Studies On The Doping And Preparation Of BNT-Based Lead-Free Piezoelectric Ceramics

As a kind of extremely important functional materials, the piezoelectric ceramic has been found its application throughout human lives and manufacturing. Traditional PZT-based piezoelectric ceramics have been widely used for the sake of mature manufacturing process and excellent piezoelectric properties. However, the research and development of new lead-free piezoelectric ceramics has become an emergent issue of great significance in order to protect environment.Sodium bismuth titanate,(Na_0.5Bi_0.5)TiO₃(BNT)is a kind of perovskite-type ferroelectric with a relatively large remanent polarization at room temperature and a relatively high Curie temperature(Tc=320℃).For its strong ferroelectrics at room temperature, BNT has been considered to be a promising candidate material for lead-free piezoelectric ceramics.In this dissertation, the Bi_0.5(Na_1-x-yK_xLi_y)_0.5TiO₃(BNKLT) ceramics were prepared by conventional solid-state reaction method and hydrothermal synthesis. Their dielectric properties, piezoelectric properties and microstructure have been systematically studied.The content of K and Li ,phase transition and crystal structure were also mentioned. The process conditions of BNKLT are established with analyzing technologies such as sintering temperature, soaking time and polarization conditions on the dielectric and piezoelectric properties of BNKLT ceramics are investigated. The results indicate that the optium conditions of BNKLT ceramics prepared by conventional solid-state reaction method are as follows: calcining temperature 850℃, sintering temperature 1050℃,soaking time 2h, polarization field 3kV/mm and polarization time 20min; BNKLT ceramics prepared with these conditions possess outstanging dielectric and piezoelectric properties (ε/ε₀=4304.6,tanδ=6.1%,d₃₃=78pC/N). The optium conditions of Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5TiO₃ceramics prepared by hydrothermal synthesis are as follows: reaction temperature 180℃-200℃, reaction time 48h, concentration of mineralizer 8mol/L-12mol/L and sintering temperature 950℃; BNKLT ceramics prepared with these conditions possess outstanging dielectric and piezoelectric properties(ε/ε₀=3195.4,tanδ=10.46%,d₃₃=99pC/N).The properties of BNKLT ceramics prepared by hydrothermal synthesis are more excellent than by conventional solid-state reaction method. The optium formula is Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5TiO₃.