EXAFS for Structural Characterization, Extended X-ray Absorption Fine Structure

Clean Energy Technology Laboratory, Department of Applied Chemical Engineering
EXAFS for Structural Characterization

Why Extended X-ray Absorption Fine Structure ?
Diffraction XAFS
Diffraction XAFS
• Range of probe • Probes average, long
range structure ( > 10 nm)
• Probes local structural
environment ( < 1nm)
• Probes crystalline phase
only
• Probes local environment of
element irrespective of
crystallite particle size, of
crystalline/amorphous solids,
solutions, gases, etc.

XAS (X-ray Absorption Spectroscopy)
This is a general purpose term used to describe any experiment involving absorbed photons. It includes all of the acronyms below.
XANES (X-ray Absorption Near Edge Structure)
This is the portion of the X-ray absorption spectrum that extends from below the Fermi energy to about 20 volts above the Fermi
energy. It is purported to contain a wealth of structural and electronic information about the measured material.
NEXAFS (Near-Edge X-ray Absorption Fine Structure)
This is a synonym for XANES. There is no difference between the two. XANES should be used instead of NEXAFS.
EXAFS (Extended X-ray Absorption Fine Structure)
This is the portion of the absorption spectrum which starts about 20 volts above the Fermi energy. Typically the EXAFS is analyzed
by removing a background function with AUTOBK or a similar program. The resulting oscillatory function is the Fourier transformed.
XAFS (X-ray Absorption Fine Structure)
This is sometimes used a synonym for EXAFS, but is more appropriately used to mean the entire absorption spectrum. That is,
XAFS = XANES+EXAFS, thus XAFS is more a synonym for XAS than for EXAFS.
SEXAFS (Surface Extended X-ray Absorption Fine Structure)
This is EXAFS performed at a glancing angle so that only the region near the surface of the sample if probed.
DAFS (Diffraction Anomalous Fine Structure)
This is a resonant diffraction technique which combines the short range sensitivity of XAFS with the crystallographic sensitivity of
diffraction. This acronym was chosen to emphasize the similarity in theory and analysis of this technique with XAFS.
XAFS Acronyms

Synchrotron radiation (SR) is ideal source for EXAFS
Intense, directional and spectrally monotonous

Beamline status of PAL
From
http://pal.postech.ac.kr/

9B High Resolution Powder Diffraction

7D and 8C : XAFS and nano XAFS

Why laboratory EXAFS spectrometer ?
[1] Ease of experiments
[2] Unlimited use of instrument
[3] Special samples, in-situ etc.
[1] Synchrotronlike resolution, 3 eV of much low
intensity, 106 cps vs. 109 cps from SR
[2] S/N ~ 1000: EXAFS oscillation is less than 10% of
background (accuracy better than 0.1%)

Main problems in EXAFS measurement
[1] low intensity of X-ray flux
[2] degradation of the spectrum by 2nd and 3rd harmonics
[3] effect of non-smooth spectra distribution
[1] an extremely high tube current, e.g. 1,000 mA
(100 mA)
[2] narrow line focus, e.g. 0.1 mm at 6 deg take off
[3] low tube voltage operation, 10 ~ 30 kV (~ 40 kV)
[4] LaB6 or other-tungsten filament

Typical arrangement in Lab-EXAFS measurement

Rowland circle: Johann crystal
nλ=2dsinθ, θ1 =θ2= θ3= θ4= θ

Principle of a linear spectrometer

Type of monochromator crystals
[1] Effective utilization of X-rays
[2] Elimination of unnecessary X-rays originating
from different order reflections

R-EXAFS 3000V laboratory EXAFS spectrometer

R-EXAFS 2100S laboratory EXAFS spectrometer

X
Transmitted x-rays
Incident x-rays
Scattered x-rays
Fluorescence x-rays
If Photoelectrons
I
I0
μ X = ln
I0
I
Arrangement in R-XAS (Rigaku)

Photograph of R-XAS (3 kw X-ray generator)

109
Mt
(266)
108
Hs
(265)
107
Bh
(262)
106
Sg
(263)
105
Db
(260)
104
Rf
(257)
89
Ac~
(227)
88
Ra
(226)
87
Fr
(223)
86
Rn
(222)
85
At
(210)
84
Po
(210)
83
Bi
209.0
82
Pb
207.2
81
Tl
204.4
80
Hg
200.5
79
Au
197.0
78
Pt
195.
77
Ir
190.2
76
Os
190.2
75
Re
186.2
74
W
183.9
73
Ta
180.9
72
Hf
178.
57
La*
138.
56
Ba
137.3
55
Cs
132.9
54
Xe
131.3
53
I
126.9
52
Te
127.6
51
Sb
121.8
50
Sn
118.7
49
In
114.8
48
Cd
112.4
47
Ag
107.9
46
Pd
106.
45
Rh
102.9
44
Ru
101.1
43
Tc
(98)
42
Mo
95.94
41
Nb
92.91
40
Zr
91.2
39
Y
88.9
38
Sr
87.62
37
Rb
85.47
36
Kr
83.80
35
Br
79.90
34
Se
78.96
33
As
74.92
32
Ge
72.59
31
Ga
69.72
30
Zn
65.39
29
Cu
63.55
28
Ni
58.6
27
Co
58.47
26
Fe
55.85
25
Mn
54.94
24
Cr
52.00
23
V
50.94
22
Ti
47.8
21
Sc
44.9
20
Ca
40.08
19
K
39.10
------- VIII -------
------- 8 -------
18
Ar
39.95
17
Cl
35.45
16
S
32.07
15
P
30.97
14
Si
28.09
13
Al
26.98
12
IIB
2B
11
IB
1B
10
9
8
7
VIIB
7B
6
VIB
6B
5
VB
5B
4
IVB
4B
3
IIIB
3B
12
Mg
24.31
11
Na
22.99
10
Ne
20.18
9
F
19.00
8
O
16.00
7
N
14.01
6
C
12.01
5
B
10.81
4
Be
9.012
3
Li
6.941
2
He
4.003
2
IIA
2A
1
H
1.008
71
Lu
175.0
70
Yb
173.0
69
Tm
168.9
68
Er
167.3
67
Ho
164.9
66
Dy
162.5
65
Tb
158.9
64
Gd
157.3
63
Eu
152.0
62
Sm
150.4
61
Pm
(147)
60
Nd
144.2
59
Pr
140.9
58
Ce
140.1
109
Mt
(266)
108
Hs
(265)
107
Bh
(262)
106
Sg
(263)
105
Db
(260)
104
Rf
(257)
89
Ac~
(227)
88
Ra
(226)
87
Fr
(223)
86
Rn
(222)
85
At
(210)
84
Po
(210)
83
Bi
209.0
82
Pb
207.2
81
Tl
204.4
80
Hg
200.5
79
Au
197.0
78
Pt
195.
77
Ir
190.2
76
Os
190.2
75
Re
186.2
74
W
183.9
73
Ta
180.9
72
Hf
178.
57
La*
138.
56
Ba
137.3
55
Cs
132.9
54
Xe
131.3
53
I
126.9
52
Te
127.6
51
Sb
121.8
50
Sn
118.7
49
In
114.8
48
Cd
112.4
47
Ag
107.9
46
Pd
106.
45
Rh
102.9
44
Ru
101.1
43
Tc
(98)
42
Mo
95.94
41
Nb
92.91
40
Zr
91.2
39
Y
88.9
38
Sr
87.62
37
Rb
85.47
36
Kr
83.80
35
Br
79.90
34
Se
78.96
33
As
74.92
32
Ge
72.59
31
Ga
69.72
30
Zn
65.39
29
Cu
63.55
28
Ni
58.6
27
Co
58.47
26
Fe
55.85
25
Mn
54.94
24
Cr
52.00
23
V
50.94
22
Ti
47.8
21
Sc
44.9
20
Ca
40.08
19
K
39.10
------- VIII -------
------- 8 -------
18
Ar
39.95
17
Cl
35.45
16
S
32.07
15
P
30.97
14
Si
28.09
13
Al
26.98
12
IIB
2B
11
IB
1B
10
9
8
7
VIIB
7B
6
VIB
6B
5
VB
5B
4
IVB
4B
3
IIIB
3B
12
Mg
24.31
11
Na
22.99
10
Ne
20.18
9
F
19.00
8
O
16.00
7
N
14.01
6
C
12.01
5
B
10.81
4
Be
9.012
3
Li
6.941
2
He
4.003
2
IIA
2A
1
H
1.008
71
Lu
175.0
70
Yb
173.0
69
Tm
168.9
68
Er
167.3
67
Ho
164.9
66
Dy
162.5
65
Tb
158.9
64
Gd
157.3
63
Eu
152.0
62
Sm
150.4
61
Pm
(147)
60
Nd
144.2
59
Pr
140.9
58
Ce
140.1
Ge(220) bent crystal, K edge
(4492 – 11866 eV) LIII edge
(4492 – 11866 eV) LIII edge
(14325 – 25514 eV)
(14325 – 25514 eV)
Si(400) (8947 – 16716 ev)
K edge
LIII edge
Crystal and energy range of R-XAS

0 1 2 3 4 5 6
0
10
20
30
40
50
60
LiMnCoNiO2
(Co)-Pohang Accelerator
Fourier
trasform
R (A)
Exp.
Fitting
7400 7600 7800 8000 8200 8400
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
Normalized
Absorbance
(a.u.)
Energy (eV)
LiMnCoNiO2
(Co)-Pohang Accelerator
-6.9
E0/eV
0 (0.0004)
33(0.0004)
σ2 (pm2)c
12.0
Rf(%)d
12.28(0.6529)
11.49(0.7219)
1.916(0.0276)
2.846(0.0025)
Co-O
Co-Co
Co
Nb
R (Å)a
Atomic pair
-6.9
E0/eV
0 (0.0004)
33(0.0004)
σ2 (pm2)c
12.0
Rf(%)d
12.28(0.6529)
11.49(0.7219)
1.916(0.0276)
2.846(0.0025)
Co-O
Co-Co
Co
Nb
R (Å)a
Atomic pair
Structure parameters of LiMnCoNiO2(Co)
7200 7400 7600 7800 8000 8200 8400
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
Energy (eV)
Normalized
Absorbance
(a.u.)
LiMnCoNiO2
(Co)-CDFC
0 1 2 3 4 5
0
10
20
30
40
50
60
R (A)
Exp.
Fitting
LiMnCoNiO2
(Co)-CDFC
-5.47
E0/eV
0
32(0.0006)
σ2 (pm2)c
15
Rf(%)d
12.79(0.7)
10.56(0.7)
1.915(0.0030)
2.844(0.0027)
Co-O
Co-Co
Co
Nb
R (Å)a
Atomic pair
-5.47
E0/eV
0
32(0.0006)
σ2 (pm2)c
15
Rf(%)d
12.79(0.7)
10.56(0.7)
1.915(0.0030)
2.844(0.0027)
Co-O
Co-Co
Co
Nb
R (Å)a
Atomic pair
Data comparison: R-XAS vs. Synchrotron EXAFS

Data comparison: R-XAS vs. Synchrotron EXAFS
0 1 2 3 4 5 6
0
10
20
30
40
50
R (A)
Fourier
trasform
Exp.
Fitting
LiMnCoNiO2
(Mn)-Pohang Accelerator
6200 6400 6600 6800 7000 7200 7400 7600
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2 LiMnCoNiO2
(Mn)-Pohang Accelerator
Normalized
Absorbance
(a.u.)
Energy (eV)
-5.1
E0/eV
0 (0.0005)
18(0.0005)
σ2 (pm2)c
14.0
Rf(%)d
10.23(0.7041
)
6.41(0.6497)
1.9030.0037)
2.877(0.0036)
Mn-O
Mn-Mn
Mn
Nb
R (Å)a
Atomic pair
-5.1
E0/eV
0 (0.0005)
18(0.0005)
σ2 (pm2)c
14.0
Rf(%)d
10.23(0.7041
)
6.41(0.6497)
1.9030.0037)
2.877(0.0036)
Mn-O
Mn-Mn
Mn
Nb
R (Å)a
Atomic pair
Structure parameters of LiMnCoNiO2(Mn)
6300 6400 6500 6600 6700 6800 6900 7000 7100
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Normalized
Absorbance
(a.u.)
Energy (eV)
LiMnCoNiO2
(Mn)-CDFC
0 1 2 3 4 5 6
0
10
20
30
40
50
R (A)
LiMnCoNiO2
(Mn)-CDFC
Exp.
Fitting
-2.95
E0/eV
23(0.0001)
21(0.0002)
σ2 (pm2)c
19.0
Rf(%)d
8.12(0.6)
5.41(0.6)
1.905(0.0044)
2.874(0.0045)
Mn-O
Mn-Mn
Mn
Nb
R (Å)a
Atomic pair
-2.95
E0/eV
23(0.0001)
21(0.0002)
σ2 (pm2)c
19.0
Rf(%)d
8.12(0.6)
5.41(0.6)
1.905(0.0044)
2.874(0.0045)
Mn-O
Mn-Mn
Mn
Nb
R (Å)a
Atomic pair

6520 6540 6560 6580 6600 6620
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Mn K edge
Absorbance
(a.u.)
Energy (eV)
5-1(Mn)
5-2(Mn)
5-3(Mn)
5-4(Mn)
5-5(Mn)
Mn2
O3
MnO2
0 1 2 3 4 5 6
0
10
20
30
Fourier
transform
R (A)
5-1(Mn)
5-2(Mn)
5-3(Mn)
5-4(Mn)
5-5(Mn)
Analysis Result in LiNi1/3 Co1/3 Mn1/3O2 for Cathode Materials

Redox property of LiFePO4 electrodes by in-situ XAS
A. Deb et al. Electrochemica Acta 50 (2005) 5200
Normalized XANES data at the Fe K edge during charge. Radial distribution function obtained after Fourier
transformation of kχ(k) observed at the stages (a) A,
(b) B, (c) C, (d) D and (e) E. The solid line and circle
indicate the theoretical fit and experimental data,
respectively.
Fe2+ → Fe3+
in LiFePO4 in FePO4

Structural parameter change during cell cycling
First shell average metal-oxygen and second shell average metal-
phosphorus bond length changes during Li/LixFePO4 cell cycling

Electronic structure change upon charge-discharge
for LiNi1/3 Co1/3 Mn1/3O2 (H. Kobayashi et al. J. Power Sources 146 (2005) 640)
Ni K-edge XANES spectra for Li1-yNi1/3Mn1/3Co1/3O2 (y=0-0.7)
Ni2+ → Ni3+ → Ni4+

Metal-O bond length as evidence for change of valence state
Co3+ → Co4+

Preparation of Mn-substituted LiFeO2
with advanced battery performance
XRD patterns of (a) 10%, (b) 30%, (c) 50% Mn-substituted LiFeO2 and
LixMnO2. These materials were calcined at 350 °C for 15 h in argon.
Y. S. Lee et al. Electrochemistry Communications 5 (2003) 359

Specific discharge capacity versus cycle number for Li/Mn-substituted
LiFeO2 cells. (a) 10%, (b) 30%, (c) 50% Mn-substituted LiFeO2. The test
conditions were current density of 0.4 mA/cm2 between 1.5-4.5 V at 25 °C.
Cycle property of Mn-substituted LiFeO2

10 20 30 40 50 60 70 80
LiFe0.8
Ni0.2
O2
-Lix
MnO2
(60%)
LiFe0.6
Ni0.4
O2
-Lix
MnO2
(60%)
LiFe0.7
Ni0.3
O2
-Lix
MnO2
(60%)
LiFe0.9
Ni0.1
O2
-Lix
MnO2
(60%)
LiFeO2
-Lix
MnO2
(60%)
Intensity
/
arb.unit
2theta/degree
Preparation of Ni-substituted LiFeO2-LixMnO2

1
2
3
4
5
1
2
3
4
1
2
3
4
0 50 100 150 200
1
2
3
4
1
2
3
4
y=0.0
y=0.1
y=0.3
y=0.4
Cell
voltage
(V)
Capacity(mAh/g)
Cell
voltage
(V)
Cell
voltage
(V)
Cell
voltage
(V)
Cell
voltage
(V)
y=0.2
Charge-discharge capacity of Ni-substituted LiFeO2-LixMnO2

0 10 20 30 40 50
0
50
100
150
200
Capacity(mAh/g)
Cycle Number
LiFeO2
-Lix
MnO2
(60%)
LiFe0.9
Ni0.1
O2
-Lix
MnO2
(60%)
LiFe0.8
Ni0.2
O2
-Lix
MnO2
(60%)
LiFe0.7
Ni0.3
O2
-Lix
MnO2
(60%)
LiFe0.6
Ni0.4
O2
-Lix
MnO2
(60%)
Cycle property of Ni-substituted LiFeO2-LixMnO2

XPS analysis of electrode before and after charge-discharge test
Li1-xFeO2LixMnO2 Li1-xFe0.8Ni0.2O2LixMnO2
Fe: +3 +3
Ni: +2
Mn: +4 +4
Li/Li1-xFeO2LixMnO2 Li/Li1-xFe0.8Ni0.2O2LixMnO2
Fe: +3 +3
Ni: +2 → +2, +3 → +3
Mn: +4 +4
Cycling

Wave vector (nm-1)
0 20 40 60 80 100 120 140 160
k
3
χ(k)
Distance (nm)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
FT
Intensity
XAFS data analysis at Fe K edge
Li1-xFe0.9Ni0.1O2LixMnO2
Li1-xFeO2LixMnO2

Wave vector (nm-1)
0 20 40 60 80 100 120 140
k
3
χ(k)
Distance (nm)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
FT
Intensity
XAFS data analysis at Mn K edge
Li1-xFeO2LixMnO2

XAFS data analysis at Ni K edge
Wave vector (nm-1)
0 20 40 60 80 100 120 140
k
3
χ(k)
Distance (nm)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
FT
Intensity Li1-xFe0.9Ni0.1O2LixMnO2

y, Ni/(Fe+Ni) 0 0.1 0.2 0.3 0.4
RFe-O (nm) 0.197 0.196 0.197 0.194 0.198
RMn-O (nm) 0.190 0.190 0.190 0.190 0.190
RNi-O (nm) 0.204 0.205 0.207 0.204
NFe-O 6.1 6.0 6.2 6.1 6.3
NMn-O 3.4 3.4 3.4 3.0 3.4
NNi-O 4.5 6.7 4.7 5.3
RFe-Fe (nm) 0.299 0.299 0.298 0.297 0.300
RMn-Mn (nm) 0.287 0.288 0.288 0.288 0.288
RNi-(Ni)(nm) 0.292 0.292 0.295 0.293
NFe-Fe 6.1 5.4 4.3 6.6 6.0
NMn-Mn 2.6 2.8 2.8 2.7 2.7
NNi-(Ni) 4.6 9.2 7.8 7.2
Structural parameters of the Li1-xFe1-yNiyO2LixMnO2

In-situ Cell Unit Low-temperature Cell Unit
Special Cell Units for Various Needs
Field of applications can be broadened

장비명 : X-ray Absorption Spectroscopy
모델명 : R-XAS (Rigaku, Japan)
In-situ cell system and Lab-EXAFS

대기중 분석
•온 도 : R.T.
•압 력 : 1bar
•기 체 : Air
•온 도 : R.T. ~ 600 ℃
•진공도 : 10-3 torr
•기 체 : H2, O2, N2, He
in-situ 분석

1단계 : in-situ cell 분해 2단계 : 시료홀더에 시료 삽입
3단계 : 시료홀더 장착 4단계 : 조립
In-situ cell assembly

본체
내부 시스템
In-situ cell controller

In-situ Electrochemical cell

Electrochemical capacitor: RuO2/Carbon-CNT
SEM images of nanocomposite: (a) Electrospun PAN web, (b) Electrospun PAN-CNT web, (c)
Activated PAN web, (d) Activated PAN-CNT web, (e) RuO2/carbon, and (f) RuO2/carbon-CNT.

0 5 10 15 20
100
150
200
250
300
350
400
450
500
550
600
Carbon-CNT
Carbon
Specific
Capacitance
(F/g)
Content of RuO2
(wt%)
0.0 0.2 0.4 0.6 0.8 1.0
-0.025
-0.020
-0.015
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
Current
(A)
Potential (V)
RuO2
/Carbon-CNT
RuO2
/Carbon
Carbon-CNT
Carbon
Preparation of RuO2/Carbon-CNT
1. Impregnation of RuCl3 solution onto the carbon or the carbon-CNT
2. Reduction of ruthenium oxide with NaBH4 solution

Photon Energy (eV)
21800 22000 22200 22400 22600 22800 23000
Absorption
Intensity
Wave Vector (nm-1
)
0 20 40 60 80 100 120 140
k
3
χ(k)
Distance (nm)
0.0 0.1 0.2 0.3 0.4 0.5
FT
Intensity
Data analysis of the XAFS obtained at Ru K edge

Distance (nm)
0.0 0.1 0.2 0.3 0.4 0.5
FT
Intensity
Curve fitting of the XAFS obtained at Ru K edge
Pair N R (nm) σ2 (pm2)
Ru-O 2 1.833 14.5
Ru-O 4 2.014 21.0
Ru-Ru 1 3.095 79.6

R (A)
0 1 2 3 4 5
FT
Intensity
0
1
2
3
4
5
Wave vector (k
-1
)
0 2 4 6 8 10 12 14
k
3
χ(k)
-4
-3
-2
-1
0
1
2
3
4
Extended X-ray absorption fine structure at Pd
K edge of 8 wt% Pd nanoporous carbon
Pd in the carbon framework contained the Pd-Pd and
Pd-C coordination, which indicated the formation of
Pd/PdC nanoparticles.

X-ray absorption energy, E-E0 (eV)
-100 -80 -60 -40 -20 0 20 40 60 80 100
X-ray
absorption
(a.u.)
2 wt% Pd in carbon
4 wt% Pd in carbon
8 wt% Pd in carbon
Edge shift ~ 5 eV
X-ray absorption near edge structure at Pd K
edge as function of Pd concentration

Structural parameters of Pd incorporated
nanoporous carbon from the curve fit
Pd wt% Pair CN R σ2 (pm2)a
4 Pd-Pd 1.6 2.71 48
Pd-C 1.6 2.77 -
8 Pd-Pd 1.6 2.75 66
Pd-C 1.3 2.56 -
aThe Debye-Waller factor. The many reduction factor was assumed
to be 0.9.
Identification of Pd-C bond was direct evidence for the
formation of PdC in the nanoporous carbon framework.

EXAFS for Structural Characterization, Extended X-ray Absorption Fine Structure

More Related Content

Similar to EXAFS for Structural Characterization, Extended X-ray Absorption Fine Structure

More from KikiRezkiLestari1

Recently uploaded

EXAFS for Structural Characterization, Extended X-ray Absorption Fine Structure