Dielectric relaxation in gigahertz region and phase transition of BaTiO3-based ceramics

Ba(Zr0.25Ti0.75)O-3 (BZT) and (Ba0.6Sr0.4)TiO3 (BST) ceramics were prepared as typical samples of lead-free relaxors and ferroelectrics with the diffuse phase transition, respectively. A suitable measurement technique using microplanar electrode and electromagnetic field analysis was developed to measure the microwave dielectric properties for materials with high permittivity and high dielectric loss. Frequency dependence of complex permittivity of the two ceramics was measured up to 3 GHz as a function of temperature. The dielectric dispersion of both ceramics was well explained by the stretched exponential model of the decay function in dielectric relaxation. In BST, a phase transition was observed at the permittivity peak temperature in the results of x-ray diffraction analysis, specific heat measurement, and the analysis of dielectric relaxation. The relaxation frequency of dipole fluctuation in BST was much higher than that of BZT. This high relaxation frequency enables us to use BST for dielectrics with high permittivity and low loss factors in microwave region. The continuous change from normal ferroelectrics to relaxors in BaTiO3-based ceramics was discussed. (c) 2006 American Institute of Physics.