A low-εr and high-Q microwave dielectric ceramic Li2SrSiO4 with abnormally low sintering temperature. Issue 15 (December 2021) - Du, Qianbiao
Highlights: A low- εr and high- Q microwave dielectric ceramic Li2 SrSiO4 with abnormal low-temperature was investigated by PVL chemical bond theory. The weak covalency (18%) and large lattice energy of SiO bonds played a role in affecting the sintering characteristic and dielectric properties. The optimum microwave dielectric properties of Li2 SrSiO4 ceramic sintered at 880 °C were εr = 7.4 ± 0.1, Q × f = 100, 700 ± 2000 GHz, and τf = −85.4 ± 2.4 ppm/℃. Abstract: A novel low-temperature co-fired ceramic Li2 SrSiO4 with low- εr and high- Q was synthesized through solid-state reaction. XRD results showed that the Li2 SrSiO4 ceramic formed a single hexagonal structure with a space group of P 31 21. The microwave dielectric properties of Li2 SrSiO4 ceramic sintered at 880 °C were εr = 7.4 ± 0.1, Q × f = 100, 700 ± 2000 GHz, and τf = −85.4 ± 2.4 ppm/℃. The PVL chemical bond theory indicated that the low sintering temperature of Li2 SrSiO4 ceramic might be ascribed to the weak covalency (18 %) of SiO bond. A near-zero τf (‒1.9 ± 1.8 ppm/℃) combined with εr = 8.2 ± 0.1, and Q × f = 63, 200 ± 1900 GHz was obtained by adding SrTiO3 to form 0.94Li2 SrSiO4 - 0.06SrTiO3 composite ceramic. Given their chemical compatibility with Ag powders, the Li2 SrSiO4 ceramics can be a candidate dielectric material for LTCC applications.