electronic, magnetic and thermoelectric properties of
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Electronic, Magnetic and Thermoelectric Properties ofPerovskite: BaTbO3
Dhurba Raj Jaishi1,2, and Madhav Prasad Ghimire1,2
1Central Department of Physics, Tribhuvan University, Kathmandu, Nepal2Condensed Matter Physics Research Center (CMPRC), Butwal, Nepal
Dhurba Raj Jaishi 1 / 15
Outline
1 Introduction
2 Computational Details
3 Results and Discussion
4 Conclusions
Dhurba Raj Jaishi 2 / 15
Introduction:Thermoelectric (TE) Effect
The Seebeck effect ( process thatconverts temperature gradientdirectly in to electricity).
Peltier effect (process that convertselectrical energy in to temperaturegradient).
TE performance of a materialmeasured by the figure of merit(ZT)
ZT =α2σT
κe + κl
α=8π2k2
B3eh2 m∗T( π
3n )23
Fig. 3: Schematic representation of a) Power generation and b) Cooling.
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Introduction: Requisites for Better TE Materials
Insulator
Semiconductor
Metal
Fig.1: Classification of the materials on the basis of energy gapFig.2: Schematic dependence of the electrical conductivity, Seebeckcoefficient, power factor, and thermal conductivity on the carrierconcentration (Snyder et al. Nature 7, 105-114, (2008)).
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Introduction:Perovskite
TE materials have applications:cooler, power generation,temperature sensor etc.
Silicon-Germanium, chalcogenides,Heusler alloys, Clathrates used forfabricating TE devices.
Perovskite have various interestingproperties such as:
I FerromagneticI Half-metallicI SemiconductorI Topological insulatorI Thermoelectric
Oxides Perovskite:I Structural stabilityI Low costI Naturally abundanceI Non-toxic
Fig.4: Ideal Cubic perovskite crystal structure of ABO3.
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Computational DetailsDensity functional theory (DFT) is used to study the electronic,magnetic and transport properties based on the full-potentiallinearized augmented plane wave + local orbital (FP-LAPW+lo)using generalized gradient approximation (GGA) as exchangecorrelation functional.
WIEN2K code used for the electronic/magnetic properties calculation.
BoltzTraP code to study the transport properties based on constantrelaxation time approximation (CRTA) and the rigid bandapproximation (RBA).
Dhurba Raj Jaishi 6 / 15
Crystal Structure and Optimization
Space group Pm3m (223)
a= 4.36 A, α= 90
Fig.5: Optimized crystal structure of BaTbO3.
-0.01
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
500 520 540 560 580 600 620 640 660 680
E0=-40169.175310
E-E
0 [
Ry]
Volume [bohr3]
EOS-fitCalculated energy
Fig.6: Structure optimization.
The calculated value of theenergy with respect to thevolume, fitted using theMurnaghan equation of state.
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Results and DiscussionGround state − antiferromagnetic, and direction of easy axis is foundalong [010] direction.
Table3: Total magnetic moment, spin and orbital magnetic moment of antiferromagnetic BaTbO3
Magnetic moment (µB)ms ml
GGA GGA+SOC
Total 0.0 0.0
Tb1 6.25 6.18 0.32
Tb2 -6.25 -6.18 -0.32
Fig.8: Crystal structure of antiferromagnetic BaTbO3 with direction of easy axis along [010]. The sphere in black, red, andgreen color represents Tb1, Tb2, and Ba atoms, respectively.
Dhurba Raj Jaishi 8 / 15
Results and DiscussionDensity of States
Conduction region is mainly contributed by Tb−4f orbital.Valence region is contributed by O-2p orbital near Fermi level.
-20
-10
0
10
20
a)Spin-up
Spin-down
GGA
Total
-20
-10
0
10
20
Spin-up
Spin-down
b)
Den
sity
of
stat
es (
stat
es/e
V)
Tb1Tb2
-6
-4
-2
0
2
4
6
-4 -3 -2 -1 0 1 2 3 4
Spin-up
Spin-down
c)
Energy (eV)
O-2p
d)Spin-up
Spin-down
GGA+SOC
Total
Spin-up
Spin-down
e) Tb1Tb2
-4 -3 -2 -1 0 1 2 3 4
Spin-up
Spin-down
f)
Energy (eV)
O-2p
Fig.7: Density of states.
Dhurba Raj Jaishi 9 / 15
Results and DiscussionBand Structure
0.81 eV band gap
W L Γ X W K -2
-1
0
1
2
Ener
gy(e
V)
GGA
EF
W L Γ X W K -2
-1
0
1
2
Ener
gy(e
V)
GGA+SOC
EF
Dhurba Raj Jaishi 10 / 15
Results and DiscussionTransport Properties
The Seebeck coefficientdecreases with the temperature.
σ increased with thetemperature signifiessemiconducting in nature.
200
210
220
230
240
250
260
270a)
S (
µV
K-1
)
GGA+SOC
0
5
10
15
20
25
30
35
b)
σ/τ
x 1
01
6 (
Ω c
m s
)-1
GGA+SOC
20
40
60
80
100
120
140
400 600 800 1000 1200
c)
S2σ
/τ x
10
14 (
µW
cm
-1 K
-2 s
-1)
Temperature (K)
GGA+SOC
0
0.05
0.1
0.15
0.2
0.25
400 600 800 1000 1200
d)
κe/
τ x
10
14(W
cm-1
K-1
s-1)
Temperature (K)
GGA+SOC
Fig.9: Variation of a) Seebeck Coefficient (α) b) Electrical Conductivity (σ/τ) c) Power Factor (α2σ/τ) and d) Electrical
Thermal Conductivity (κe/τ).
Dhurba Raj Jaishi 11 / 15
Results and DiscussionTransport Properties
0
20
40
60
80
100
120
140
-0.9 -0.6 -0.3 0 0.3 0.6 0.9
1200 K S
2 σ
/τ x
10
14 (
µW
cm
-1K
-2s
-1)
µ-µ0 (eV)
GGAGGA+SOC
Fig.10: Variation of the power factor with the chemical potential.
Dhurba Raj Jaishi 12 / 15
Results and DiscussionTransport Properties
Positive value of α is due to p-type charge carrier.
High value of the ZT is obtained due to the flat nature of degeneratestates in valence region near EF .
0.76
0.77
0.78
0.79
0.8
0.81
400 600 800 1000 1200
ZT
Temperature (K)
GGAGGA+SOC
Fig.11: Variation of the figure of merit (ZT) with the temperature (K).
Dhurba Raj Jaishi 13 / 15
Conclusions
We investigate the electronic, magnetic and thermoelectric propertiesusing density functional theory.
The ground-state found as antiferromagnetic with the energy gap of0.81 eV.
Large value of the Seebeck coefficient ∼ 205 µVK−1 observed even at1200 K signifies suitable for a high temperate TE devices.
Based on the CRTA, obtained value of the power factor ∼ 124 µWcm−1 K−2 at 1200 K indicates suitability for potential TE devices.
We only consider the electronic part of the thermal conductivity,lattice part is dominant over the high temperature region, whichaffect the final value of the ZT.
Dhurba Raj Jaishi 14 / 15
Acknowledgments
Central Department of Physics, Tribhuvan University, Nepal
Condensed Matter Physics Research Center (CMPRC) Butwal, Nepal
THANK YOU !!!
Dhurba Raj Jaishi 15 / 15
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