Preparation, Structure And Dielectric Properties Of Some Perovskite-Like Microwave Dielectric Ceramics

In order to explore novel high performance materials with perovskite-like structure, the preparation. Structure and dielectric properties of two B-site deficient hexagonal perovskites Ba₃LaM₃O₁₂(M=Nb,Ta) and a B-site filled hexagonal perovskite Ba₄LiNb₃O₁₂ are systematically investigated in this dissertation. The relationship between the crystal structure and dielectric properties, and the effect of composition on structure and properties of these materials are extensively investigated.At first, dielectric ceramics Ba₄iNb₃O₁₂ and Ba₃LaM₃O₁₂(M=Nb;Ta) hexagonal perovskite-related structures were prepared by the conventional solid-state reaction route. The crystal structure of new compound Ba₃LaTa₃O₁₂ was determined through Rietveld X-ray powder diffraction method using Fullprof-Suite program. Ba₄LiNb₃O₁₂ had a high ε_r of 37, a high Q·f value of 33,630GHz GHz, and a positive coefficient of resonant frequency (Ï„_f) of+89.7 ppm℃^-1; Ba₃LaNb₃O₁₂ had a ε_r of 48.3, a high Q·f value of 38,000 GHz and a low Ï„_f of - 40 ppm℃^-1, Ba₃LaTa₃O₁₂ had a ε_r, of 36.8, high Q·f value of 21,965 GHz, and low Ï„_f of - 49.6 ppm℃^-1,so they may be suitable for application as dielectric resonators.Secondly, the low-temperature firing of Ba₄LiNb₃O₁₂ ceramic was studied through the way of B₂O₃ addition. Effects of different contents of B₂O₃ on the density, microstructure and dielectric properties of Ba₄LiNb₃O₁₂ ceramic were investigated systematically as well as the mechanisms of low-temperature firing. B₂O₃ reduce the sintering temperature of Ba₄LiNb₃O₁₂ ceramic to 1000℃, this mainly resulted from the presence of liquid phase at sintering temperatures, which could accelerate the sintering. When weight percent of the addition was 1.5wt%, the ceramic presents optimal dielectric performance.Finally, multiplex oxides of 3CUO-7V₂O₅ were added to Ba₄LiNb₃O₁₂ ceramic. Studies shows that CUO-V₂O₅ could reduce the sintering temperature of Ba₄LiNb₃O₁₂ ceramic to 1100℃ since CUO-V₂O₅ formed eutectic phase at very low temperature which could accelerate the sintering.