Doping Modification Of Lead-free Capacitor Ceramics

Doping modification of lead-free ceramic （BaSr）（SnTi）O₃ with perovskite structure was carryed out, and the effects of doping on crystal structure, micro-morphology and dielectric properties were investigated to develop the ceramics with high permittivity and low temperature coefficient of capacitance.The influence of Bi³⁺、Na⁺ and Mg²⁺ on the (Ba_0.68Sr_0.32)(Ti_0.99Sn_0.01)O₃ ceramic was studied. The Curie peak (ε_max decreased and the dielectric loss increased clearly after adding Bi³⁺. The doping modification of (Ba_0.68Sr_0.311Bi_0.006(Ti_0.99Sn_0.01)O₃ ceramic with Mg²⁺ and Na⁺ showed that, the permittivity and the temperature coefficient of capacitance were reduced significantly after Mg²⁺ doped. However, Na⁺-doping resulted in rhombohedral lattice distortion, and reduced the Curie peak (ε_max, obviously optimized the dielectric loss. The study on Mg²⁺-doped (Ba0.677Sr_0.311Bi_0.006)Na_0.006(Ti_0.99Sn_0.01)O₃ ceramic indicated that, the Curie peak (ε_max decreased and the Curie temperature （Tc） shifted to lower temperature with increasing the Mg²⁺ content from 0 to 2.0mol%; the Curie peak (ε_max slightly decreases and the Curie temperature （Tc） seldom moved when the Mg²⁺ content was above 2.0mol%; additionally, when the Mg²⁺ content was above 1.0mol%, the rhombohedral lattice distortion disappeared, which could improve the dielectric loss at low temperature.Y₂O₃-first and -secondary doping modifications of (Ba_0.670Sr_0.311Bi_0.006Mg_0.010) (Ti_0.99Sn_0.01)O₃ ceramic were explored. Both Y₂O₃-first and -secondary doping modifications increased the Curie peak (ε_max, and made ceramics show evident diffused phase transition. Moreover, the Y₂O₃-first doped content affects the dielectric loss at high temperature in terms of dielectric loss. However, the Y₂O₃-secondary doping modification improved the dielectric loss at high temperature, which did not depend on Y₂O₃- secondary doped amount.(Ba_0.68Sr_0.311Bi_0.006)(Ti_0.99Sn_0.01)O₃-(Bi_0.5Na_0.5)TiO₃ ceramics were prepared via fractional step method. The ceramics showed no characteristic Curie peak (ε_max, thereby these ceramics were considered as a mixture, which consisted of compounds with different Curie temperature （Tc）. The ceramics showed excellent temperature coefficient of capacitance （TCC） at a temperature range of -25℃ 85℃. The Y₂O₃-secondary doping modification of 80wt.%(Ba_0.68Sr_0.311Bi_0.006)(Ti_0.99Sn_0.01)O₃ - 20wt.%(Bi_0.5Na_0.5)TiO₃ ceramic was studied, and the results showed that sample present high permittivity at about 3000 when Y₂O₃-secondary doped content was 0.5mol%.