Ta6O19] 500 mg NaOH 12 mL 5 days 240°C NaTaO3
K8[Nb6O19] 500 mg KOH 12 mL 5 days 240°C KNbO3
K8[Nb6O19] 500 mg NaOH 12 mL 5 days 240°C NaNbO3
K7Na[Nb2Ta4O19] 500 mg NaOH 12 mL 5 days 240°C NaNb0.33Ta0.67O3

47
Reactant Amount Solution Amount Time Temp Product
NbCl5 500mg KOH 12 mL
24
hours
240°C KNbO3
NbCl5 500mg NaOH 12 mL
24
hours
240°C NaNbO3
TaCl5 500mg KOH 12 mL
24
hours
240°C KTaO3
TaCl5 500mg NaOH 12 mL
24
hours
240°C NaTaO3
TaCl5 500mg KOH 12 mL
48
hours
240°C KTaO3
TaCl5 500mg NaOH 12 mL
48
hours
240°C NaTaO3
NbCl5 362 mg KOH 12 mL
24
hours
240°C KNb0.67Ta0.33O3
TaCl5 240 mg
NbCl5 362 mg NaOH 12 mL
48
hours
240°C NaNb0.67Ta0.33O3
TaCl5 240 mg
24
hours
240°C KNb0.5Ta0.5O3
TaCl5 132 mg
48
hours
240°C NaNb0.5Ta0.5O3
TaCl5 132 mg
24
hours
240°C KNb0.33Ta0.67O3
TaCl5 480 mg
48
hours
240°C NaNb0.33Ta0.67O3
TaCl5 480 mg

48
Successful
Unsuccessful
Pending
POM Solvent SWNT/DWNT Source Solvent
K7Na[Nb3Ta3O19] solution DWNT E. Flahaut H2O
K7Na[Nb3Ta3O19] H2O DWNT Sigma EtOH
K7Na[Nb3Ta3O19] EtOH DWNT Sigma EtOH
K7Na[Nb3Ta3O19] EtOH DWNT (H2O2 treated) Sigma EtOH
TMA-[Ta6O19]8-
EtOH DWNT (H2O2 treated) Sigma EtOH
TBA-[Nb2W4O19]4-
EtOH DWNT (H2O2 treated) Sigma EtOH
TBA-[Nb2W4O19]4-
EtOH SWNT NI EtOH
TBA-[Nb2W4O19]4-
EtOH SWNT (heat treated) NI EtOH
TBA-[Nb2W4O19]4-
EtOH SWNT SWeNT EtOH

49
Appendix B: IR Spectra of K3Nb(O2)4 and K3Ta(O2)4; full and closeup
Intensity(a.u.)
Intensity(a.u.)
Wavenumber (cm-1
)
Wavenumber (cm-1
)

50
Appendix C: TGA Measurement and comparison between K3Nb(O2)4
and K3Ta(O2)4

51
Appendix D: PXRD comparison of observed (a) K8[Nb6O19] and (b)
K8[Nb3Ta3O19]Intensity(a.u)
2θ / deg
a
b

52
Appendix E: Bond lengths in [Nb6O19]8-
, [Ta6O19]8-
, and
K7Na[Nb4Ta2O19] • 13 H2O_single crystal
[Nb6O19]8-
[Ta6O19]8-
K7Na[Nb4Ta2O19]_single crystal
Nb1 O3 1.7903 Ta1 O8 1.8392
Nb1|
Ta1
O1
0 1.799
Nb4|
Ta4 O6 1.7879
O6 1.9786 O4 1.9284
O1
4 1.986 O16 1.9932
O7 1.9893 O7 1.9542
O1
3 1.989 O12 1.9937
O10 1.9935 O5 1.9904
O1
2 1.992 O7 1.994
O9 1.999 O6 2.006
O1
1 1.996 O5 1.9985
O1 2.3782 O1 2.3776 O1 2.388 O1 2.3595
Nb2 O2 1.7947 Ta2 O9 1.7146
Nb2|
Ta2 O4 1.795
Nb5|
Ta5 O2 1.8164
O8 1.9749 O2 1.9391
O1
7 1.981 O3 1.9673
O4 1.9795 O3 1.9727 O3 1.988 O18 1.9887
O7 1.997 O6 1.9963
O1
3 1.992 O14 1.9938
O10 1.997 O4 2.0327 O5 2.005 O9 1.9942
O1 2.3434 O1 2.3457 O1 2.382 O1 2.3603
Nb3 O5 1.796 Ta3 O10 1.8
Nb3|
Ta3 O8 1.792
Nb6|
Ta6 O19 1.8314
O8 1.9794 O2 2.0288 O9 1.984 O17 1.9476
O9 1.9831 O3 2.0343
O1
5 1.993 O18 1.9729
O4 1.9881 O7 2.0494 O7 2.001 O16 1.9903
O6 1.9984 O5 2.0616
O1
1 2.009 O15 2.0194
O1 2.3721 O1 2.3735 O1 2.357 O1 2.3169
Yellow: [Nb6O19]8-
Orange: [Ta6O19]8-
Blue: K7Na[Nb4Ta2O19] • 13 H2O
Green values are terminal oxygens bound to each addendum atom.
*All values are in Ångström.

53
Appendix F: TGA comparison between K7Na[Nb6O19] and
K7Na[Ta6O19]

54
Appendix G: TGA comparison between mixed-metal POMs

55
Appendix H: Outline of routes considered for perovskite synthesis
K7Na[Nb4Ta2O19]
KNb0.67Ta0.33O3
K7Na[Nb2Ta4O19]
KNb0.33Ta0.67O3
NbCl5 KNbO3 NbCl5
NaNbO3
NbCl5+TaCl5 2:1
KNb0.67Ta0.33O3
NbCl5+TaCl5 2:1
NaNb0.67Ta0.33
O3
K8[Nb6O19] NaNbO3K8[Nb6O19] KNbO3
K7Na[Nb3Ta3O19]
KNb0.5Ta0.5O3
K7Na[Nb4Ta2O19]
NaNb0.67Ta0.33O3
K7Na[Nb3Ta3O19]
NaNb0.5Ta0.5O3
K7Na[Nb2Ta4O19]
NaNb0.33Ta0.67
O3
K7Na[Ta6O19]
KTaO3
K7Na[Ta6O19]
NaTaO3
NbCl5+TaCl5 1:1
KNb0.5Ta0.5O3
NbCl5+TaCl5 1:1
NaNb0.5Ta0.5O3
NbCl5+TaCl5 1:2
KNb0.33Ta0.67O3
TaCl5 KTaO3
NbCl5+TaCl5 1:2
NaNb0.33Ta0.67
O3
TaCl5 NaTaO3

56
Appendix I: Comparison of samples made from chlorides and made
from POMs
K-salts from Chlorides:
(a) KTaO3, (b) KNb0.5Ta0.5O3, (c) KNbO3
Intensity(a.u.)
2θ / deg
a
b
c

57
K-salt from POMs:
(a) KNbO3, (b) KNb0.5Ta0.5O3, (c) KNb0.5Ta0.5O3, (d) KTaO3
a
b
c
d
Intensity(a.u.)
2θ / deg

58
Na-salt from Chlorides
(a)NaTaO3, (b) NaNb0.5Ta0.5O3, (c) NaNbO3
a
b
c
Intensity(a.u.)
2θ / deg

59
Na-salt from POMs:
(a) NaNbO3, (b) NaNb0.5Ta0.5O3, (c) NaNb0.5Ta0.5O3, (d) NaTaO3
Intensity(a.u.)
a
b
c
d
2θ / deg

60
Appendix J: 93
Nb solid-state NMR of perovskite samples
AC7= NaNbO3 from POM
AC6= NaNbO3 from chloride
AC5= KNb0.5Ta0.5O3 from chloride
AC4= KNb0.5Ta0.5O3 from POM
AC3= KNb0.33Ta0.67O3 from POM
AC2= KNbO3 from POM
AC1= KNbO3 from chloride

61
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