Download - Enhanced Thermoelectric properties via oxygen non- stoichiometry and strain of La 2 NiO 4+ δ
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Project MAT 2009-08165
Ramón y Cajal Program
Financial support from:
Víctor Pardo, Antía S. Botana, Daniel Baldomir, PRB 86, 165114 (2012).Víctor Pardo, Antía S. Botana, Daniel Baldomir, PRB 87, 125148 (2013).
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Daniel Baldomir Antía S. Botana
Francisco Rivadulla’s group:
Paul L. BachJ.M. Vila-FungueiriñoV. Leborán
zT= σS2T/κ- Good electrical conductor- Poor heat conductor- Large thermopower
Picture taken from: Sensors and Actuators A: Physical 145-146, 423 (2008).
zT > 1 for applicationsσT/κ ~ constant for metals → S= 160 μV/K to reach zT= 1. S > 100 μV/K for a high-performance thermoelectric material
Thermoelectric figure of merit (dimensionless quantity): zT= σS2T/κ
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
- Ab initio electronic structure calculations (DFT-based)WIEN2k package.
- Full-potential, all-electron calculations.
- Comparison of three exchange-correlation potentials: GGA, LDA+U, Tran-Blaha modified version of the Becke-Jonsson potential.
- Transport properties calculated using BoltzTrap.
- We used the virtual crystal approximation to simulate doping effects.
- Structural details taken from experiment.
Methods
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Misfit layered cobaltates: NaxCoO2
High thermoelectric performanceExistence of two electronic systems
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
La2NiO4 layered compound Ni2+: d8 S=1
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
dx2
-y2
dz2
dxy
dxz,yz
J.B. Goodenough et al., Mat. Res. Bull. 17, 383 (1982).
dx2
-y2
dz2
dxydxz,yz
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
zT= σS2T/κ
σ/κ constant for metals
S2 enough to analyze trends
La2NiO4+δ
Seebeck vs. hole-doping concentration δ
T= 400 K
Peaks at about δ= 0.05 Negative thermopower at higher doping
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
Sr6Co5O15: A.S. Botana et al., PRB 83, 184420 (2011)
CrN: A.S. Botana et al., PRB 85, 235118 (2012)
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
At small hole-doping concentration, there is a peak in thermoelectric figure of merit
Figure of merit:zT= σS2T/κ
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Promising high-temperature behavior with S > 100 μV/K for δ ~ 0.05.
VCA calculations
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Calculated electronic-only figure of merit shows promising values at high T for δ ~ 0.05.Calculations do not include thermal conductivity due to phonons (largest contribution !!)
zT= σS2T/κ
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Comparison with available experiments: difficult due to lack of systematics vs. δ
- Large thermpower at low-doping- Crossing towards negative values at higher-doping levels- S increases at high T and intermediate dopings
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
zT= σS2T/κ
Using σ/κ constant from experimental valuesand S calculated.
We estimate a figure of merit zT ~ 0.1 at high T and δ ~ 0.05, can this be improved?
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
Can tensile strain improve zT ?Try to lower the energy of the x2-y2 band and utilize the localized z2 band (large S)
Valence bands get closer together when a is increased
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Values of the lattice parameter a= 3.95 – 4.00 A (tensile strain: LNO’s a= 3.86 A) leads to enlarged thermopower
zT= σS2T/κ
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Values of the lattice parameter a= 3.95 – 4.00 A (tensile strain) lead to large electronic-only figure of merit, for δ ~ 0.05 – 0.10
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Experiments confirm that tensile strain in thin films of different thicknesses (different strains) drives the system towards a larger thermopower without compromising the conductivity (in fact, decoupling them) [Paul L. Bach’s talk on Wednesday N12.12]
Summary:
• La2NiO4+δ can be a possible candidate for high-performance thermoelectric at high T if doping and strain are optimized.
• Seebeck coefficients up to 200 μV/K can be obtained above room temperature for the appropriate tensile strain.
• Conductivity and thermopower can be decoupled via strain engineering !
• Control of the stoichiometry is a new path to improve thermoelectric efficiency in oxides in general.
Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ
Víctor Pardo March Meeting, Baltimore 2013
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3-δ
Víctor Pardo March Meeting, Baltimore 2013
0 100 200 300-1000
-800
-600
-400
-200
0
0 100 200 3000
3
6
9
12
n= - 4.0 x 1016cm-3
n= - 2.7 x 1017cm-3
n= - 7.1 x 1016cm-3
n= - 2.1 x 1016cm-3
S (
V/K)
Temperature (K)
unnanealed STO
Temperature (K)
(W
/mK)
The agreement is reasonably good for the dopant concentrations analyzed (experimentally obtained via Hall effect measurements)
Very large thermopower is obtained in that very light electron doped region (as an effect in the bulk)
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3-δ
Víctor Pardo March Meeting, Baltimore 2013
Very large thermopower in STO-2DEG, really a 2D effect?
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3-δ
Víctor Pardo March Meeting, Baltimore 2013
0 100 200 300-1000
-800
-600
-400
-200
0
0 100 200 3000
3
6
9
12
n= - 4.0 x 1016cm-3
n= - 2.7 x 1017cm-3
n= - 7.1 x 1016cm-3
n= - 2.1 x 1016cm-3
S (
V/K)
Temperature (K)
unnanealed STO
Temperature (K)
(W
/mK)
STO substrates treated in order to tune the oxygen content
Very large Seebeck is observed in pure SrTiO3-δ
The effect is in a bulk (0.5 mm substrate)
See: P.L. Bach et al., arxiv/1211.1615
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3-δ
Víctor Pardo March Meeting, Baltimore 2013
We study a very light doping case, only 1 oxygen vacancy per 106 sites
We explore the very light electron-doped bulk STO via ab initio calculations
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3-δ
Víctor Pardo March Meeting, Baltimore 2013
Thermal conductivity is strongly suppressed by the introduction of scattering centers through oxygen vacancies
Similar reduction due to oxygen excess could be active for La2NiO4+δ
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3-δ
Víctor Pardo March Meeting, Baltimore 2013
La2NiO4+δ
SrTiO3-δ
i) Thin film geometry:
- large conductivity increase due to the larger in-plane conductivity- expected reduction of the thermal conductivity- will the Seebeck coefficient of thin films be different? Further calculations needed in 2D.
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
Thermoelectric properties of La2NiO4+δ from ab initio techniques
Víctor Pardo Davis, June 2012
100 200 300 400 500 600 700 8000.00E+000
5.00E+010
1.00E+011
1.50E+011
2.00E+011
2.50E+011
3.00E+011
3.50E+011
4.00E+011
a= 11.0 a.u.
a= 10.7 a.u.
S2
T (K)
a= 10.5 a.u.
La2NiO
4+= 0.05
100 200 300 400 500 600 700 8000.00E+000
5.00E+010
1.00E+011
1.50E+011
2.00E+011
2.50E+011
3.00E+011
3.50E+011
La2NiO4+= 0.10
a= 11.0 a.u.
a= 10.7 a.u.
a= 10.5 a.u.
S2
T (K)
100 200 300 400 500 600 700 8000.00E+000
5.00E+010
1.00E+011
1.50E+011
2.00E+011
2.50E+011
3.00E+011
a= 10.5 a.u., = 0.12
a= 10.7 a.u., = 0.08
a= 11.0 a.u., = 0.05
S2
T (K)
S increases as σ decresases, so we need to analyze them combined, e.g. in the form of the power factor S2σ.Highest values at the lower lattice parameter (we need to analyze compressive strain).
Thermoelectric properties of La2NiO4+δ from ab initio techniques
Víctor Pardo Davis, June 2012
100 200 300 400 500 600 700 8000
50
100
150
200
250
300
= 0.08
= 0.04
= 0.01
S_EF S_100 S_160 S_max
S (
V/K
)
T (K)
= 0.0
La2NiO
4 GGA AF tensile a= 10.7 a.u.
0.0 0.2 0.4 0.6 0.8 1.00
50
100
150
200
250
300
La2NiO
4 GGA AF tensile a= 10.7 a.u.
S (
V/K
)
p (no. holes per unit cell)
Bands become more closer together and the peak in S vs. p starts to be smeared out
Seebeck coefficients get larger (as conductivity decreases)
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
0.2 0.4 0.6 0.8 1.00
50
100
150
200
250
300
S (
V/K
)
p (no. holes per unit cell)
La2NiO
4 GGA AF tensile strain a= 11.0 a.u.
100 200 300 400 500 600 700 800
0
50
100
150
200
250
La2NiO
4 GGA AF tensile strain a= 11.0 a.u.
= 0.01
= 0.05S (
V/K
)
T (K)
= 0.0
For a sufficiently large, bands get so close together that the behavior is that of a standard semiconductor, similar to what would be obtained for CrN
Lack of intermediate-doping high S values
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
0.0 0.2 0.4 0.6 0.8 1.00
50
100
150
200
250
300
S (
V/K
)
p (no. holes per unit cell)
La2NiO
4 compressive strain a= 10.3 a.u.
100 200 300 400 500 600 700 8000
50
100
150
200
250
300
La2NiO
4 compressive strain a= 10.3 a.u.
= 0.13
= 0.15= 0.10
= 0.05
= 0.01
S (
V/K
)
T (K)
= 0.0
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
0.0 0.2 0.4 0.6 0.8 1.00
50
100
150
200
250
300
S (
V/K
)
p (no. holes per unit cell)
La2NiO
4 AF GGA a= 10.0 a.u.
100 200 300 400 500 600 700 8000
50
100
150
200
250
300
= 0.05
= 0.10
= 0.15= 0.01
La2NiO
4 AF GGA a= 10.0 a.u.
S (
V/K
)
T (K)
= 0.0
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
100 200 300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0
a= 11.0
a= 10.3
a= 11.0
a= 10.5
zT
T (K)
a= 10.7
La2NiO
4 AF GGA = 0.05
100 200 300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0
a= 10.0
a= 11.0a= 10.3
a= 10.5
a= 10.7
La2NiO
4 AF GGA = 0.10
zT
T (K)
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
100 200 300 400 500 600 700 8000.00E+000
5.00E+010
1.00E+011
1.50E+011
2.00E+011
2.50E+011
3.00E+011
3.50E+011
4.00E+011
a= 11.0 a.u.
a= 10.3 a.u.
a= 10.5 a.u.
a= 10.7 a.u.
La2NiO
4+= 0.05
S2
T (K)
100 200 300 400 500 600 700 8000.00E+000
5.00E+010
1.00E+011
1.50E+011
2.00E+011
2.50E+011
3.00E+011
3.50E+011
4.00E+011
a= 10.7, = 0.08
a= 10.5, = 0.12 a= 10.3, = 0.13
S2
T (K)
a= 11.0, = 0.05
S increases as σ decresases, so we need to analyze them combined, e.g. in the form of the power factor S2σ.Highest values at the lower lattice parameter (we need to analyze compressive strain).
100 200 300 400 500 600 700 8000.00E+000
1.00E+011
2.00E+011
3.00E+011
4.00E+011
a= 11.0 a.u.
a= 10.3 a.u.
a= 10.5 a.u.
a= 10.7 a.u.
La2NiO
4+= 0.10
S2
T (K)
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
0.0 0.2 0.4 0.6 0.8 1.00
50
100
150
200
250
300
S (
V/K
)
p (no. holes per unit cell)
La2NiO
4 AF GGA tensile strain a= 10.5 a.u.
100 200 300 400 500 600 700 8000
50
100
150
200
250
300
= 0.07= 0.12
= 0.09
= 0.01= 0.001
S (
V/K
)
T (K)
= 0.00
La2NiO
4 AF GGA tensile strain a= 10.5 a.u.
a= 3.90 Å= 10.44 a.u.a= 3.85 Å= 10.29 a.u.a= 4.00 Å= 10.69 a.u.a= 3.8 0Å= 10.16 a.u.a= 4.11 A= 11.0 a.u.
aexptal = 3.89 Å
Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δ and SrTiO3
Víctor Pardo March Meeting, Baltimore 2013
z2 ↓
x2 -y2 ↓
x2 -y2 ↑xy ↑
z2 ↑ xy ↓xz,yz
Thermoelectric properties of La2NiO4+δ from ab initio techniques
Víctor Pardo Davis, June 2012
Na cobaltates: NaxCoO2, misfits, etc …
G. Khaliullin and J. Chaloupka
Two types of electrons with different bandwidths: good conductivities and large thermpower