Thermal properties of Ba1−xSrxZrO3 compounds from microscopic theory

The ground-state equilibrium properties of cubic Ba1−xSrxZrO3 compounds (x = 0, 0.125, 0.25, 0.375 and 0.5) were studied by means of ab initio total energy calculations using the full-potential linearized augmented plane wave (FP-LAPW) method. In this approach, the generalized gradient approximation was used for the exchange-correlation potential. These calculations are the first step in the investigation of thermodynamics of Ba1−xSrxZrO3 compounds. We found out that compressibility decreases with the Sr concentration according to the ionic radii. The sub-stoichiometry also leads to higher hardness of perovskite compounds. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the isothermal bulk modulus, thermal expansion coefficient, specific heats at constant volume and constant pressure as well as Debye temperature were calculated. No experimental data are available and our results are considered as purely predictive. The major trends show that Ba1−xSrxZrO3 compounds tend to maintain their hardness with the temperature increases. Furthermore, the substitution of Sr2+ at Ba2+ sites in BaZrO3 has a noticeable influence on the thermal expansion behavior which makes Ba1−xSrxZrO3 compounds unable to be good candidates for application as thermal barrier coating.