Nonlinear dielectric response of c- and a-axis oriented epitaxial (Ba,Sr)TiO₃ layers between metallic oxide electrodes

Abstract
Trilayer epitaxial heterostructures of SrRuO₃/(700nm)Ba_xSr_1-xTiO₃/SrRuOx₃ (x= 0.25 ; 0.8) have been grown by laser ablation on (001)LSATO. Both ferroelectric and oxide metallic layers in the trilayer heterostructure possess granular structure. The grains (100-200 nm) in the ferroelectric layer were well in-plane and out-of-plane oriented and separated by low angle grain boundaries. Orientation of the polar axis in the ferroelectric layer was dependent on the type of mechanical stresses (tensile or compressive). When in paraelectric state, Ba_xSr_l-xTiO₃ layers followed a Curie - Weiss behavior with Weiss temperature and Curie constant roughly matching those of a bulk single crystal. The dielectric constant of the c-axis oriented Ba_0.25Sr_0.75TiO, layers was tuned in the range 3700ε0 - 450ε0 if +/- 2.5V if a bias voltage between +2.5V and -2.5V was applied to the electrodes. The loss factor, tan δ for the ferroelectric layers peaked at temperatures below the phase transition point. The peak falls at lower temperature at lower frequency and is affected by a bias voltage.