Phase evolution, crystal structure, and microwave dielectric properties of gillespite-type ceramics

A gillespite-structured MCuSi4O10 (M = Ba1-xSrx, Sr1-xCax) ceramics with tetrahedral structure (P4/ncc) were prepared by solid-state reaction method. X-ray diffraction and thermogravimetry with differential scanning calorimetry (TG-DSC) were employed to study the phase synthesis process of BaCuSi4O10. Pure BaCuSi4O10 phase was obtained at 1075 degrees C and decomposed into BaSiO3, BaCuSi2O6, and SiO2 when calcined at 1200 degrees C. The relationships between the crystal structure and microwave dielectric properties of MCuSi4O10 ceramics were revealed based on the Rietveld refinement and P-V-L complex chemical bond theory. The dielectric constant (epsilon(r)) decreased linearly with decreasing total bond susceptibility and ionic polarizability. Quality factor (Q x f) was closely dependent on bond strength and lattice energy. The temperature coefficient of resonant frequency (tau(f)) was controlled by the stability of [CuO4](6-) plane in MCuSi4O10. Optimum microwave dielectric properties were obtained for SrCuSi4O10 when sintered at 1100 degrees C for 3 hours with a epsilon(r) of 5.59, a Q x f value of 82 252 GHz, and a tau(f) of -41.34 ppm/degrees C. Thus, SrCuSi4O10 is a good candidate for millimeter-wave devices.

Automated summary

The gillespite-structured MCuSi4O10 ceramics with tetrahedral structure were prepared using a solid-state reaction method. The relationships between crystal structure and microwave dielectric properties were studied, revealing that the dielectric constant decreases linearly with decreasing total bond susceptibility and ionic polarizability. The quality factor was closely dependent on bond strength and lattice energy, and the temperature coefficient of resonant frequency was controlled by the stability of the [CuO4]6- plane in MCuSi4O10. Optimum microwave dielectric properties were obtained for SrCuSi4O10, making it a good candidate for millimeter-wave devices.