  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.
