Dielectric characteristics of doped Ba1-xSrxTiO3 at the paraelectric state

Ba1-xSrxTiO3 (x=0 to 1) ferroelectric ceramics doped with 1.0 mol.% MgO and 0.05 mol.% MnO2 were prepared with a rate-controlled sintering profile. The lattice constant of this BST system decreases as the strontium molar fraction increases. This is due to the smaller Sr2+ ionic radius than that of Ba2+. The temperature dependence of the dielectric constant is measured at 10 kHz. A linear relation of the Curie temperature of the BST system to the Sr fraction for x less than or equal to 0.75 is observed. When this reaction is fitted to a modified Curie-Weiss law, two parameters, the critical exponent and the diffuseness parameter, which represent the order of transition broadening, can be calculated. From the values of these two parameters, it is suggested that the physical meanings of these two parameters are correlated to each other. The transition broadening is greatest for x = 0.5 owing to the most composition fluctuation. Dipole relaxation of the composition with x = 0.25 is observed at frequencies above 1 MHz. On the basis of Cole-Cole analysis, a low frequency relaxation due to dopants Mn4+ at below 50 kHz is observed. (C) 1997 Elsevier Science S.A.