Dielectric properties of Ba_1-xS_xTiO₃ films grown on LaAlO₃ substrates

We report the crystal structures and dielectric properties of barium strontium titanate, Ba_1-xSr_xTiO₃ (BST), films deposited on LaAlO₃ substrates using pulsed laser deposition, where x = 0.1 to 0.9 at an interval of 0.1. We have found that when x < 0.4 the c-axis is parallel to the plane of the substrate but normal as x approaches 1. Temperature-dependent capacitance measurements at 1 MHz show that the capacitance has a peak and that the peak temperature decreases with increasing x. We have found that the peak temperatures of the films are about 70°C higher than those of bulk BSTs when x < 0.4. From room-temperature capacitance (C) vs applied voltage (V) measurements, we have found that the C-V curves of the BST films exhibit hysteresis except for x = 0.9 and that the peak voltage at which the capacitance becomes maximum decreases with increasing x. At room temperature, the Ba_0.6Sr_0.4TiO₃ film exhibits the largest capacitance tunability (≈ 37%) with an applied electric field of 40 kV/cm.