Preparation And Properties Of Low Dielectric Constant Ga Based Microwave Dielectric Ceramics

Recently,some Ga-based microwave dielectric ceramics have attracted much attention due to their low dielectric constantε_r and high quality factor（Q×f）.In this thesis,the sintering behaviors,crystal structure,intrinsic loss and microwave dielectric properties of three new Mg₃Ga₂GeO₈,Mg₇Ga₂GeO₁₂ and Mg₄Ga₄Ge₃O₁₆ceramics are studied.Meanwhile,the disordered-ordered structural evolution and microwave dielectric properties of Mg_2-2x（Li Ga）_xGa₄O₈（x=0,0.25,0.50,0.6,0.65,0.75,0.85,1）spinel-structured solid solution ceramics were systematically investigated.The following results have been achieved:（1）Mg₃Ga₂GeO₈ ceramics were prepared at 1280^℃-1360^℃ by solid state reaction.XRD diffraction and Revielt refinement results showed that Mg₃Ga₂GeO₈belongs to orthogonal spinel structure with space group Imma（74）.The Mg₃Ga₂GeO₈ceramic sintered at 1340^℃ exhibited the maximum relative density of 98.94%and optimum microwave dielectric properties ofε_r=9.41,Q×f=133,113 GHz,τ_f=-63.54ppm/^℃.The distortion of octahedron of ceramics sintered at different temperature were the main the resonant frequency temperature coefficient（τ_f）.The packing fractions of ceramics sintered at different temperature were the main factor affecting quality factor.The intrinsic loss tanδ_cal of 9.934×10^-5 and intrinsic Q×f of146,325GHz（f=14.536 GHz）were obtained by fitted far infrared reflectance spectra.（2）Mg₇Ga₂Ge O₁₂ ceramics were prepared at 1300^℃-1380^℃ by solid state reaction.XRD diffraction and Revielt refinement results showed that Mg₇Ga₂Ge O₁₂belongs to orthogonal structure with space group Cmmm（65）.The Mg₇Ga₂Ge O₁₂structure also belongs to the symbiotic structure of rock salts andβ-Ga₂O₃.The Mg₇Ga₂Ge O₁₂ ceramic sintered at 1360^℃ exhibited the maximum relative density of98.44%and optimum microwave dielectric properties ofε_r=9.95,Q×f=128,371GHz,τ_f=-53.30 ppm/^℃.The packing fractions of ceramics sintered at different temperature were the main factor affecting quality factor.The intrinsic loss tanδ_cal of9.491×10^-5 and intrinsic Q×f of 141,207 GHz（f=13.402 GHz）were obtained by fitted far infrared reflectance spectra.（3）Mg₄Ga₄Ge₃O₁₆ ceramics were prepared at 1200^℃-1280^℃ by solid state reaction.XRD diffraction and Revielt refinement results showed that Mg₄Ga₄Ge₃O₁₆belongs to monoclinic structure with space group C2/c（15）.At the same time,the Mg₄Ga₄Ge₃O₁₆ structure also belongs to the symbiotic structure of spinel and pyroxene.The Mg₄Ga₄Ge₃O₁₆ ceramic sintered at 1260^℃ exhibited the maximum relative density of 98.59%and optimum microwave dielectric properties ofε_r=9.239,Q×f=87,882.94 GHz,τ_f=-58.16 ppm/^℃.The packing fractions of ceramics sintered at different temperature were the main factor affecting quality factor.The intrinsic loss tanδ_cal of 1.34×10^-4 and intrinsic Q×f of 105,447 GHz（f=14.130 GHz）were obtained by fitted far infrared reflectance spectra.（4）The Mg_2-2x（Li Ga）_xGa₄O₈（x=0,0.25,0.50,0.6,0.65,0.75,0.85,1）ceramics were prepared by solid-state reaction.XRD diffraction data and Revielt refinement data showed that superlattice diffraction peaks（110）,（210）and（211）appeared at x=0.65,indicating the transformation of the structure from a disordered cubic spinel Mg Ga₂O₄（Fd 3 m（No.227））to a cubic inverse spinel Li Ga₅O₈ with B-site 1:3ordering（P4332（No.212））.At this point,the best microwave dielectric properties were obtained:ε_r=9.39,Q×f=132,785GHz,τ_f=-51.41 ppm/^℃.Raman spectroscopy further confirmed the transition from disorder to order.As Li and Ga co-substitution for Zn,the cell volume decreases,and ionic polarizability per unit volume increases,which result in the increase of ε_r.