Prediction of the new spinel phase of Ti3N4, and SiTi2N4 and the metal-insulator transition

Titanium nitrides are important materials with many industrial applications . However, the structure and properties of nitrogen-rich compounds are hot well established. Based on ab initio calculations, stochiometric titanium n itride compounds, c-Ti3N4 and c-SiTi2N4, with a spinel structure were Predi cted. This result is different from the accepted model that TiNx with x>1 h as a rocksalt structure with Ti vacancies. Electronic structure calculation s show that these are highly covalent superhard materials, C-Ti3N4 is a nar row gap semiconductor and c-SiTi2N4 is a metal. By doping Ti at the octahed ral site of the spinel c-Si3N4, the direct band gap can be adjusted. An ins ulator-to-metal transition in c-Si[Si1-xTix](2)N-4 is predicted to occur at x=0.44. A process of preparing these compounds is suggested, and several p romising; applications: contemplated.