Study Of Properties Of Substitute Ferroelectric Ba_0.7Sr_0.3TiO₃ In A Site

Ferroelectric materials such as Barium strontium titanate (Ba_xSr_1-xTiO₃, BST) with ABO₃ type perovskite structure have gained much attention for their superior performance. They are considered as a kind of the most important materials which have great potential perspective in field of microwave,micro-electronics and memories. Nowadays, Ba_xSr_1-xTiO₃ has been recognized as one of the most ideal materials for microwave phase shift fabricating because of its high dielectric constant, lower loss tangent and remarkable nonlinear properties.In this paper, the Ba_0.7Sr_0.3TiO₃ and (Ba_0.7-xPb_x)Sr_0.3TiO₃ (x=0.1～0.4, BPST) compounds with a structure of ABO₃ were synthesized by conventional solid reaction method. Influence of Pb²⁺ substitute for Ba²⁺ in A-site on the sintering behavior and the dielectric and ferroelectric properties of BST/BPST ceramics were investigated. The X-ray diffractometry (XRD) patterns analysis reveals that the samples change from tetragonal to cubic system, and more dramatical structural distortion have been observed with the increase of Pb²⁺ concentration. The Environment Scanning Electron Microscope (ESEM) micro-graph indicate that the grain size of BST ceramics grows with the increase of sintering temperature. The smaller grain size and more compact structure of the Pb²⁺ substituted samples can be observed clearly in the ESEM graphics. The ferroelectric properties analysis shows saturated hysteresis loops of the samples when x≤0.3, which indicates the improvement of their ferroelectric properties. Compared with the ferroelectric parameters such as saturate polarization (Ps), remnant polarization (Pr) and coercive field (Ec) of BST, (Ba_0.4Pb_0.3)Sr_0.3TiO₃ has a superior performance of 15.693μC/cm², 11.300μC/cm² and 9.470 kV/cm, respectively, while the accordingly values of BST are 8.268μC/cm², 4.115μC/cm² and 2.183 kV/cm. The dielectric properties analysis reveals that the Tc increases gradually with the enhancement of Pb substitution. At room temperature, the decrease of dielectric constant becomes smaller with the Pb content increase, which i validate a relative static ferroelectric phase of the high Pb content samples. Besides, the loss tangent of the samples which are substituted by Pb²⁺ is lower than that of pure BST.