Tin-selenium compounds at ambient and high pressures

TL;DR

This study uses first-principles calculations to explore the structural and electronic phase transitions of tin-selenium compounds under pressures up to 100 GPa, revealing new stable phases and metalization phenomena.

Contribution

It systematically predicts pressure-induced phase transitions and stability of various Sn-Se compounds, including new metallic phases, using DFT-based crystal structure searches.

Findings

SnSe undergoes a phase transition at 2.5 GPa.

SnSe becomes metallic at 7.3 GPa.

SnSe2 metallizes above 8 GPa.

Abstract

SnxSey crystalline compounds consisting of Sn and Se atoms of varying composition are systematically investigated at pressures from 0 to 100 GPa using the first-principles evolutionary crystal structure search method based on density functional theory (DFT). All known experimental phases of SnSe and SnSe2 are found without any prior input. A second order polymorphic phase transition from SnSe-Pnma phase to SnSe-Cmcm phase is predicted at 2.5 GPa. Initially being semiconducting, this phase becomes metallic at 7.3 GPa. Upon further increase of pressure up to 36.6 GPa, SnSe-Cmcm phase is transformed to CsCl-type SnSe-Pm3m phase, which remains stable at even higher pressures. A metallic compound with different stoichiometry, Sn3Se4-I43d, is found to be thermodynamically stable from 18 GPa to 70 GPa. Known semiconductor tin diselenide SnSe2-P3m1 phase is found to be thermodynamically stable from ambient pressure up to 18 GPa. Initially being semiconducting, it experiences metalization at pressures above 8 GPa.