Microstructure and microwave dielectric properties of CuO-modified CoWO4 ceramics

Abstract

(1 − x)CoWO4–xCuO dielectric ceramics were synthesized by the mixed oxide reaction method. W-based microwave dielectric materials with excellent properties have been reported heavily. The high sintering temperature seriously limited their commercial application in low temperature co-fired ceramics (LTCC) devices. CuO with a low melting point had been widely used as a liquid phase sintering aid. The addition of CuO had great effects on the sintering temperature, microstructure and microwave dielectric properties. When a small amount of CuO was added, the optimal sintering temperature could be decreased from 1200 to 950 °C, with no severe deterioration on the dielectric properties. The X-ray diffraction patterns indicated all samples to exhibit wolframite-like monoclinic P2/c (13) structure and no impurity phase. X-ray powder diffraction and SEM analysis revealed the formation of solutions between CoWO4 and CuO. Meanwhile, excellent microwave dielectric properties were obtained (permittivity of ~10.69, quality factor Q × f of ~20,000 GHz (f 0 = 10 GHz) and temperature coefficient of frequency τ f of ~−35 ppm/°C) for 0.97CoWO4–0.03CuO sintered at 950 °C. These features make (1 − x)CoWO4–xCuO ceramics a promising candidate for LTCC application.