Curve-fitting of direct-current field dependence of dielectric constant and loss factor of Al2O3-doped barium strontium titanate

DC electric field effects on the real part of the relative dielectric constant and the loss factor of barium strontium titanate for application in phased array antennas have been studied. The real part of the relative dielectric constant of the specimens decreases with increasing applied DC field. The loss factor under bias DC electric field is slighter than the real part of the relative dielectric constant does. The tunability is about 24% for barium strontium titanate doped with 1 wt.% Al2O3 content. Variation of fitted phenomenological coefficients with Al2O3 contents below 10 wt.% is small and a rapid increase of the fitted phenomenological coefficient occurs above 10 wt.%. Variation of field coefficient A and tunability with Al2O3 contents has the same trend as that of the grain size. The real part of the relative dielectric constant of Al2O3 doped barium strontium titanate decreases rapidly before 1.0 kV cm(-1) and slowly after 1 kV cm(-1) compare to the data obtained by the curve fitting. There is a conduction loss mechanism other than the intrinsic dielectric loss for the dielectric loss under bias electric field. (C) 2000 Elsevier Science S.A. All rights reserved.