Anomalous dependence of thermoelectric parameters on carrier concentration and electronic structure in Mn-substituted Fe2CrAl Heusler alloy

TL;DR

This study explores how Mn substitution in Fe2CrAl Heusler alloys affects thermoelectric properties, revealing complex dependence on carrier concentration and electronic structure, with implications for high-temperature thermoelectric performance.

Contribution

It provides new insights into the anomalous dependence of thermoelectric parameters on Mn concentration and electronic structure in Fe2CrAl alloys, supported by theoretical analysis.

Findings

Mn substitution increases resistivity and Seebeck coefficient at low doping levels.

Beyond 0.25 Mn doping, both resistivity and Seebeck coefficient decrease.

Seebeck coefficient changes sign at high temperature due to hole dominance.

Abstract

We investigate the high temperature thermoelectric properties of Heusler alloys Fe2-xMnxCrAl (0<x<1). Substitution of 12.5% Mn at Fe-site (x = 0.25) causes a significant increase in high temperature resistivity (\r{ho}) and an enhancement in the Seebeck coefficient (S), as compared to the parent alloy. However, as the concentration of Mn is increased above 0.25, a systematic decrement in the magnitude of both parameters is noted. These observations have been ascribed (from theoretical analysis) to a change in band gap and electronic structure of Fe2CrAl with Mn-substitution. Due to absence of mass fluctuations and lattice strain, no significant change in thermal conductivity is seen across this series of Heusler alloys. Additionally, S drastically changes its magnitude along with a crossover from negative to positive above 900 K, which has been ascribed to the dominance of holes over electrons in high temperature regime. In this series of alloys, S and \r{ho} shows a strong dependence on the carrier concentration and strength of d-d hybridization between Fe/Mn and Cr atoms.