Electronic structure and bonding properties of titanium silicides

Abstract

We present an ab initio full-potential linear muffin-tin orbital study of the structural and electronic properties of seven compounds of the binary Ti-Si system. The calculations were done with the compounds in their proposed stable structures, which are $A3\mathrm{}$ Ti, ${D8\mathrm{}}_8$ ${\mathrm{Ti}}_5{\mathrm{Si}\mathrm{}}_3$, $B27\mathrm{}$ TiSi, TiSi in distorted ${L1\mathrm{}}_0$, $C49\mathrm{}$ ${\mathrm{TiSi}}_2$, $C54\mathrm{}$ ${\mathrm{TiSi}}_2$, and $A4\mathrm{}$ Si. The calculated enthalpies of formation reproduce the observed sequence of stable structures and agree reasonably well with the values deduced from experiments. The paper ends with an analysis of the electronic structure and the bonding in the stable phases, which shows that the properties of the experimentally observed stable phases differ considerably from those of the hypothetical unstable structures. Therefore, the latter represent a poor model for the bonding in some of the stable Ti-Si compounds. We suggest that the bonding in these structures has a complex character extending beyond simple Ti-Ti and Ti-Si pairwise interactions.