Validity of rigid band approximation of PbTe thermoelectric materials

Yoshiki Takagiwa,Gregory Pomrehn,Yanzhong Pei,G Jeffrey Snyder

doi:10.1063/1.4809545

Yoshiki Takagiwa, Gregory Pomrehn + Show 2 more

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https://doi.org/10.1063/1.4809545

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Abstract

The tuning of carrier concentration through chemical doping is very important for the optimization of thermoelectric materials. Traditionally, a rigid band model is used to understand and guide doping in such semiconductors, but it is not clear whether such an approximation is valid. This letter focuses on the changes in the electronic density of states (DOS) near the valence band maximum for different p-type dopants (Na, K, Tl, or vacancy on Pb site) maintaining the high symmetry of the NaCl structure. Na- and K-doped, and vacancy-introduced PbTe show a clear rigid-band like change in DOS unlike that concluded from supercell based calculations.

Highlights

Thermoelectrics, which can generate power through the direct conversion of heat energy into electrical energy, are an attractive strategy of saving electricity from waste-heat recovery toward a solution to the global energy demands
Ahmad et al have reported the effects of hole- and electron-doping with various kinds of dopants on the electronic structure for PbTe using a supercell method based on ab initio calculation.[30]
They find that the transport properties can be significantly affected beyond that predicted by a simple rigid band approximation because the electronic density of states (DOS) in the conduction and valence bands is perturbed by dopants or defects.[30,31]

Summary

Introduction

Thermoelectrics, which can generate power through the direct conversion of heat energy into electrical energy, are an attractive strategy of saving electricity from waste-heat recovery toward a solution to the global energy demands. To test the validity of the rigid band approximation for Na- and K-doped PbTe, which has been used to explain the experimental data successfully, we calculated various amounts of doping with Na and K on Pb site, that is, up to 10% the experimental upper limit would be less than ∼2%.8,11,18 we compared with Tl-doping, which is reported to form resonant impurity states[6,9,15] in the vicinity of the valence band maximum and to exhibit superconducting properties.[40,41] we reexamined the effects of vacancy on Pb site.[30] Comparing these impurities will allow a test of the validity of the rigid band approximation for p-type doped PbTe thermoelectric material using a calculation method without changing the symmetry of the crystal structure.

Results

Conclusion