A novel low-temperature sintering microwave dielectric ceramic Li4SrCaSi2O8 with low-ϵr and low loss

Abstract

A novel low-temperature co-fired ceramic Li4SrCaSi2O8 with orthogonal crystal system was synthesized at 860–940 °C by the conventional solid-state reaction. The dense ceramic Li4SrCaSi2O8 features the excellent microwave dielectric properties: ϵr = 8.2, Q × f = 90,094 GHz and τf = −79.6 ppm/°C at 900 °C. Phillips–van Vechten–Levine (P–V–L) theory reveals that Si–O bond contributes 78.53% to the lattice energy for Li4SrCaSi2O8 crystal, and it was concluded that the strong ionicity (79.9%) of the Si–O bond may be responsible for the low sintering temperature of the ceramic. By compounding with CaTiO3, a near zero τf (−9.7 ppm/°C) and excellent comprehensive properties were obtained (ϵr = 9.8, Q × f = 50,145 GHz) for 0.93Li4SrCaSi2O8 + 0.07CaTiO3 ceramic at 900 °C. The chemical compatibility was confirmed by co-fired with silver, proving that Li4SrCaSi2O8 ceramic with small density is a promising candidate for LTCC dielectric materials.