Second-order phase transition at high-pressure in A4B6 crystals

TL;DR

This paper theoretically demonstrates a second-order structural phase transition in SnS at 16 GPa, driven by phonon mode softening, leading to a change in crystal symmetry from orthorhombic to base-centered orthorhombic.

Contribution

It provides the first theoretical evidence of a second-order phase transition in A4B6 crystals under high pressure using density-functional theory calculations.

Findings

Identified a second-order phase transition at 16 GPa in SnS.

Linked the transition to softening of a specific phonon mode.

Showed a change in crystal symmetry from Pcmn to Cmcm.

Abstract

The existence of second-order structural phase transition in the SnS at a pressure of 16 GPa has been proved theoretically. The calculation is performed using the plane-wave pseudopotential approach to density-functional theory within the local-density approximation (LDA) with the help of the ABINIT software package. The abrupt change in volume compression with unit cell volume continuous change of the crystal is the clear evidence of the second-order phase transition. It is shown that the phase transition is caused by the softening of the low-frequency fully symmetric interlayer mode with increasing pressure. As a result, displacement type phase transition (PT) take place with the change of translational symmetry of the crystal from the simple orthorhombic to the base-centered orthorhombic (Pcmn to Cmcm).