First-principle calculations of the thermal properties of SrTiO3 and SrO(SrTiO3)n (n=1,2)

The thermal properties of SrTiO3 and SrO(SrTiO3)n (n=1,2) with layered perovskite structure are analyzed using the Debye–Grüneisen model combined with ab initio calculations. The thermal expansion coefficient, specific heat at constant pressure CP and specific heat at constant volume CV, adiabatic bulk modulus BS and isothermal bulk modulus BT, entropy, and Debye temperature are investigated. At temperatures higher than 550 °C, the thermal expansion coefficient and the discrepancies between CP and CV, as well as that between BS and BT, of Sr3Ti2O7 increase the fastest as the temperature rises, followed by those of Sr2TiO4, and those of SrTiO3 increase the slowest. The bulk module and Debye temperature of Sr2TiO4, Sr3Ti2O7, and SrTiO3 increase with decreasing SrO/SrTiO3 ratio at 0 K. With increasing temperature, however, the bulk modulus and Debye temperature of Sr3Ti2O7 both rapidly decrease and even fall below those of Sr2TiO4 when the temperature is higher than specific values. We also analyzed the thermal properties of these three compounds in the pressure range from 0 GPa to 16 GPa at 300 K.