# First-principles investigations of orthorhombic-cubic phase transition and its effect on thermoelectric properties in cobalt-based ternary alloys

## TL;DR

This study uses first-principles calculations to explore phase stability and thermoelectric properties of cobalt-based ternary alloys, revealing potential new cubic phases with promising thermoelectric performance.

## Contribution

It identifies energetically favorable cubic phases in certain cobalt-based alloys and links covalent interactions to phase stability, aiding the search for efficient thermoelectric materials.

## Key findings

- Ge-group alloys favor cubic symmetry energetically
- Transport properties of most systems surpass CoTiSb
- Estimated figure of merit exceeds that of CoTiSb

## Abstract

We screened six cobalt-based 18-VEC systems CoVSi, CoNbSi, CoTaSi (Si-group) and CoVGe, CoNbGe, CoTaGe (Ge-group) by the first-principles approach, with the motivation of stabilizing these orthorhombic phases into the cubic symmetry -- favorable for thermoelectrics. Remarkably, it was found that the Ge-group is energetically more favorable in the cubic symmetry than the hitherto orthorhombic phase. We account the cubic ground state of the Si-group to the interplay of internal pressure and covalent interactions. The principle of covalent interactions will provide an insight and could be vital in speeding the search of missing cubic half-Heusler alloys. Meanwhile, the calculated transport properties of all the systems on \textit{p}-type doping, except CoVSi, are more promising than the well-known CoTiSb. We also provide conservative estimates of the figure of merit, exceeding the CoTiSb. Based on our findings, we suggest possible new phases of ternary compounds for thermoelectric applications.