Synthesis And Improvent Of High Permittivity High Frequency Ag(Nb,Ta)O₃ Ceramics

Ag(Nb,Ta)O₃ is a kind of high frequency ceramics with high permittivity. However, its temperature coefficient of permittivity and dielectric loss are large when Nb content is high, and it is difficult to be sintered when Ta content is high. In this study, Ag(Nb,Ta)O₃ ceramics was synthesized through the optimized processing route, and the effects of the Nb/Ta ratio at B-site and non stoichiometry, effects of oxide additives and the substitution of similar cations for Ag⁺ at A-site or Nb⁵⁺\Ta⁵⁺ at B-site on its crystal structure, microstructure and dielectric properties were also investigated. Some principles used for the modification of Ag(Nb,Ta)O₃ ceramics were suggested. Ag(Nb,Ta)O₃-based ceramics with good dielectric properties sintered at lower temperature were obtained. Finally, some untraditional synthesizing methods, such as semichemical or seeding method were attempted to prepare Ag(Nb,Ta)O₃.The results show that, the route that Nb2O5 and Ta2O5 firstly reacted at 1200℃, then mixed with Ag₂O and fired at 950℃, was the optimal processing route to prepare Ag(Nb,Ta)O₃ powders. With the Ta content increasing, the sintering temperature of Ag(Nb1-xTax)O₃ increased, permittivityεfirst increased and then decreased(x=0.4,εmax=516.8), dielectric loss tanδmonotonically decreased and temperature coefficient of permittivityαεshift for the negative values. The studies of non stoichiometry at B-site showed that the deficiency of (Nb,Ta) could promote Ag(Nb,Ta)O₃ sintering, but excessive (Nb,Ta) would lead to the semiconducting. Dielectric properties of Ag(Nb_0.8Ta_0.2)O₃ ceramics were greatly improved by the substitution of Na+ for Ag+ ions at A-site, which has the same valence and similar radius. When Na+ content (x) is 0.1, Ag1-xNax(Nb_0.8Ta_0.2)O₃ ceramics has the maximum permittivityεmax of 558.5 and minimum loss tanδmin of 0.0017. Similarly, proper amount of Sb(x≤0.08) substitution or Mn4+ and W6+ (x≤0.16) co-substitution for B-site Nb⁵⁺/Ta⁵⁺ ions can decrease the sintering temperature of Ag(Nb_0.8Ta_0.2)O₃, increase its permittivityε, and decrease its dielectric loss tgδ. And Sb substitution can suppress the temperature coefficient of permittivity effectively. Ag(Nb,Ta)1-xSbxO(3x=0.08)ceramics sintered at 1040℃presented optimal dielectric properties:ε=982.4 , tanδ≈0.0031 andαε=163.1ppm/℃. The dielectric loss values of Ag(Nb_0.8Ta_0.2)x(Mn,W)1-xO₃ (x=0.04, 0.08, 0.12, 0.16) ceramics, 0.00156⁰.00179, are very low and close, which indicated that a little Mn4+ and W6+ co-substitution could decrease the dielectric loss of...