Non-linear Dielectric Characteristic And Ferroelectrics Phase Transition Of (Ba_1-xCa_x)(Ti_1-ySn_y)O₃ Ceramics

Recently, field tunable dielectrics have been extensively studied due to their important applications in the field tunable devices such as voltage-controlled oscillators, tunable filters and phase shifters. In these applications, both high tunability (=[ε(0)-ε(E)]/ε(0)) and low dielectric loss are required. The currently most studied materials are perovskite SrTiO₃ (ST), (Ba,Sr)TiO₃ (BST) and Ba(Zr,Ti)O₃ (BZT). In order to explore potential candidates for field tunable dielectric materials, the present work is focused on the microstructures and the nonlinear dielectric properties of A- and B- site substituted barium titanate ceramics. In order to obtain high non-linear dielectric tunability near room temperature, the BaTiO₃ based solution were modified with Ca²⁺and Sn⁴⁺ to decrease dielectric loss and shift the Curie temperature.The cubic perovskite structure is obtained for (Ba_1-xCa_x)(Ti_1-ySn_y)O₃ (x = 0.05, 0.1 y = 0.05, 0.10, 0.15 and 0.20) solid solution. With increasing Sn content, the peak of dielectric constant and dielectric loss move to the lower temperature. The Sn content and T_m fit a linear relationship. For (Ba_0.95Ca_0.05)(Ti_1-ySn_y)O₃ and (Ba_0.95Ca_0.05)(Ti_1-ySn_y)O₃, the maximum dielectric constant (ε_m) at T_m increases with increasing Sn content firstly and then decreases. The substitution of Ca does not change the T_m of (Ba_1-xCa_x)(Ti_1-ySn_y)O₃ distinctly. A small quantity of Ca can increase the dielectric constant and decrease the dielectric loss at the room temperature. Ca/Sn co-substitution shifts the T_m of (Ba_1-xCa_x)(Ti_1-ySn_y)O₃ ceramics towards the room temperature.(Ba_0.95Ca_0.05)(Ti_1-ySn_y)O₃ ceramics exhibit excellent dielectric tunability under the DC bias. When y = 0.15, the tenability at 10kHz is as high as 35.4% under a relative low electric-field (2.0kV/cm). It keeps 24.1% at the room temperature and above 20% in a broader rang around the room temperature. When the frequencies are 100kHz and 1MHz, the tenability keeps between 40-50% at the room temperature. The T_m of (Ba_1-xCa_x)(Ti_1-ySn_y)O₃ towards the room temperature with increasing Ca content. According to the Devonshire theory and the experiment data, higherdielectric tubability of (Bao.9Cao.i)(Tii.ySny)03 (y = 0.05, 0.10, 0.15 fP 0.20) ceramics will be obtained at room temperature.With increasing Sn content, the (Bai-xCax)(Tii.ySny)O3 ceramics show the enhanced DPT (diffuse phase translation) and relaxor behaviors. When the content of Sn keeps the same, the DPT and relaxor behavior will be shown more clearly. The DPT and ralexor existing in (Bai.xCax)(Tii.ySny)O3 benefit for the tunability and temperature coefficient.