STRUCTURAL AND ELECTRONIC PROPERTIES OF α-TiNX (X:F, Cl, Br, I). AN AB INITIO STUDY

The electronic and lattice properties of alpha-TiNX (X: F, Cl, Br, I) were investigated from first principles. Ab initio calculations for geometry optimization, electronic band structure and zone-center phonon calculations have been carried out by using plane-wave pseudopotential method which is not examined before. From the electronic structure calculation, band gaps have been found as 1.23 eV, 0.955 eV, 0.897 eV for TiNF, TiNCl, TiNBr while there is no band gap for TiNI. This result can separate TiNI from other metal nitride halides which are semiconductor. Band structure calculations showed that increasing the electropositivity of halogen atom in TiNX systems decreasing the fermi energy level or in other words shift the valance bonds to higher energy. Also zone center phonon modes show that the vibrational frequencies are increasing by atomic number of halogens. Heavier halogen atom makes the system vibrate more slowly and as expected to reduce vibrational frequency.