Microwave dielectric properties of LiM(PO3)3 (M = Mg2+, Zn2+) ceramics

Abstract

Microwave dielectric ceramics with low dielectric permittivity εr combined with low ceramic sintering temperatures have raised considerable research interest recently due to their potential application in LTCC technology for 5G wireless communications. Here in this study, ceramic processing, crystal structure, and microwave dielectric properties of LiM(PO3)3 (M = Mg2+, Zn2+) ceramics were comprehensively investigated. Optimized LTCC compatible ceramic sintering processes were developed at 725 °C and 625 °C for 10 h, respectively, leading to high relative densities of 96.27 % and 94.09 %. Low microwave εr values of 5.74 and 6.30 and Q × f values of 16,660 GHz and 9629 GHz (at 14 GHz) were obtained, where such values were found to be affected by the grain microstructure. LiMg(PO3)3 exhibited a small τf of −11 ppm/°C, while LiZn(PO3)3 showed −58 ppm/°C. Complementary impedance spectroscopy measurements indicated modest Li+-ion conductivity with a higher value of 2.92·10−7 (Ωcm)−1 at 560 K (287 °C) in LiZn(PO3)3. Both ceramics were found to be dielectrically homogeneous without any perceptible contributions from the grain boundaries.