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

Abstract

A HfSiO₄ ceramic was prepared by a conventional solid state synthesis method by sintering at 1600 °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 ε_r = 7.0, Q_u × f = 25 000 and τ_f = −44 ppm °C⁻¹ at 10 GHz. It exhibits promising thermal properties such as a low linear thermal expansivity (CTE) of −1.8 ppm °C⁻¹ (dilatometer) in the temperature range of 30–800 °C and a room temperature thermal conductivity of 11 W m⁻¹ K⁻¹.