Ab initio study of Nb 2SC and Nb 2S 2C: Differences in coupling between the S and Nb–C layers

Abstract

Using ab initio calculations, we have studied the structurally related compounds Nb 2SC and Nb 2S 2C. In Nb 2S 2C (space group R 3 ¯ m , prototype Bi 2Te 3), S atoms are nearest neighbours, while in Nb 2SC (space group P6 3/ mmc, prototype Cr 2AlC) this is not the case. The calculated equilibrium volume for these two phases deviates by 1.6–3.7% to previously-published experimental data and the bulk modulus-to- c 44 ratios obtained are 1.5 and 5.9, respectively. These results indicate a resemblance of Nb 2S 2C to hexagonal BN and graphite. Furthermore, we have demonstrated that the uniform compression method is adequate for estimating the elastic properties of Nb 2SC, a so-called MAX phase. It is our ambition that these calculations will stimulate further experimental research on these compounds.