Thermal and mechanical properties and the structural phase transition under pressure in $A$In$_2$As$_2$ ($A$ = Ca, Sr, Ba)

TL;DR

This study investigates how pressure influences the structural, mechanical, and thermal properties of AIn2As2 compounds, revealing phase transitions, anisotropy modulation, negative Poisson's ratio, and enhanced transition temperatures relevant for thermoelectric applications.

Contribution

It provides a comprehensive theoretical analysis of pressure-induced phase transitions and property modifications in AIn2As2, including symmetry analysis, mechanical anisotropy control, and phonon behavior.

Findings

Pressure induces structural phase transitions in AIn2As2.

Negative Poisson's ratio observed under compression and tension.

Pressure enhances transition temperature and affects phonon softening.

Abstract

Experimental results that BaIn2As2 and Ca(Sr)In2As2, which are the same class of alkali metal compounds, belong to different structural phases have puzzled the current materials physics community. Here, we investigate the pressure-induced structural phase transition of AIn2As2 and its accompanying improvement in mechanical and thermal properties. Firstly, the structural stability of the materials and their structural phase transitions under pressure are characterized by enthalpy and double checking by phonon dispersion spectrum. We also confirm the structural phase transitions of the hexagonal and monoclinic phases from a group-theoretic point of view, associating their symmetry operations using transformation matrices. In terms of mechanical properties, we propose an effective scheme for pressure modulation of the anisotropy of AIn2As2 materials and to induce the transformation of AIn2As2 from isotropic to anisotropic (hexagonal) and from brittle to ductile (hexagonal and monoclinic). Meanwhile, we find the negative Poisson's ratio phenomenon under compression and tension, which is favorable for a wide range of applications of this series of materials in aerospace, medicine, sensors, etc. In terms of thermal properties, applying pressure will enhance the structural phase transition temperature of AIn2As2 materials to near room temperature. We further give direct evidence of phonon softening based on group velocity calculations and reveal that phonon softening prevents the heat capacity from reaching the Dulong-Petit limit. Our study provides a theoretical basis for selecting stable structural phases and pioneering thermodynamic property studies of the thermoelectric topological candidate material AIn2As2.