High Temperature And Pressure Under The First Principle Of The Physical Properties Of ZnO

ZnO is a versatile oxide semiconductor material. It has attracted increasing interest in recent years because of its superior electronic, optical, and piezoelectric properties, leading to a wide range of applications such as light-emitting diodes, transparent field-effect transistors, ultraviolet nanolasers, solar cell and photovoltaics. Many of ZnO thin film technology compatible with integrated circuit manufacturing process, so it is able to chieve integration with silicon and other semiconductor devices. In short, ZnO has broad prospects for development.Firstly, the ab initio plane-wave pseudopotential density functional theory is employed to calculate the lattice constant, the bulk modulus and the first order pressure derivative of the bulk modulus of ZnO. Our results are in good agreement with the experimental data and other calculations. We observe that the phase transition from the wurtzite (B4) structure to the NaCl (B1) structure occurs at 10.9 GPa and the phase transition from the NaCl (B1) structure to the CsCl (B2) structure occurs at 245 GPa, which are well consistent with the calculated results by Bates and Gerward and Olsen. We also calculate the normalized volume-pressure diagram for ZnO at various temperatures.Secondly, we use the quasi-harmonic Debye model to calculate the thermodynamic properties of the ZnO. We calculate the heat capacity,the Debye temperature and the thermal expansion at different temperatures and different pressures, find that heat capacity increases with temperature increase, when T>1400K, the heat capacity approaches approximately to the Dulong-Petit result 3kB (≈49.89J·mol-1·K-1), Debye temperature increases with pressure increases. For the thermal expansion of ZnO, at low temperature, the thermal expansionαincreases with temperature increase. However, under high pressure and temperature, temperature and pressure have little effect.Finally, we study the elastic properties of ZnO. For the B4 structure of ZnO, as the pressure increases, the elastic constants C₁₁,C₁₂,C₁₃,C₃₃ increase, while C₄₄ decrease with the pressure increases. However, with the increaseing temperature, elastic constants C₁₁,C₁₂,C₁₃,C₃₃,C₄₄ are decreasing. We use the elastic constants, in accordance with the Born-Huang's stability criteria, in the usual case, ZnO of wurtzite structure, zinc-blende structure and the rock salt structure of ZnO is stable, CsCl structure is unstable under normal in high pressure stability.