Study On The Synthesis And Properties Of Soft Chemical Derived BMT-PT Based High-T_c Piezoelectric Ceramics

At present, traditional PbZrO3-PbTiO3(PZT)-based ceramics and their binary, ternary systems are widely used as piezoelectric materials. However, PZT ceramics contain more than60wt%lead, which causes environment pollution during processing, preparing, using, and disposing. Lead-free ceramics have become a hot research topic in the world, but they have not yet replaced the conventional PZT piezoelectric ceramics due to the limitations in the piezoelectric and ferroelectric properties. In addition, the operating temperature of most commercial piezoelectric ceramics is limited to half of the Curie temperature, about150℃, restricting the application in high temperature fields. Therefore, the development of new types of piezoelectric ceramics with less lead and high Curie points system is imperative.As a new type of high temperature piezoelectric system, BMT-PT ceramics have attracted much attention due to their high Curie temperature and good piezoelectric ferroelectric properties. This system is relatively easy for the industrialization and exhibits a good prospect of the application, so it has been selected for the study.A sol-gel soft chemical route was used to prepare0.63BMT-0.37PT powders in this study, which own high purity and compositional uniformity. A focus was then on the mechanism of hydrolyze and polymerization and the structural evolution in xerogel at various heat-treat temperatures. The results indicated that the gel can be transformed into superfine crystalline powders with a single perovskite using a heat-treatment temperature at600℃for3hours, which is200℃lower than the calcination temperature in a solid state method. Because well-dispersed superfine powders own a good sintering activity, the0.63BMT-0.37PT ceramics can be well densified at temperatures50℃lower than those via a mixed-oxide method, and the metal ions can be mixed at real molecular level. All of which enhance the piezoelectric properties of d33～230pC/N, kp～30%, Tc=463℃and ε33T=1208.Because0.63BMT-0.37PT ceramics have a few disadvantages such as relatively high conductivity, lower d33and high coercive field Ec, etc., Mn3+and Nb3+were used to improve their electrical properties. The0.63BMT-0.37PT+nMn3 ceramics with a pure perovskite structure have been successfully synthesized by a citrate sol-gel method. The substitution of the manganese ions tend to produce a certain amount of oxygen vacancies, which can reduce the activation energy of mass transfer in the sintering processing, thus promoting the sintering density. The conductivity and coercive field are increased with increasing the content of Mn3+but the d33and Pr values are reduced by the domain pinning, resulting from the formation of O2-vacancies. The phase structures of0.63BMT-0.37PT+xNb3+ceramics have been changed from a typical rhombohedral-tetragonal coexisted structure to a nearly pure rhombohedral structure, and a small amount of Nb3+can improve the densification. The dielectric maxima and Tc value were obviously suppressed due to the Nb5+addition. The piezoelectric properties could be slightly improved as a small amount of Nb3+was doped, acting as a soft additive. The0.63BMT-0.37PT+0.5%Nb5+ceramics exhibit improved electrical properties of d33～245pC/N and kp～30%.