Effects of Li Substitution and Sintering Temperature on Properties of Bi_0.5(Na,K)_0.5TiO₃ Lead-Free Piezoelectric Ceramics

Bi_0.5(Na_0.72K_0.28-xLi_x)_0.5TiO₃ (BNKLT-100x) lead-free piezoelectric ceramics are synthesized by conventional solid state sintering techniques. The dielectric and piezoelectric properties of the BNKLT-100x ceramics as a function of Li content are systematically investigated. It is found that not only Li content but also the sintering temperature has a strong effect on the piezoelectric properties of BNKLT. The piezoelectric constant d₃₃ of BNKLT varies from 120 to 252pC/N in the Li content range from 0.03 to 0.16. In the sintering temperature range from 1080 to 1130°C, the d₃₃ value of BNKLT-6 changes from 200pC/N to 252pC/N. The BNKLT-6 sample sintered at 1100°C has the highest piezoelectric constant d₃₃ of 252pC/N, with the electromechanical coupling factors k_p of 0.32 and k_t of 0.44.