Low-temperature sintered Mg2SiO4–CaTiO3 ceramics with near-zero temperature coefficient of resonant frequency

Abstract

The microwave dielectric properties and the microstructures of (1 − x)Mg2SiO4–xCaTiO3 composite ceramics with Bi2O3–Li2CO3–H3BO3 (BLB) additions prepared by solid-state reaction method have been investigated. The crystalline phases were studied systematically by using the X-ray diffraction, microstructures by the scanning electron microscopy and composition analysis by the energy-dispersive spectroscopy. The results showed that the τ f of (1 − x)Mg2SiO4–xCaTiO3 was related to the amount of CaTiO3 phase constitutions. When x = 0.08 and 0.09, the τ f of (1 − x)Mg2SiO4–xCaTiO3 were about −3.0 ppm/°C and +6.8 ppm/°C. The microwave dielectric properties of 0.91Mg2SiO4–0.09CaTiO3 ceramics samples with BLB additions sintered at 900–1,000 °C were characterized, and the permittivity and Q × f were associated with the amount of BLB and the sintering temperature. The sintering temperature of ceramics was reduced to 950 °C from about 1,250 °C and the temperature coefficient of resonant frequency (τ f ) was modified to −5.0 ppm/ °C with good Q × f. The addition of 12.0 wt% Bi2O3–Li2CO3–H3BO3 in 0.91Mg2SiO4–0.09CaTiO3 ceramics sintered at 950 °C showed excellent dielectric properties of e r = 7.7, Q × f = 11,300 GHz (f = 6.1 GHz) and τ f = −5.0 ppm/ °C. This represented a very promising candidate material for LTCC applications.