Preparation And Research Of Multilayer And Textured BNT-based Lead-Free Piezoelectric Ceramics

Piezoelectric ceramics are widely used in various electronic components,but the current market is mainly lead piezoelectric ceramics.At present,the working device of the field is the lead based piezoelectric ceramics,which is Harmful to human and environment.For environmental consideration,it is imperative to develop high performance lead-free piezoelectric ceramics.Bismuth sodium titanate?BNT?based lead-free piezoelectric ceramics have been widely studied as one of the materials to replace lead-based piezoelectric ceramics due to their excellent ferroelectric properties.In this paper,we aims to improve the performance of BNT-based lead-free piezoelectric ceramics,and a systematic study on BNT system has been conducted by doping modification and structural control.Taking 0.852(Bi_0.5Na_0.5)TiO₃-0.110(Bi_0.5K_0.5)TiO₃-0.038BaTiO₃?BNT-BKT-BT?as the substrate composition,the gradient doped multilayer ceramics has been obtained by doping Li.The powders of different compositions were combined at lamination process,and the multilayer ceramics were prepared by conventional ceramics sintering technique.While the multilayer ceramics showed the“temperature diffuse”effect,the temperature stability of the multilayer ceramics was greatly improved.Compared with the temperature stability parameter?TPP%?of single component ceramics,which was about 20%,the TPP%of five-layer gradient doped ceramics was only 11.6%.Meanwhile,the ferroelectric-to-relaxor transition temperature and d₃₃ value of the multilayer ceramics were between the single component ceramics with the max and min component.In addition,the multilayer ceramics are accompanied by a large electrical-strain of 0.27%to 0.31%.In this work,by doping Nb,La and Nb,the BNKST-Nb_x and BNKL_xTN_y-ST ceramics were obtained with 0.96[Bi_0.5(Na_0.84K_0.16)_0.5TiO₃]-0.04SrTiO₃?BNKT-ST?as the substrate composition.Textured ceramics were prepared by RTGG and the electro-strain response of ceramics could be enhanced with texture process.The textured BNKST-Nb₁₅ ceramics showed high electro-strain response which was improved by 43.9%and larger strain up to 0.5%@5 kV/mm(d₃₃^*=1000 pm/V)when the temperature was near the T_F-R.While there has been asymmetric strain due to grain orientation and deviation field in textured ceramics,textured BNKL₁₀TN₁₀-ST and BNKL₁₂TN₁₂-ST ceramics exhibited the best electric-field-induced strain property,with the d₃₃^* is 2364 pm/V and 1436 pm/V,respectively.Compared to the random ceramics of the same component,the d₃₃^* of textured BNKL₁₀TN₁₀-ST and BNKL₁₂TN₁₂-ST ceramics increased by 7.1-fold and2.5-fold,respectively.The development of lead-free piezoelectric ceramics is restricted by two problems of low temperature stability and low electrical strain,in this work,the two problems has been solved by gradient doped multilayer ceramics and textured ceramics,respectively.It is of great significance for the application of lead-free piezoelectric ceramics.