Synthesis And Dielectric Property Of BST/BZN Dielectric Ceramics

The systhesis and dielectric property of BST-based dielectric ceramics wasstudied in this paper. A kind of voltage controlled microwave ferroelectric ceramicwas needed. The property of Ba_1-xSr_xTiO₃ was enhanced by doping BZN and Mn.yBi₂O₃-ZnO-Nb₂O₅(y=1.0)was a part of starting materials. Bi_1.5Zn_0.76Nb₁.5)O_6.8with cubic pyrochlore phase was prepared stoichiometricly. It could be sintered at880℃. Tts dielectric constant of Bi_1.5Zn_0.76Nb_1.5O_6.8 was 180(1MHz), dielectric losswas 0.9×10^-3(1MHz), and Curie temperature was +10℃. The permittivity of BZNcould change with temperature changing, this character derived from the displacementin the Bi_1.5Zn_0.76Nb_1.5O₍6.8 latter. BZN was provided with low sintering temperatureand low dielectric loss and no tunability. Curie temperature and the permittivityincreased with Bi content increasing. This is due to the content of Bi_1.5Zn_0.76Nb_1.5O_6.8increased and content of ZnNb₂O₆ and Bi₂O₃ decreased.The BST/BZN ceramics was prepared at low temperature. The phase ofBST/BZN dielectric ceramics contained cubic phase Ba_0.6Sr_0.4TiO₃ and tetrahedralphase Ba_0.5Sr_0.5Nb₂O₆. Ba_0.6Sr_0.4TiO₃ is spherical crystal and Ba_0.5Sr_0.5Nb₂O₆ isrod-shapecrystal.BST/BZN Curie temperature was +10℃. The Curie peak was broadened dueto effect of diffusion. The dielectric loss factor(1MHz) is 8.84×10^-3 and the dielectricconstant is 825, and Tunability(0.73kV/mm)=1.17%. After 1180℃sintering, thedielectric loss factor of BST/BZN ceramics decreased and Tunability(0.86kV/mm)=1.24%. Ba_0.6Sr_0.4TiO₃ is the phase of BST/BZN when the content of BZN is less.Curie temperature was lower than -40℃, and the dielectric loss factor (1MHz) is15.23×10^-3, Tunability=1.25%. The increasing of dielectric loss factor is due toZnNb₂O₆ and Bi₂O₃.The study also showed that the proper doping of Mn ions in BST could reducethe dielectric loss and dielectric constant factor. The Curie temperature could beadjusted by changing the compositions. When the Curie temperature is 0℃, theTunability is 27% and the dielectric loss factor is 3×10^-3. When the Curie temperatureis 0℃, the Tunability is 12% and the dielectric loss factor is 25×10^-4. The Tunabilityand the dielectric loss factor of the materials increase with the increase of theferroelectric phase content.