Sintering behavior and microwave dielectric properties of SiO2-MgO-Al2O3-TiO2 ceramics

Sintering behavior, microstructures and microwave dielectric properties of SiO2-MgO-Al2O3-TiO2 ceramics prepared by solid state sintering method were investigated. The structure, microstructures and microwave dielectric properties of the materials were investigated by X-ray diffraction , scanning electron microscope, energy dispersive spectroscopy and network analyzer. The ceramic can be well densified after sintering at 1200 A degrees C for 3 h in air. The microwave dielectric properties are correlated with the treatment conditions. With the heat-treatment temperature is increased in the range of 1150-1250 A degrees C, the dielectric constant (epsilon(r)) of the material varies in the range of 4.5-6.25. It increases first and then decreases, with the maximum value of 6.3 appearing at 1200 A degrees C. At the same time, the quality factor (Q x f, Q = 1/tan delta, f = resonant frequency) of the material shows the similar variation, with a maximum value of 27,000 GHz appearing at 1200 A degrees C. Excellent microwave dielectric properties with a near-zero temperature coefficient of resonant frequency similar to-6.18 ppm/A degrees C, a relative permittivity similar to 6.3 and a quality factor similar to 27,000 GHz (at 9.7 GHz) was obtained.