Effect of carbon vacancies on structural and mechanical properties of stable zirconium carbides: A first principles study

TL;DR

This study uses first principles calculations to explore how carbon vacancies affect the structure and hardness of zirconium carbides, revealing that vacancy distribution influences mechanical properties and can be optimized with element substitution.

Contribution

The paper predicts new stable substoichiometric zirconium carbides with ordered vacancies and analyzes how vacancy distribution impacts their properties.

Findings

Carbon vacancies significantly influence volume and hardness.

Distribution of vacancies affects mechanical properties.

Replacing vacancies with nitrogen or oxygen can enhance hardness.

Abstract

By using evolutionary algorithm USPEX, we have predicted a number of stable zirconium carbides. In addition to the well-known rocksalt-type stoichiometric ZrC (Fm-3m), present prediction also identifies five stable substoichiometric zirconium carbides adopting rocksalt-type structures with ordered carbon vacancies, Zr8C7 (P-1), Zr6C5 (C2/m), Zr5C4 (P-1), Zr3C2 (C2/m), and Zr2C (Fd-3m). The effects of carbon vacancies on structural and mechanical properties are investigated. We highlight that the distribution of carbon vacancies has significant influence on volume, Pugh's ratio, and hardness. We further propose that hardness can be enhanced by replacing carbon vacancies with suitable elements, in particular nitrogen and oxygen.