Steric effect on the M site of nanolaminate compounds M2SnC (M = Ti, Zr, Hf and Nb)

In this paper we report calculations based on an all electron ab initio full-potential linearized augmented plane-wave method using the generalized gradient approximation within the density functional theory to determine the structures of Ti2SnC, Zr2SnC, Hf2SnC and Nb2SnC. The lattice constants obtained after geometry optimization are in good agreement with experimental data. It is observed from these results that there exists a steric effect on the M site. For M atoms with atomic radius (Zr, Hf) larger than that of tin, the polyhedra (octahedron and trigonal prism) constituting the unit cell are less distorted compared to those related to M atoms with atomic radius (Ti, Nb) similar to that of tin. The computed values for the bulk modulus of these ternary carbides are predicted to be about 69% of those of the corresponding binary carbides MC. The analysis of the projected local density of states shows that the major hybrids come from M (M = Ti, Zr, Hf, Nb) d and C p states.