Preparation Of Barium Strontium Titanate(Ba_1-xSr_xTiO₃) Ceramics With High Dielectric Properties

Barium strontium titanate(BST) ceramic is an entirely solid solution of barium titanate and strontium titanate. It has received extensive attentions because of their predominant properties, such as high dielectric constant and flexoelectric coefficients, low dissipation factor and adjustable Curie temperature. Therefore, Ba1-x Srx TiO3 ceramic are of great research significance.BST ceramic powders were prepared by high temperature solid-state reaction. Three doping formulations were made, respectively was xmol%Y3+-Ba0.65Sr0.35TiO3, xmol%Y3+(x=0, 0.3)-Ba1-xSrx TiO3(x=0.4, 0.35 and 0.3) and 1wt%B2O3-xmol%Y3+-Ba0.65Sr0.35TiO3 ceramics. All samples were prepared by dry pressing molding and sintering. By X-ray diffraction, SEM and impedance analyzer, the crystal structure, surface morphology and dielectric properties of the BST ceramics were analyzed.It was found that all samples of xmol%Y3+ and 1wt%B2O3-xmol%Y3+ doped Ba0.65Sr0.35TiO3 consist of single phase of perovskite. Doping with 0.3mol%Y3+ or 1wt%B2O3 could promote grain growth, the former grain size increased from 1? m to 2-3?m, and the latter was increased from 1?m to 4-7?m. With the increase of the doping amount, the grain growth was inhibited. After doping with 1wt%B2O3, the inhibition phenomenon was more significant. Appropriate increase of the sintering temperature can increase the dielectric constant. With the increase of the Y3+ content, the dielectric constant had a maximum value, the dielectric loss had a minimum value. The dielectric constant of the all samples varied with the frequency(100-10MHz) were firstly decreased slowly, then stabilized and finally a sharp downward trend, the dielectric loss firstly decreased and then increased. It was found that the higher the dielectric constant, the larger the transverse flexoelectric coefficient. The relative density of 0.3mol%Y3+-Ba0.65Sr0.35TiO3 sintered in 1450 ? was 95.1%, which had the maximum dielectric constant(17811) and the minimum dielectric loss(0.00869). The Curie temperature was 21?, and the transverse flexoelectric coefficient was 27.9?C/m.All samples of Ba1-x Srx TiO3 ceramics(x=0.4, 0.35 and 0.3) doped with xmol%Y3+(x=0, 0.3) had formed a solid solution. With the increase of Ba/Sr ratio, the grain size and the dielectric constant increased at the same Y3+ doping amount. After doping with 0.3mol%Y3+, the porosity and the dielectric loss decreased, density and the dielectric constant increased at the same Ba/Sr ratio. The sample of 0.3mol%Y3+-BST70 had maximum dielectric constant(27811) while the sample of 0.3mol%Y3+-BST65 had minimum dielectric loss(0.00869). With the increase of frequency from 100 Hz to 10 MHz, it was found that the dielectric constant decreased, the dielectric loss was stable at low frequency and increased dramatically at high frequency. The sample of 0.3mol%Y3+-BST65 had the best frequency stability of dielectric constant. In the test temperature(-100?-100?) range, the dielectric constant had a maximum value. The dielectric constant peak temperature(TC) increased almost linearly with the increase of Ba/Sr ratio. After doping with Y3+, the C urie temperature shifted to lower temperature when Ba/Sr was 0.6/0.4. The transverse flexoelectric coefficient of the sample 0.3mol%Y3+-BST70 was maximum(33.68?C/m).