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 nitride compounds, c-Ti3N4 and c-SiTi2N4, with a spinel structure were Predicted. This result is different from the accepted model that TiNx with x>1 has a rocksalt structure with Ti vacancies. Electronic structure calculations show that these are highly covalent superhard materials, C-Ti3N4 is a narrow gap semiconductor and c-SiTi2N4 is a metal. By doping Ti at the octahedral site of the spinel c-Si3N4, the direct band gap can be adjusted. An insulator-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 promising; applications: contemplated.