Tuning the electrocaloric effect by varying Sr concentration in ferroelectric Ba1−xSrxTiO3

The electrocaloric effect is investigated systematically in ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{TiO}}_{3}$ ferroelectrics using a semiclassical direct computational approach. The data are reported for the technologically important range of Sr concentrations of 0.0--0.6, electric fields up to 1000 kV/cm, and temperatures ranging from 5 to 600 K. A detailed comparison of computational data with experimental data from the literature reveals semiquantitative agreement and suggests the origin of discrepancies. The electrocaloric change in temperature $\mathrm{\ensuremath{\Delta}}T$ shows strong dependence on Sr concentration which offers a way to tune electrocaloric response. In particular, the maximum electrocaloric $\mathrm{\ensuremath{\Delta}}T$ is found to decrease with the increase in Sr concentration, whereas the location of the maximum shifts towards lower temperatures following the Curie point of the ferroelectric. Surprisingly, the width of the peak in the dependence of $\mathrm{\ensuremath{\Delta}}T$ on the initial temperature is independent of the Sr concentration but shows a strong dependence on the applied electric field. Computational data are used to propose a compositionally graded ferroelectric ${\mathrm{Ba}}_{0.70}{\mathrm{Sr}}_{0.30}{\mathrm{TiO}}_{3}/{\mathrm{Ba}}_{0.55}{\mathrm{Sr}}_{0.45}{\mathrm{TiO}}_{3}/{\mathrm{Ba}}_{0.50}{\mathrm{Sr}}_{0.50}{\mathrm{TiO}}_{3}/{\mathrm{Ba}}_{0.45}{\mathrm{Sr}}_{0.55}{\mathrm{TiO}}_{3}$ whose $\mathrm{\ensuremath{\Delta}}T$ shows almost no temperature dependence in the technologically important range of temperatures and electric fields. Such a desirable feature could potentially lead to the enhancement of relative cooling power.