Thermopower in transition-metal perovskites

TL;DR

This paper derives a theoretical expression for high-temperature thermopower in transition-metal perovskites, highlighting the role of electron state degeneracy and aligning well with experimental data.

Contribution

It introduces a new theoretical formula for thermopower based on electronic structure calculations, emphasizing multiplet degeneracy over traditional spin and orbital considerations.

Findings

Derived thermopower expression matches experimental data.

Degeneracy of electron states is key to thermopower at high temperatures.

Complementary to the extended Heikes formula.

Abstract

High-temperature thermopower is interpreted as entropy that a carrier carries. Owing to spin and orbital degrees of freedom, a transition metal perovskite exhibits large thermopower at high temperatures. In this paper, we revisit the high-temperature thermopower in the perovskites to shed light on the degrees of freedom. Thus, we theoretically derive an expression of thermopower in one-dimensional octahedral-MX6-clusters chain using linear-response theory and electronic structure calculation of the chain based on the tight-binding approximation. The derived expression of the thermopower is consistent with the extended Heikes formula and well reproduced experimental data of several perovskite oxides at high temperatures. In this expression, a degeneracy of many electron states in octahedral ligand field (which is characterized by multiplet term) appears instead of the spin and orbital degeneracies. Complementarity in between our expression and the extended Heikes formula is discussed.