EFFECT OF DIRECT-CURRENT BIASING ON THE DIELECTRIC-PROPERTIES OF BARIUM STRONTIUM-TITANATE

Ba1-xSrxTiO3 (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 si ntering profile, As the strontium molar fraction x increased, the aver age grain size decreased from 14 mu m for x = 0 to 2 mu m for x = 1, T emperature dependence of the dielectric properties was measured as a f unction of de biasing, At 10 degrees C above the Curie temperature, th e 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 die lectric constant by the applied de biasing was fitted by a phenomenolo gical equation that was based on Devonshire's theory, From this phenom enological equation, an anharmonic coefficient, which was an order par ameter of the anharmonic interactions, was calculated for each composi tion, As the strontium molar fraction increased, these coefficients in creased from 2.45 x 10(-19) cm(2).V-2 for x = 0 to 5.90 x 10(-19) cm(2 ).V-2 for x = 0.75, A similar trend was observed on the de field depen dence 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 de biasing on the dielectric loss.