DIELECTRIC CHARACTERISTICS OF DOPED BA1-XSRXTIO3 AT THE PARAELECTRIC STATE

Ba1-xSrxTiO3 (x=0 to 1) ferroelectric ceramics doped with 1.0 mol.% Mg O and 0.05 mol.% MnO2 were prepared with a rate-controlled sintering p rofile. The lattice constant of this BST system decreases as the stron tium molar fraction increases. This is due to the smaller Sr2+ ionic r adius than that of Ba2+. The temperature dependence of the dielectric constant is measured at 10 kHz. A linear relation of the Curie tempera ture 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-Wei ss law, two parameters, the critical exponent and the diffuseness para meter, which represent the order of transition broadening, can be calc ulated. From the values of these two parameters, it is suggested that the physical meanings of these two parameters are correlated to each o ther. The transition broadening is greatest for x = 0.5 owing to the m ost 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 belo w 50 kHz is observed. (C) 1997 Elsevier Science S.A.