The phase transitoons of tio2 compound under high pressure: AB Initio phase stability

In this study, phase transition of TiO2 under high pressure was studied by using AB initio technique and Generalized Gradient approach. Siesta simulation program was used in the study. The applied pressures were increased in 10 GPa increments and the symmetry of the structure was observed in 20 GPa. It was observed that symmetry changed from tetragonal rutile (P42/mnm) structure to othorhombic Pmn21 structure using this Kplot package program. The parameters of rutile unit cell parameters were a = 4,6056 Å, b = 4,6056 Å, c = 2,9788 Å and Pmn21 unit cell parameters were also a = 2,9004 Å, b = 4,3773 Å, c = 4,5336Å. When the pressure was increased to 30 GPa, the structure changed again and it was observed that the orthorhombic Pmn21 structure passed to the baddeleyite (P21/c) structure and the unit cell parameters were found as a= 4,7365 Å, b= 4,6035 Å, c= 4,8923Å. In addition, enthalpy calculations were made using the Birch-Murnaghan state equation method and the phase transition was obtained from the pressure-enthalpy graph around 11 GPa. It was found to be around 12 GPa in experimental studies. As a result, it was observed that the obtained values were consistent with the previous experimental and theoretical studies.