Hafnium silicate: a new microwave dielectric ceramic with low thermal expansivity

A HfSiO4 ceramic was prepared by a conventional solid state synthesis method by sintering at 1600 degrees C. The morphology of the sintered surface was characterized using scanning electron microscopy and atomic force microscopy and the average surface roughness was about 118 nm. The sintered HfSiO4 ceramic has epsilon(r) = 7.0, Q(u) x f = 25 000 and tau(f) = -44 ppm degrees C-1 at 10 GHz. It exhibits promising thermal properties such as a low linear thermal expansivity (CTE) of -1.8 ppm degrees C-1 (dilatometer) in the temperature range of 30-800 degrees C and a room temperature thermal conductivity of 11 W m(-1) K-1.