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Lead-free (1-x) Bi1/2Na1/2TiO3-xKNbO3 (x=0, 0.01, 0.02, 0.04, 0.05 0.06, 0.10) piezoelectric ceramics were prepared by conventional ceramics fabrication technique. The results of x-ray diffraction (XRD) show that these ceramics possess pure perovskite structures with a symmetry transition from rhombohedral to cubic at about x = 0.05. The piezoelectric properties of these ceramics were reported and found to reach extreme values at x = 0.04 with d33 up to 113pC/N and kp up to 22%. The temperature dependence of dielectric constant and dielectric loss of these ceramics were also investigated. The Curie temperature and depolarization temperature dropped with the increase of KNbO3 amount.

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.

The effects of cerium oxide on the dielectric properties and tunable properties of barium strontium titanate/magnesia (40wt%Ba0.6Sr0.4TiO3-60wt%MgO) compound ferroelectric material for improving the properties of phase shifter were investigated. The mechanism was also presented and discussed. The XRD patterns analysis showed that with increasing quantities of cerium oxide x (wt%), the lattice constant of BST-MgO material first increased to x=0.4, then changed a little till x=1.2. Further additions of CeO2 decreased the lattice constant. The dielectric properties at 10 kHz and microwave frequency were studied. The addition of CeO2 influences the dielectric constant, loss tangent and tunability greatly. The permittivity decreased with increase of cerium oxide nearly linearly. The addition of CeO2 effectively decreased the loss in BSTM ceramic. Optimum doping amount of CeO2 reduced the high frequency loss tangents of BST-MgO compound which also ensured the moderate dielectric constant and tunability. When the doping amount of CeO2 is 1.2wt%, BST-MgO composite has the following properties: εr = 92.64, tanδ = 0.00449 (at 2.6166 GHz) and tunability = 9.67% (at 2kV/mm), it is suitable for ferroelectric phase shifter.