Two novel low-firing germanates Li 2 MGe 3 O 8 (M = Ni, Co) microwave dielectric ceramics with spinel structure

Abstract Two low-firing ceramics Li 2 MGe 3 O 8 (M = Ni, Co) were prepared using the solid state reaction method and their microwave dielectric properties were characterized. X-ray diffraction analysis showed that both ceramics crystallized into a cubic spinel structure. Both ceramics were well densified at temperatures lower than 960 °C. Li 2 NiGe 3 O 8 ceramic sintered at 940 °C with relative density of ~95.2% obtained the optimum microwave dielectric properties with a relative permittivity ( e r ) ~8.6, a quality factor ( Q×f ) ~42,200 GHz (at 12.2 GHz), a temperature coefficient of resonance frequency τ f ~ −78.2 ppm/°C. For Li 2 CoGe 3 O 8 , the ceramic sintered at 950 °C had a relative density of 95.4%, a e r of 9.0, a Q×f of 40,500 GHz (at 12.6 GHz) and a τ f of −42 ppm/°C. The negative τ f values could be tuned by forming composite ceramics with rutile TiO 2 . Chemical compatibility measurement indicates that both ceramics did not react with silver.