Prediction of composition for stable half-Heusler phases from electronic-band-structure analyses

This report describes a procedure to predict the frequently occurring non-stoichiometry of the half-Heusler XYZ alloys (viz. deviations from the equiatomic 1:1:1 composition and the usually accompanied narrow homogeneity regions) from ab initio calculated electronic-band-structure characteristics. The essential feature of this approach is to utilize the valence electron content (VEC) and the calculated electronic band structure to expose factors that according to rigid-band considerations should determine the possible deviations from 1:1:1 stoichiometry and direction of the stable solid-solution regions. These means have been used to predict the direction of equilibrium solid-solution regions for a number of ternary phase diagrams that comprise half-Heusler phases and the predictions have been tested with experimental data from literature and presently synthesized and microprobe analysed samples of NiTiSn, PtTiSn, CoTiSb, PtMnSb, NiMnSb, and CoMnSb. The predictions are made based on maximum band filling of bonding states identified through the crystal-orbital-Hamilton population (COHP) analysis and density-of-states (DOS) integration.