Study On Preparation And Doping Modification Of (Na_0.5K_0.5)NbO₃Based Lead-free Ceramics

Traditional lead-based binary and polynary system piezoelectric ceramicsmaterials have many disadvantages due to high lead content. Lead-free materialdevelopment will become an inevitable trend for the improvement of peopleenvironmental protection consciousness and social sustainable development. NaNbO₃and KNbO₃formed a complete solid solution (K_0.5Na_0.5)NbO₃（KNN）, but didn’t alterit’s perovskite structure. As well, KNN has been considered as a good candidate toreplace PZT based piezoceramics because of its small dielectric constant, excellentpiezoelectric properties, high frequency constant and light density. Nowadaysmodification studies focused on sintering character and electric properties of KNNceramics system have become research hot spot. In this thesis, different content of Li⁺,Ta⁵⁺,0.90Bi_0.5Na_0.5TiO₃-0.10Bi0.5K0.5TiO₃（BNT-BKT10） and MnO₂were added toKNN based ceramics, the microstructure and electrical properties were investigated.Sol-gel method was chosed to prepare KNN based ceramics powders，ceramicswere prepared by pressureless sintering method between1020℃and1080℃，thepreparation technology was studied particularly. The result showed that, the optimumtemperature to prepare KNN ceramic powders was600℃, the relative density ofceramic samples were improved with the increase of sintering temperature, the bestsintering temperature was1060℃.All the ceramics structure kept pure perovskite structure within Li⁺and Ta⁵⁺changing content. The electric properties were improved with the increase of Li⁺content which diffused into A-site, at0.04mol Li⁺content, piezoelectric constant up to84pC/N, and relative dielectric constant up to357.45. Substituent of Nb⁵⁺with Ta⁵⁺which diffused into B-site were also discussed, the super electric properties had beenacquired at0.10mol Ta⁵⁺which was regarded as rhombohedral-tetragonamorphotropic phase boundary （MPB）, piezoelectric constant improved to93pC/N,relative dielectric constant improved to388.29.0.90Bi_0.5Na_0.5TiO₃-0.10Bi0.5K0.5TiO₃（BNT-BKT10） was added to KNN based ceramics that modified by Li⁺and Ta⁵⁺as second component, the results showed thatpiezoelectric constant was increased to99pC/N, relative dielectric constant to395.44，when the addition of BNT-BKT10was0.05mol.MnO₂was doped into the KNN matrix, and formed complete solid solutions. Thesamples with0.05mol MnO₂showed super piezoelectric constant, which up to105pC/N, relative dielectric constant decreased with the MnO₂content adding.