Crystal structure, chemical bond characteristics and microwave dielectric properties of low-permittivity Ca1–xMgxY2Ge3O10 ceramics with superlattice

Ca 1– x Mg x Y 2 Ge 3 O 10 ceramics were synthesised using the solid-state reaction method. XRD analysis reveals that the solid solubility limit of Mg 2+ in Ca 1– x Mg x Y 2 Ge 3 O 10 lies between x = 0.15 and 0.20. Multiple characterisation approaches, including Phillips–van Vechten–Levine 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 Ca 0.9 Mg 0.1 Y 2 Ge 3 O 10 gives rise to a higher degree of lattice ordering, thereby reducing the intrinsic loss. The corrected dielectric constant shows a trend opposite to the from Clausius–Mossotti (C–M) equation, primarily because of the rattling effect induced by Mg 2+ substitution, which limits the applicability of the C–M equation. The intrinsic loss of CaY 2 Ge 3 O 10 was assessed by far-infrared spectroscopy. Key factors governing the microwave dielectric properties include total lattice energy ( U t ), ion activation energy ( E a ), and packing fraction ( P.F. ), which collectively determine the variation in Q×f , whereas the average distortion of Y–O bonds (Ave( δ Y–O)), the rattling effect and proportion of Ge–O bonds in total polarizability ( χ (Ge–O)/ χ ), primarily affect τ f . The Ca 0.9 Mg 0.1 Y 2 Ge 3 O 10 ceramic exhibits an enhanced Q×f , with microwave dielectric properties of ε r = 10.1, Q×f = 106,440 GHz, and τ f = −27.1×10 –6 °C –1 . At x = 0.15, a reduced Ave( δ Y–O ), a maximum χ (Ge–O)/ χ , and a stronger rattling effect are observed, leading to a near-zero τ f of −9.7×10 –6 °C –1 , with ε r = 10.3 and Q×f = 91,920 GHz.