1. Physics and Chemistry of ABO3
Nanostructures from First Principles
Ghanshyam Pilania
Chemical, Materials & Biomolecular Engineering
Institute of Materials Science
University of Connecticut
Principal Advisor: Prof. R. Ramprasad
Associate Advisor: Prof. P. Gao
Associate Advisor: Prof. G. Rossetti, Jr.
Ph.D. Dissertation Proposal
3. Novel polarization states in ABO3 nanowires
(p,T) surface phase diagrams of ABO3 surfaces
“Vortex” v/s “axial” polarization states
Effect of size, surface termination and axial strain on the
polarization states
Outline
Methodology to construct surface phase diagrams
Calculated (p,T) surface phase diagrams for LaMnO3 and
PbTiO3 (001) surfaces
Remaining work
Impact of work
5. Ferroelectricity in bulk perovskites
Ferroelectricity: a collective phenomena
A balance between
long range Coulombic force (favor ferroelectric state)
short range repulsive forces (resist ferroelectric state)
Dipole moment per unit volume = Polarization
T
Tc
Ferroelectric
Paraelectric
ABO3 perovskite
Energy
P
Paraelectric state
ABO3 perovskite Ferroelectric Well
Energy
P
Paraelectric state
Energy
P
Ferroelectric state
Energy
P
7. Ferroelectricity in Nanostructures
P
Depolarizing
Field
P
No depolarizing
Field
No depolarizing
Field
Closure domain
Prosendeev & Bellaiche (PRB 2007)
PFM results indicate possible presence of non-
rectilinear polarization in PZT nanodots
Rodriguez et al (Nanoletters, 2009)
8. ABO3 Nanowires – Our DFT Study
2x2-AO-terminated
nanowire
2x2-BO2-terminated
nanowire
AO-plane
BO2-plane
AO-plane
BO2-plane
Construction of ABO3 nanowires
10. Spanier et al, Nano Lett. 6, 735 (2006)
0.8 nm
Off-axis Polarization in BaTiO3 nanowires
BaTiO3 Nanowires – Experimental Study
11. PbTiO3 Nanowires – Our DFT Study
c (Å)
Fa
Fa
Fa
Fa
P
1x1 to 4x4-PbO
Fv
Shimada et al, PRB 79, 024102 (2009)
c tetragonal Bulk
acubic Bulk
P
P
P
4x4-TiO2
τ=rxP
Unit cell decomposed
dipole moments
12. PbTiO3 Nanowires vs. Terminations
Strain-induced phase transition: vortex axial polarization
4x4-TiO2-terminated
nanowire
[001]
Axial compressive Strain
Axial Tensile Strain
4x4-PbO-terminated
nanowire
Four possible switchable polarization states
Vortex (clockwise/counter-clockwise), Axial (positive/negative)
13. PbTiO3 nanowires display switchable rectilinear (axial)
and non-rectilinear (vortex) polarization configurations
Control of polarization states
axial Strain and surface terminations
16. R. J. H. Voorhoeve, D. W. Johnson, Jr., J. P. Remeika, P. K. Gallagher
SO4
-2
Dead site Active site
Sulfur poisoning
26 MARCH 2010 VOL 327 SCIENCE
Chang Hwan Kim, Gongshin Qi, Kevin Dahlberg, Wei Li
Perovskite Surfaces in Catalysis
20. (1x1) AO-terminated (1x1) BO2-terminated
Formation Energies
Cubic LaMnO3 and PbTiO3 surface phase diagrams
A
21. Relaxed geometries for most favored adsorption sites
Cubic LaMnO3 and PbTiO3 surface phase diagrams
22. Perovskite surfaces in contact with O2 (g)
0
0
0 2
2
2
2
ln
)
,
(
)
,
0
(
)
,
(
p
p
T
k
p
T
p
K
T
p
T
O
B
O
O
O
Assuming ideal gas behavior for O2
2
2
1
O
O
Surface-O*↔ Surface + ½ O2 (g)
23. Surface phase diagrams for surfaces in contact with O2
PbTiO3 (001) TiO2-terminated
log
P
O2
100% O ad-atom coverage
Partial O vacancy
coverage
Partial coverage of O ad-atom
Clean surface
100% O vacancy
T (K)
LaMnO3 (001) MnO2-terminated
100% O vacancy
Partial coverage of
O ad-atom
100% O ad-atom coverage
log
P
O2
T (K)
24. Remaining Work
Electric field response of the vortex polarization state in PbTiO3
nanowires
Efield ?
Dielectric tensor of ferroelectric nanowires
4x4-PbO terminated nanowire (axial polarization)
4x4-TiO2 terminated nanowire (vortex polarization)
Effect of surface passivation (by various species such as –OH,
H, -CH3 etc.) on polarization states in PbTiO3 nanowires
25. Thermodynamics of environment dependent interaction of various
gases on the (001) surface of ABO3 type perovskites
NO, NO2, N2, O2
(gases)
Adsorption site
Equilibrium geometry
Electronic structure
Energetics
Kinetics ??
Remaining Work
26. Impact of Work
0 1 0 0
Non volatile Ferroelectric memory
Potential to increase present memory storage density by five order of magnitude
How to shrink the
hard drive?!!
27. Impact of Work
DeNOx processes
NO + CO +
unburned
hydrocarbons
catalytic
converter
CO CO2
NOx
N2 + O2
CnHm CO2+H2O
LaCoO3 (○)
La0.9Sr0.1CoO3 (●)
LaMnO3 (□)
La0.9Sr0.1MnO3 (■)
commercial DOC (▲)
28. List of Publications
G. Pilania, S. P. Alpay and R. Ramprasad, "Ab initio study of ferroelectricity in
BaTiO3 nanowires", Phys. Rev. B 80, 014113(1)-014113(7)- (2009).
G. Pilania, D. Q. Tan, Y. Cao, V. S. Venkataramani, Q. Chen and R. Ramprasad,
"Ab initio study of antiferroelectric PbZrO3 (001) surfaces", J. Mater. Sci. 44, 5249-
5255 (2009).
G. Pilania, T. Sadowski and R. Ramprasad, "Oxygen adsorption on CdSe
Surfaces: A case study of asymmetric anisotropic growth through Ab initio
computations", J. Phys. Chem. C. 113(5), 1863-1871 (2009).
J. D. Doll, G. Pilania, R. Ramprasad and F. Papadimitrakopoulos, "Oxygen-
Assisted Unidirectional Growth of CdSe Nanorods Using a Low-Temperature
Redox Process", Nano Lett., 10 (2), 680-685 (2010).
G. Pilania and R. Ramprasad “Vortex -Polarization Instability in PbTiO3
nanowires”, under review.
G. Pilania and R. Ramprasad “Thermodynamics of environment dependent
oxygen adsorption and vacancy formation on cubic PbTiO3 and LaMnO3 (001)
surfaces”, In preparation.
29. Acknowledgments
Group Members :
Ning, Tang, Tom, Hong, Satyesh, Chenchen, Yenny
Committee members:
Profs. Rampi Ramprasad, Puxian Gao and George A. Rossetti, Jr.
Profs. Rainer Hebert and Pamir S. Alpay
Computational resources:
IMS computation clusters; SGI supercomputer in SoE and Teragrid
Funding:
NSF & ONR
