Microstructure and optical characterizations of mechanosynthesized nanocrystalline (Ti0.9Si0.1)N

The nanostructured (Ti0.9Si0.1)N powder has been mechanosynthesized by ball-milling the elemental stoichiometric mixture of α-Ti(0.9 mol fraction) and Si (0.1 mol fraction) powders at room temperature under nitrogen atmosphere. After 1 h of milling, the α-Ti (hcp) phase partially transformed to metastable β-Ti (cubic) phase and the initiation of (Ti0.9Si0.1)N (fcc) phase is noticed. Completely stoichiometric nanocrystalline (Ti0.9Si0.1)N phase is obtained after 7 h of milling. Microstructure of unmilled and ball-milled powders is characterized by analyzing their XRD patterns employing the Rietveld structure refinement method and by HRTEM images. The analysis reveals the inclusion of Si and nitrogen atoms into the Ti lattice on the way to formation of (Ti0.9Si0.1)N phase. Presence of Si and nitrogen in the ball milled powders is also confirmed from EDX spectra. The average size of almost monodispersed spherical particles of (Ti0.9Si0.1)N is ~ 4 nm. Optical band gaps of TiN and TiSiN powders are measured from UV–vis absorption spectra and it has been found that the optical band gap of highly insulating TiN nanoparticles (band gap ~ 5.56 eV) can be substantially reduced towards semiconductors (band gap ~ 3.96 eV) by incorporating a small amount of Si into TiN matrix.