First-principles study of thermal properties and phase transition between β-Ti ₃O ₅ and λ-Ti ₃O ₅

The first-principles density functional theory together with the quasi-harmonic Debye model is applied to investigate the thermodynamic properties and the phase transition between β-Ti ₃O ₅ and λ-Ti ₃O ₅. It is found that the phase transition from β to λ occurs only when the temperature is higher than 1420K, and at a high temperature, λ-Ti ₃O ₅ can transform to β-Ti ₃O ₅ when a proper pressure is used. The thermal properties including the bulk modulus, the molar heat capacity and the dependences of thermal expansion coefficient on temperature and pressure are also obtained in the pressure range from 0 to 20GPa and temperature range from 0 to 1500K.