First-principles Study For Electronic Structure And Physical Property Of Rutile

Titanium dioxide (TiO2), a kind of wide band gap semiconductor material, is very important and has several crystal structures, such as rutile, anatase, brookite, columbite, baddeleyite and cotunnite. TiO2is an ideal semiconductor photocatalyst and has a broad application prospect in energy materials, microelectronics and environmental protection area, due to the following advantages, for example, good catalytic activity, good stability, harmless, low cost and so on. So recently, the study on the TiO2structures, the production techniques, and physical and chemical characteristics have become a focal topic.Firstly, we study the rutile TiO2cell’s lattice constant, bulk modulus, and the first order pressure derivative of bulk modulus under the equilibrium condition, based on the first prinples of plane wave pseudopotential density functional theory. The calculated results are in good agreement with the experimental data and other calculations. To obtain the rutile’s stable structure, we calculate a series of different c/a ratios, from0.664and0.594every0.001by the software CASTEP code and fit different volume and energy. It is found that the most stable structure of rutile TiO2corresponds to the ratio c/a of about0.643.In the orther hand, the volume is calculated at different pressure, it is found the rutile TiO2can be more easily compressed when the pessure is higher.Secondly, we observe and calculate the thermodynamic properties of the rutile TiO2, for example, the expansion coefficient, the Debye temperature, heat capacity and the elasticity modulus at different temperature and pressure. It is found the heating capacity increases with the increasing temperature and decreases with elevating pressure. When the pressure and temperature are higher, due to the anharmonic Debye effect, the heating capacity is close to Dulong-Petit limit with the value of9NAkB, namely74.85J·mol-1·K-1. It also is found that as the pressure increases, the Debye temperature increases. At lower temperature, the heating expansion coefficient a increases exponentially with the temperature, while the temperature is higher, the heating expansion coefficient decreases sharply with the pressure. It can be concluded that under the high pressure and temperature condition, the heating expansion coefficient is influenced weakly with the temperature and pressure.