Synthesis, crystal structure and microwave dielectric properties of self-temperature stable Ba1-Sr CuSi2O6 ceramics for millimeter-wave communication

Ba1-xSrxCuSi2O6 compounds with a tetrahedral structure (I41/acd) were prepared through the solid-state reaction method. The phase building process, structural evolution and microwave dielectric properties of Ba1-xSrxCuSi2O6 were investigated. Single BaCuSi2O6 phase can be obtained when calcined at 1050 °C for 3 h or 950 °C for 10 h. The substitution of Ba2+ by Sr2+ can effectively promote the sintering process and the maximum solubility of Ba1-xSrxCuSi2O6 was located between 0.25 and 0.30. Rietveld refinement, Raman-spectra and P-V-L complex chemical bond theory were used to explain the correlations between the crystal structures and microwave dielectric properties. The dielectric constant was dominated by the susceptibility (Σχμ) and ionic polarizability. The quality factor (Q × f) was determined by the bond strength, packing fraction and lattice energy, especially the Si-O bond. The susceptibility of Cu-O bond and Si-O bond played an important role in controlling the temperature coefficient of the resonant frequency (τf). A near zero τf value was obtained at x = 0–0.10 and the optimum microwave dielectric properties for Ba1-xSrxCuSi2O6 were achieved at x = 0.20 when sintered at 1000 °C for 3 h: εr = 8.25, Q × f = 47616 GHz and τf = −9.6 ppm/oC.