A Study On The Lead-free Barium Strontium Titanate Based Relaxor Ferroelectric

The Barium titanate (BaTiO3) is a typically perovskite-type structure (ABO3), which has high dielectric constant value, obvious electrostrictive effec. However, the Curie temperature of BaTiO3ceramic is too high and the electrostrictive effec response slowly, which limite its using. BaTiO3-based relaxor ferroelectric ceramic are provided with high dielectric constant, the appropriate phase transition temperature and effec response smartly, etc. They are accomplished with the main materials of multilayer ceramic capacitors, but also the main materials of the theory of relaxor ferroelectrics. Therefore, the study of relaxor properties on BaTiO3ceramic has hot spots and focus.In this paper, the BaTiO3-based ceramics were doped with Sr2+, Ca2+and Nb2O5, whose stucture and dielectric properties were analysed. The main results are as follows:(1)The BaxSr1-xTiO3(BST) powders were prepared by solid state reaction and sol-gel method, respectively, The vary of Ba/Sr ratio and particle sizes’effect on the Curie Temperature and properties were analyzed. The results shows the Curie temperature increases linely with increasing Ba content, which has a line fit relation of Tc=-221.6+354x. The BST ceramics prepared by sol-gel have size effect with the dielectric peaks broaden, the dielectric constant and loss decreasing.(2) The Ba0.8Sr0.2-xCaxTiO3ceramics prepared by solid state were researched. The results show that a small amount of Ca2+substituted for Ti4+for samples x≥0.12even the (Ba+Ca+Sr)/Ti ratio value was1, which makes the grain size growth and the dielectric peak sharp. For samples x<0.12, Ca mainly enter into A sites of the perovskite instead of Ba, which leads to the grain size refinement and dielectric peak broaden. The sample(x=0.08) has relaxor behavior have maxmium y value. The value of and are1.75,2.34℃, respectively.(3) Ba0.8Sr0.12Ca0.08TiO3ceramics doping Nb2O5prepared by were characterized. The results show that adding Nb2O5contributes to the Curie tepemrature decreasing and the dielectirc obviously broaden. The sample doped with1.0mol%Nb2O5has fine relaxor behavior with low dielectirc loss and high γ value1.92. The temperature coefficient of BSCTN ceramic (x=1.0mol%) in the range from-32.75%to12.57%, which can apply to the Z7T series capatior. The BSCTN ceramic has meric relaxation properties, the△Trelax of the ceramic is7.62℃, which is close to the lead relaxor PMN (△Trelax=7.9℃).