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Al2O3 ceramics with CaO-SiO2-MgO (CMS), Yb2O3 and ZrO2 additives were fabricated by a conventional solid-state reaction method. The effects of ZrO2 dopant on phase compositions, microwave dielectric properties and dielectric breakdown strength of Al2O3 ceramics were studied. XRD demonstrated that CaAl2Si2O8 and Zr &Y compound phases co-existed with alumina. SEM exhibited that ZrO2 dopant could refine the grain of alumina ceramics and improve its relative density. With ZrO2 content increasing from 1wt% to 5wt% εr increased from 9.8 to 10.25, but Q×f decreased from 52823GHz to 35922GHz. The breakdown strength increased initially and reached the maximum value at ZrO2=3wt%. When ZrO2 content is 3wt%, the comprehensive performances were the best: Eb= 37.37kV/mm for 1mm samples and 17.26kV/mm for 3mm samples, Q×f = 37044 GHz, εr = 10.01, and τf = -52 ppm/°C.

Yttrium aluminum garnet Y3Al5O12 (YAG) nanopowders were synthesized from co-crystallized precursors of Y2(SO4)3, Al(NO3)3-Al2(SO4)3 and Y(NO3)3 with a three-layer core-shell structure. X-ray diffraction (XRD) pattern indicated that too much was detrimental to the synthesis of pure phase YAG because of the serious separation between Y2(SO4)3 and Al(NO3)3-Al2(SO4)3. Transmission electron microscopy (TEM) revealed that was beneficial for the dispersion of the powders owing to the high decomposition temperature of . The powders with the n()/n(Y3+) mole ratio of 1.5/3 calcined at 1050°C showed good sintering activity.