Analysis of the dielectric characteristics for polycrystalline Ba0.65Sr0.35TiO3 (II) -: d.c. field dependence with a modified bias equation

The effect of direct-current (d.c.) biasing on the dielectric properties of Ba0.65Sr0.35TiO3 (BST) with various grain sizes (0.87 mum to 5.43 mum) have been studied in the paraelectric state. The leakage current of BST samples is proportional to the biasing field. Specimens with larger grains exhibit higher leakage current under biasing. The bias equation used in the literature to predict the d.c. field dependence of permittivity is modified by introducing a bias exponent parameter beta. This modified bias equation gives a better fit to the experimental results both in this study and in the literature. Similar trends of alpha (representing the distribution of relaxation times), beta, and the variance of lattice distortion with grain sizes suggests that beta is a material parameter. It is concluded that the temperature dependence, the frequency response and d.c. field effect for the dielectric characteristics of Ba0.65Sr0.35TiO3 are all suppressed by the transition broadening. (C) 2000 Kluwer Academic Publishers.