Ca1u2013xMgxY2Ge3O10 ceramics were synthesised using the solid-state reaction method. XRD analysis reveals that the solid solubility limit of Mg2+ in Ca1u2013xMgxY2Ge3O10 lies between x = 0.15 and 0.20. Multiple characterisation approaches, including Phillipsu2013van Vechtenu2013Levine theory and bond valence analysis, were employed to systematically elucidate the crystal structure and microwave dielectric properties. TEM analysis revealed a distinct superlattice structure in the material, characterised by an increased density of (001) planes along the [100] zone axis. The presence of superlattice in Ca0.9Mg0.1Y2Ge3O10 gives rise to a higher degree of lattice ordering, thereby reducing the intrinsic loss. The corrected dielectric constant shows a trend opposite to the u03B1DT/Vm from Clausiusu2013Mossotti (Cu2013M) equation, primarily because of the rattling effect induced by Mg2+ substitution, which limits the applicability of the Cu2013M equation. The intrinsic loss of CaY2Ge3O10 was assessed by far-infrared spectroscopy. Key factors governing the microwave dielectric properties include total lattice energy (Ut), ion activation energy (Ea), and packing fraction (P.F.), which collectively determine the variation in Qu00D7f, whereas the average distortion of Yu2013O bonds (Ave(u03B4Yu2013O)), the rattling effect and proportion of Geu2013O bonds in total polarizability (u03C7(Geu2013O)/u03C7), primarily affect u03C4f. The Ca0.9Mg0.1Y2Ge3O10 ceramic exhibits an enhanced Qu00D7f, with microwave dielectric properties of u03B5r = 10.1, Qu00D7f = 106,440 GHz, and u03C4f = u221227.1 u00D7 10u22126 u2103u22121. At x = 0.15, a reduced Ave(u03B4Yu2013O), a maximum u03C7(Geu2013O)/u03C7, and a stronger rattling effect are observed, leading to a near-zero u03C4f of u22129.7 u00D7 10u22126 u2103u22121, with u03B5r = 10.3 and Qu00D7f = 91,920 GHz.
