Cubic silicon carbide under tensile pressure: Spinodal instability.

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 3 C -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. [Display omitted] • Cubic SiC is metastable in a large region of tensile pressure up to about 40 GPa. • Attractive region of the interatomic potential is explored for tensile stress. • Spinodal pressure is found as a function of temperature up to 1500 K. • 3C-SiC becomes an auxetic solid for a tensile pressure of 27 GPa. [ABSTRACT FROM AUTHOR]