Effect of Direct-Current Biasing on the Dielectric Properties of Barium Strontium Titanate

Ba_{1− x} Sr _x TiO₃ (BST, x = 0 to x = 1) ferroelectric ceramics doped with 1.0 mol% MgO and 0.05 mol% MnO₂ were prepared with a rate-controlled sintering profile. As the strontium molar fraction x increased, the average grain size decreased from 14 μm for x = 0 to 2 μm for x = 1. Temperature dependence of the dielectric properties was measured as a function of dc biasing. At 10°C above the Curie temperature, the changes of dielectric constant at 5000 V/cm were 28%, 17%, 26%, and 36% for x = 0, 0.25, 0.5, and 0.75, respectively. The reduction of dielectric constant by the applied dc biasing was fitted by a phenomenological equation that was based on Devonshire's theory. From this phenomenological equation, an anharmonic coefficient, which was an order parameter of the anharmonic interactions, was calculated for each composition. As the strontium molar fraction increased, these coefficients increased from 2.45 × 10⁻¹⁹ cm²V⁻² for x = 0 to 5.90 × 10⁻¹⁹ cm²V⁻² for x = 0.75. A similar trend was observed on the dc field dependence of the dielectric loss, except at high field for x = 0, of which a high loss was obtained. A two-element circuit model was proposed to explain the effect of high dc biasing on the dielectric loss.