Preparation, Structure And Dielectric Properties Of A₄B₃O₁₂ Microwave Dielectric Ceramics

The aim of the thesis is to explore and develop promising new niobate dielectric function materials. With the high speed development of modern communication, the trend to miniaturization, high frequency and integration of mobile communication system intensively requires research and development new dielectric function ceramics.Firstly, on the basis of the characteristic of filled layered perovskite-like structure with the general formula A₄B₃O₁₂, a series of new niobates Ba_3-xLa_1+xTi_xNb_3-xO₁₂ ( Ba₃LaNb₃O₁₂ , Ba₂La₂TiNb2O₁₂, BaLa₃TiNb₂O₁₂ ) were designed in the thesis, and prepared by high temperature solid-state reaction technique (all calcined at 1350℃ for 10h; Ba₃LaNb₃O₁₂ was sintered at 1440℃ for 6h ,Ba₂La₂TiNb₂O₁₂ was sintered at 1440℃ for 6h, BaLa₃Ti₂NbO₁₂ was sintered at 1460℃ for 6h). The ceramics were characterized by X-ray powder diffraction (XRD), Raman, Scanning Electron Microscope (SEM), density analysis and chemical analysis. The results show that these ceramics are all single-phase, with A4B3O12 hexagonal perovskite structure; the indexed XRD data of Ba₃LaNb₃O₁₂ and refined unit cell parameters were a=5.7552(3) A, c=28.15(2) A, Z=3, V=806.87.04(9) A³, and theoretical density is 6.310 g·cm^-3 ;the indexed XRD data of Ba₂La₂TiNb₂O₁₂ and refined unit cell parameters were a=5.7623(2) A, c=27.740(2)A, Z=3 , V=773.04(9)A3, and theoretical density is 6.305 g·cm-3.and unit cell parameters of BaLa₃Ti₂NbO₁₂ were a=5.6128 (2) A, c=27.0813 (2)A, Z=3, V=738.86(5)A3, and theoretical density is 6.303 g·cm^-3 The dielectric properties of them show that: Ba₃LaNb₃O₁₂, Ba₂La₂TiNb₂O₁₂ and BaLa₃Ti₂NbO₁₂ ceramics have dielectric constant of 44.86, 42.70 and 42.42. temperature coefficients of resonance frequency (Ï„_f) are-40ppm/℃, -4.2ppm/℃, +6ppm/℃, which is much close to zero respectively., and they are promising to be a new type of dielectric ceramics.