A novel low loss and low temperature sintering Li3(Mg1-xCax)2NbO6 microwave dielectric ceramics by doping LiF additives

Abstract

The Li3(Mg1-xCax)2NbO6(0.02 ≤ x ≤ 0.08) ceramics were prepared through a solid-state reaction method. The effects of Ca2+ substitution for Mg2+ on the phase composition, microstructure and microwave dielectric properties of Li3(Mg1-xCax)2NbO6 ceramics were investigated systematically. The XRD results showed that all the samples remained a single Li3Mg2NbO6 phase with orthorhombic structure and Ca2+ ions could result in the expansion of unit cells when sintered at 1060–1220 °C for 6 h. In this study, the change trend of the porosity-corrected permittivity showed that the permittivity of samples was mainly relative to density, not to ionic polarizability. The variation of Q × f values also exhibited a similar trend as that of density. The τf values were in accordance with the porosity-corrected permittivity. Excellent microwave dielectric properties of εr ∼16.81, Q × f ∼122,082 GHz, τf ∼ −25.8 ppm/oC were obtained in the x = 0.04 sample when sintered at 1140 °C for 6 h. In addition, various amounts of LiF were used as sintering additive to reduce the sintering temperature in Li3(Mg0.96Ca0.04)2NbO6 ceramics. The best microwave dielectric properties of εr ∼15.85, Q × f ∼98,012 GHz, τf ∼ −28.6 ppm/oC appeared to be Li3(Mg0.96Ca0.04)2NbO6 ceramics with 6 wt% LiF sintered at 900 °C. Besides, this composition was compatible with Ag electrode, demonstrating that it could be a promising candidate material for LTCC applications.