Phase Stability of the Tin Monochalcogenides SnS and SnSe: A Quasi-Harmonic Lattice-Dynamics Study

19 August 2021, Version 3
This content is a preprint and has not undergone peer review at the time of posting.


The tin monochalcogenides SnS and SnSe adopt four different crystal structures, viz. orthorhombic Pnma and Cmcm and cubic rocksalt and π-cubic (P213) phases, each of which has optimal properties for a range of potential applications. This rich phase space makes it challenging to identify the conditions under which the different phases are obtained. We have performed first-principles quasi-harmonic lattice-dynamics calculations to assess the relative stabilities of the four phases of SnS and SnSe. We investigate dynamical stability through the presence or absence of imaginary modes in the phonon dispersion curves, and we compute Helmholtz and Gibbs free energies to evaluate the thermodynamic stability. We also consider applied pressures from 0-15 GPa to obtain temperature-pressure phase diagrams. Finally, the relationships between the different crystal phases are investigated by explicitly mapping the potential-energy surfaces along the imaginary phonon modes and by using the climbing-image nudged elastic-band method.


Tin Sulfides
Tin Selenides
Quasi-harmonic Approximation
Lattice Dynamics
Density Functional Theory
Phase Stability
Phase Diagrams
Phase Transitions


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