Stability, electronic, magnetic and thermoelectric properties of quaternary Heusler alloys CoX'ZrAl (X'=V, Fe, Ir): 3d vs 5d systems

TL;DR

This study investigates the electronic, magnetic, and thermoelectric properties of quaternary Heusler alloys CoX'ZrAl (X'=V, Fe, Ir) using DFT and Boltzmann theory, identifying CoVZrAl as a promising thermoelectric material with high ZT.

Contribution

The paper provides a comprehensive first-principles analysis of three CoX'ZrAl alloys, revealing their magnetic states and thermoelectric potential, especially highlighting CoVZrAl's high ZT value.

Findings

CoVZrAl is semiconducting with high thermoelectric efficiency.

CoFeZrAl is non-magnetic with high electrical conductivity.

CoIrZrAl exhibits half-metallic behavior with reduced thermoelectric performance.

Abstract

The thermoelectric (TE) properties of quaternary Heusler alloys (CoX'ZrAl; X'= V, Fe, Ir) are studied in the framework of Density Functional Theory and Boltzmann Transport Theory. The compound CoVZrAl is found to be semiconducting and the most difficult to be formed whereas the easier formed newly-predicted CoFeZrAl and CoIrZrAl are pseudo-gapped and half-metal respectively. Ferromagnetic calculations show magnetism in CoVZrAl and CoIrZrAl originating from the non-bonding Co-X' fully-filled t1u state and partially-filled eu state derived from Co-3d and X'-3d and 5d electrons respectively while CoFeZrAl is non-magnetic. The two-dimensional graphene-like density of states at the Fermi level in CoFeZrAl implies large electrical conductivity. We further observe that the presence of two 3d early Transition metal (TM) atoms enhances the Seebeck coefficient as in CoVZrAl and CoFeZrAl and the presence of extended 5d state of Ir diminishes the same for CoIrZrAl. However the higher thermal conductivity in CoFeZrAl renders CoVZrAl the best TE material among the three. The ZT value of n-type CoVZrAl is found to reach a higher value 1.4 at 600 K.