Low-Temperature Sintering Of ZnNb₂O₆ Ceramics

The low-temperature firing of ZnNb₂O₆ ceramics was studied through two ways of oxides addition and ion substitution. Effects of different oxides and V⁵+ substitution on the density, microstructure and dielectric properties of ZnNb₂O₆ ceramics were investigated systematically as well as the mechanisms of low-temperature firing. Main contents of this paper were as follows:In aspect of oxides addition, ZnNb₂O₆ ceramics were first doped with each of V2O5, Bi₂O₃, B₂O₃ which could make the Ï„f of ceramics move towards positive direction. Investigations revealed that V₂O₅ or Bi₂O₃ could reduce the sintering temperature of ZnNb₂O₆ ceramics from 1200°C only to 1050°C. Comparatively the sintering temperature of ZnNb₂O₆ doped with B2O3 could reach 975 °C The mechanism of lowering the sintering temperature with V₂O₅ was that V⁵+ went into the lattice of ZnNb₂O₆ forming substitution solid solution, which reduced the activation energy of diffusion. Because V⁵+ substituted some Nb⁵+ selectively, grain growth of ZnNb₂O₆ ceramics doped with V₂O₅ appeared directivity and sheetlike and columnar grains were resulted. Bi₂O₃ or B₂O₃ reduced the sintering temperature mainly by forming eutectic phase and introducing ion vacancy into ZnNb₂O₆ lattice. Adding Bi₂O₃ to ZnNb₂O₆ ceramics caused the ceramics generate a second phase of cubic pyrochlore BZN which agglomerated at grain boundaries restraining the grain growth of ZnNb₂O₆ While B₂O₃ was added, no new phase was. detected.On the basis of single oxide addition, multiplex oxides of V₂O₅-Bi₂O₃, V₂O₅-Bi₂O₃-CuO were added to ZnNb₂O₆ ceramics. Studies revealed that V₂O₅-Bi₂O₃ could reduce the sintering temperature of ZnNb₂O₆ to 950°C for V₂O₅ and Bi₂O₃ formed eutectic phase which could accelerate the sintering. Influenced together by V2O5 and Bi₂O₃, grain shapes of column and sheet were resulted. A small quantity of unknown phase was detected in the ceramics. Co-doping CuO with lwt%V₂O₅-lwt%Bi₂O₃ could lower the sintering temperature to 850°C because eutectic phases could be generated among CuO, V₂O₅, Bi₂O₃ and ZnNb₂O₆. The eutectic phases dispersed at the grain boundaries of ZnNb₂O₆ ceramics, which diminished the grain size.With respect to ion substitution, V⁵+, but not the traditional Ta⁵+, was used to substitute Nb⁵+. When substitution amount was within 0.05-0.15, no new phase was detected in ZnNb₂O₆ ceramics except substitution amount of 0.075 which causing the generation of Zn₃Nb₂O₈. Because of the selective substitution of Nb⁵+ by V⁵+, grains appeared columnar shape. The sintering temperature of ZnNb₂O₆ ceramics could be reduced to below 900°C with the substitution amount of 0.075 because of the second phase of Zn₃Nb₂O₈.