Disclosing the behavior under hydrostatic pressure of rhombohedral MgIn2Se4 by means of first-principles calculations

Abstract

AM₂X₄ crystalline materials display important technological electronic, optical and magnetic properties that are sensitive to general stress effects. In this paper, the behavior under hydrostatic pressure of the ambient condition rhombohedral phase of MgIn₂Se₄ is investigated in detail for the first time. We carried out first-principles calculations within the density functional theory framework aimed at determining the pressure-induced polymorphic sequence of this selenide. To accurately evaluate transition pressures at room temperature, thermal corrections have been included after the computation of phonon dispersion curves in potential candidate phases, namely the initial rhombohedral Rm one, inverse and direct spinels, LiTiO₂-type and defective I structures. Only the transition from the Rm to the inverse spinel phase was found to fulfill the thermodynamic and mechanical stability criteria. The direct spinel could appear as metastable if kinetic effects hinder the above transition. Additionally, electronic band structures and chemical bonding properties were analyzed from the outcome of our quantum-mechanical solutions reporting band gap values and ionicity and noncovalent interaction indexes. It is shown that the investigated compound keeps behaving as a semiconductor, loses its van der Waals interactions, and becomes more covalent as hydrostatic pressure is applied.