The dielectric constants of hot-pressed ZnO-containing 80 at. % ZnS–20 at. % SiO2 dielectric ceramics are analyzed at a frequency range varied from 1 MHz to 1 GHz. Their relative densities are controlled to range from 85 to 99% by varying the hot press pressures. A linear relationship is observed between dielectric permittivity and sintering density. The measured permittivity at 13.56 MHz frequency is found to range from 6.3 to 8.03, which is higher than the estimated values for composite materials using the Bruggeman and Lichtenecker equations. The large grain boundary area arising from nanosized grains contributes to the increase in permittivity. Additions of 0.5–5 wt % zinc oxide then increase the permittivity by forming nanosized Zn2SiO4 willemite phase on the surfaces of SiO2 particles. The presence of ZnO also stabilizes the high-temperature ZnS wurtzite phase to room temperature.

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