Study On Property Of BaTiO₃-based Ferroelectric Ceramics With High Permittivity

Perovskite ABO₃ of BaTiO₃ materials have been one of more import electric materials,because of their high dielectric constant, good ferroelectric and piezoelectric properties. It have been mainly used high-capacitance multilayer capacitors, multilayer substrates, sensors and semiconductor materials. P_reparation,size effect, the temperature stability and dielectric properties of BaTiO₃–based ceramics were investiged. In recent years, with the rapid development of electronic industry and the awareness of environmental protection, more and more attention has been paid on BaTiO₃–based lead-free ceramics. In this thesis, the structure, dielectric and ferroelectric properties of Ba_1-xCa_x(Ti_0.82Zr_0.18)O₃ ceramics and (Ba_0.92Ca_0.08)(Ti_0.82Zr_0.18)O₃ ceramic doped with Nd³⁺,Y³⁺,Mn⁴⁺ have been investigated.The ceramic samples was prepared by a solid state processing and the results showed:(1) The solid solubility lay around x=0.16 for Ba_1-xCa_x(Ti_0.82Zr_0.18)O₃ ceramics and the second phase was observed when x>0.16. The changed of c/a value looks like U-type curve with the variation of the Ca²⁺, and the minimum of the c/a was 1.00276 at x=0.06. With increasing Ca²⁺ ion content, the grain size was decreased, the Curie temperature was shifted to low temperature, and theε_r-T peak was decreased and broaden. The relaxor characteristics were obtained while Ca²⁺ ion content was further increased. The value of P_r changed as the∩-type curve with the variation of the Ca²⁺ and E_c did not change significantly. The maximum of the P_r was 9.1229μC.cm^-2 at x=0.08.(2) With increasing Nd³⁺ ion content, the grain size of Ba_0.92Ca_0.08(Ti_0.82Zr_0.18)O₃ ceramics was decreased; the Curie temperature(T_c) was shifted to low temperature, and theε_r-T peak was decreased and broaden; P_r and E_c changed as the∩-type curve .With increasing Y³⁺ ion content, porosity was reduced and density was increased, the lattice constant a and c of Ba_0.92Ca_0.08(Ti_0.82-xZr_0.18 Y_x)O₃ ceramics changed as the W-type curve; Dielectric constant increased and then decreased at T_c;the maximum of the Dielectric constant was 18667 at x=0.0075. The T_c shifted to high temperature and then to low temperature. The relaxation phenomenon was observed when x≥0.0075. With increasing Y³⁺ ion content, the breakdown strength was increased and then decreased, the maximum of the breakdown strength was 6.4Kv/mm at x=0.001.(3) With increasing Mn⁴⁺ ion content, the grain size of Ba_0.92Ca_0.08(Ti_0.82Zr_0.18)O₃ ceramics was decreased; dielectric constant increased and then decreased slightly; the T_c shifted to low temperature, P_r and E_c decreased. With increasing Mn⁴⁺ ion content, T_c of Mn-doped (Ba_0.9175Ca_0.08Nd_0.0025)(Ti_0.8175Zr_0.18Y_0.0025)O₃ ceramics moved slightly to low temperature and dielectric const- ant was decreased. The relaxation behavior was gradually disappeared With increasing Mn⁴⁺ ion content. The dielectric loss changed as the U-type curve and the tanδ-T peak was broaden. Dielectric loss had reached 10^-3 when 0.0075≤x≤0.01, between -30°C¹30°C at 1KHz. P_r and E_c of ceramics were decreased.