Dielectric permittivity dynamics of Ba1−x SrxTiO3 epitaxial films (x=0.75): Microstructure and depolarization effects

Trilayer epitaxial heterostructures including metal oxide electrodes (SrRuO3, 200 nm) and a sandwiched dielectric layer (Ba0.25Sr0.75TiO3, 700 nm) were grown by laser ablation on (001)LaAlO3 substrates. The maximum permittivity of the Ba0.25Sr0.75TiO3 layer (ɛ′/ɛ0≈3700) was obtained at T M =160 K and an external electric field E≈106 V/m. The ɛ′(T) dependence for the Ba0.25Sr0.75TiO3 layer in the paraelectric phase is well fitted by the Curie-Weiss relation, with the Curie constant and the Weiss temperature differing only insignificantly from the corresponding bulk values. The change in the permittivity of the Ba0.25Sr0.75TiO3 layer induced by the application of a ±2.5 V bias voltage to the electrodes reached as high as 85%. The electric-field dependence of the polarization retained clearly pronounced saturated hysteresis loops up to temperatures 10–15 K above T M .