Density functional theory study of phase stability, vibrational and electronic properties of $Mo_3Al_2C$

TL;DR

This study uses density functional theory to analyze the phase stability, vibrational, and electronic properties of Mo_3Al_2C, revealing that carbon vacancies stabilize the structure and affect its electronic characteristics.

Contribution

It is the first to identify the stabilization of Mo_3Al_2C via carbon vacancies and estimate their concentration at experimental conditions.

Findings

Stoichiometric Mo_3Al_2C is dynamically unstable.

Carbon vacancies stabilize the structure for x > 0.09.

Estimated vacancy concentration at experimental temperatures is about 0.13-0.14.

Abstract

Based on density functional theory the noncentrosymmetric superconductor Mo_3Al_2C in its well established {\beta}-Mn type ($P4_{1}32$) crystal structure is investigated. In particular, its thermodynamical and dynamical stabilities are studied by calculating lattice vibrations within the harmonic approximation. It is found that the fully stoichiometric compound is dynamically unstable. However, compounds with carbon vacancies, i.e., Mo_3Al_2C_{1-x}, can be dynamically stabilized for vacancy concentrations x > 0.09. By means of a simple thermodynamical model we estimate x ~ 0.13-0.14 for Mo_3Al_2C_{1-x} at the experimental preparation temperatures. The influence of the carbon vacancy concentration on the electronic structure is investigated.