Semi-empirical estimation of thermal expansion coefficients of perovskite-type oxides

The thermal expansion coefficients of various perovskite-type oxides have been estimated by re-evaluating the parameters used in the Ruffa's method. The Morse potential has been used to evaluate the thermal expansion coefficient assuming the Debye model for the frequency distribution of the Morse oscillator. The parameters of the Morse potential for oxides have been empirically re-evaluated, and then the thermal expansion coefficients of various perovskite-type oxides have been estimated, The calculated thermal expansion coefficients are in good agreement with the experimental ones when the main contribution to the thermal expansion is a vibrational term. In some cases, there is a difference between the calculated and experimental thermal coefficient. The difference is considered to be due to an anomalous contribution to the thermal expansion of ferroelectric or magnetic origin. From the practical point of view, the thermal expansion coefficient of four-or five-component systems is estimated by using the experimental thermal expansion coefficients of three-component systems including the anomalous contribution. The thermal expansion coefficient of four- or five-component systems is then calculated using a model similar to the regular solution model. The calculated one thus obtained better explains the experimental one than that using the ideal solution model.