Effect of Mg2+ substitution on the crystal structure and microwave dielectric properties of Ca5Mn4(VO4)6 ceramics

Abstract The influence of Mg2+ substitution for Mn2+ on the crystal structure and microwave dielectric properties of Ca 5Mn4-xMgx(VO4)6 (0 ≤ x ≤ 2) ceramics was investigated. Ca5Mn4-xMgx(VO4)6 (0 ≤ x ≤ 2) ceramics were synthesized by a solid-state reaction. XRD and EDS analyses confirmed that a continuous solid solution with a garnet structure was formed for x values in the range of 0 ˜ 2. Rietveld refinement revealed that the occupation of Mn sites by Mg ions resulted in a reduction in the unit cell volume. The microwave dielectric properties closely depended on the ionic polarizability, Raman shift, packing fraction, average grain size, and bond valence. Ca 5Mn2.4Mg1.6(VO4)6 ceramics sintered at 860 °C possessed the best microwave dielectric properties of the samples considered in this study: er = 10.9, Q × f = 60,444 GHz, and τf = -76.5 ppm/°C.