Preparation Of Ca_0.4Sr_0.6Bi₄ti₄O₁₅ Ferroelectric Ceramics Textured By Templated Grain Growth

In recent years, bismuth layer- structured ferroelectrics (BLSFs), such as SrBi4Ti4O15 (SBTi), Bi4-xLaxTi3O12, and SrBi2Ta2O9(SBT) thin films, have been investigated for the applications in high-density capacitors, ferroelectric random access memories, and high temperature piezoelectric devices due to its excellent lower dielectric loss, high Curie temperature, and good fatigue-free properties on Pt electrode. These compounds belong to the Aurivillius family with a general chemical formula of (B2O2)2+(Am-1BmO3m+1)2-, where A is mono-, di- or trivalent elements with dodecahedral coordination, B is a transition cation suited to octahedral, and m is integer which presents the number of perovskite layers, their structure can be regarded as a regular intergrowth of (B2O2)2+ layers and (Am-1BmO3m+1)2-pervoskite-like slabs.Among them SrBi4Ti4O15 has high remnant polarization, lower coercive field, and good fatigue-free behavior, but the low Curi Temperature (Tc=520℃) handicaps its practical use. Recently, much attention has been paid on high temperature piezoelectric devices, higher Curie temperature materials are needed for higher temperature application. While CaBi4Ti4O15 has high Curie temperature (Tc=790℃), with the same structure of SBTi. So we did a series of experiments on replacing Sr2+ with Ca2+ of SrBi4Ti4O15 film and found that thick film exhibits good ferroelectric properties。The high anisotropic structure of BLSFs results in the ferroelectric properties to be strongly dependent on the crystallographic orientation. Templated grain growth (TGG) technique was used to obtain textured Cao.4Sro.6Bi4Ti4O15 ferroelectrics. Thus the grains of Ca0.4Sr0.6Bi4Ti4O15 film can induce the grain growth of Ca0.4Sr0.6Bi4Ti4O15 powder. In this paper, we investigated Cao.4Sro.6Bi4Ti4O15 ferroelectrics prepared by TGG technique, and its mechanism was also studied.In order to obtain oriented Ca0.4Sro.6Bi4Ti4015 templated thin film, soluble NaCl was used as the substrate of Ca0.4Sr0.6Bi4Ti4O15 thin film. Because of the solubility of NaCl, the ferroelectric thin film can be cut out completely. In our paper, oriented ferroelectric thin film was deposited on NaCl substrate, and the crystal structure and micro-morphology of Ca0.4Sr0.6Bi4Ti4O15 thin film was characterized by XRD and SEM respectively. It can be seen that the Ca0.4Sr0.6Bi4Ti4O15 ferroelectric thin films show c-axis orientation and the best preparation technique for oriented, crackles, and continuous templated thin film is rotation speed of 3250r/min, thermal decomposition temperature of 450℃, thermal decomposition time of 180s, annealing temperature of 725℃, and annealing time of 300s.Sol-gel method combined with self propagating burning was used to prepare Ca0.4Sr0.6Bi4Ti4O15 powder with well properties. In this paper, we studied the effects of gel burning time and thermal decomposition temperature on Ca0.4Sr0.6Bi4Ti4015 powder. And the crystal structure and micro-morphology of Ca0.4Sr0.6Bi4Ti4O15 powder was characterized by XRD and SEM respectively. Thus a conclusion can be drawn that 800℃is the best thermal decomposition temperature for Ca0.4Sr0.6B14Ti4O15 powder with grain size of 150nm.The Ca0.4Sr0.6Bi4Ti4O15 templated thin film cut out from NaCl substrate was pressed in Ca0.4Sr0.6Bi4Ti4O15 powder. We can get Ca0.4Sr0.6Bi4Ti4O15 ferroelectric bulks using solid phase synthesis. The induction and related mechanism of templated thin film was investigated. A conclusion can be drawn that the oriented Ca0.4Sr0.6Bi4Ti4O15 ferroelectric thin film can induce the grain growth of ferroelectric ceramic powder effectively.