Cubic silicon carbide under tensile pressure: Spinodal instability

TL;DR

This study investigates the mechanical stability of cubic silicon carbide under tensile pressure using molecular dynamics simulations, identifying the spinodal point where the material becomes metastable and unstable.

Contribution

The paper provides the first detailed analysis of the spinodal instability of 3C-SiC under tensile pressure across a range of temperatures using a validated tight-binding model.

Findings

Spinodal pressure at 300K is -43 GPa.

Spinodal pressure becomes less negative with increasing temperature.

Metastability limits of 3C-SiC are mapped as a function of temperature.

Abstract

Silicon carbide is a hard, semiconducting material presenting many polytypes, whose behavior under extreme conditions of pressure and temperature has attracted large interest. Here we study the mechanical properties of 3C-SiC over a wide range of pressures (compressive and tensile) by means of molecular dynamics simulations, using an effective tight-binding Hamiltonian to describe the interatomic interactions. The accuracy of this procedure has been checked by comparing results at T = 0 with those derived from ab-initio density-functional-theory calculations. This has allowed us to determine the metastability limits of this material and in particular the spinodal point (where the bulk modulus vanishes) as a function of temperature. At T = 300 K, the spinodal instability appears for a lattice parameter about 20% larger than that corresponding to ambient pressure. At this temperature, we find a spinodal pressure P_s = -43 GPa, which becomes less negative as temperature is raised (P_s = -37.9 GPa at 1500 K). These results pave the way for a deeper understanding of the behavior of crystalline semiconductors in a poorly known region of their phase diagrams.