Effect of Sr²⁺ substitution on the sintering behavior and microwave dielectric properties of CaNd₂(MoO₄)₄ ceramics

A novel low-temperature sintering microwave dielectric ceramic CaNd₂(MoO₄)₄ was synthesized via a conventional solid-state reaction route and its microwave dielectric properties, microstructural characteristics, and chemical bond features were systematically investigated. The influence of substituting Ca²⁺ with Sr²⁺ in the specimen, denoted as Ca_1–xSr_xNd₂(MoO₄)₄ (x = 0.01 – 0.09), on the microwave dielectric properties was also studied. The CaNd₂(MoO₄)₄ ceramic exhibited a tetragonal crystalline phase with space group I41/a at a sintering temperature of 820 °C, delivering optimal microwave dielectric properties (ε_r = 10.4 ± 0.06, Q×f = 71,000 ± 2130 GHz, τ_f = −61.4 ± 4.9 ppm/°C). Moreover, limited solid solubility and a significant enhancement in microwave dielectric properties were achieved through trace Sr²⁺ substitution. The composition with x = 0.05 sintered at 850 °C exhibited the most promising performance (ε_r = 11.9 ± 0.07, Q×f = 105,000 ± 3150 GHz, τ_f = −50.9 ± 4.1 ppm/°C). Notably, Ca_1–xSr_xNd₂(MoO₄)₄ ceramics (x = 0 and 0.05) demonstrated good chemical compatibility with Ag after co-firing. Furthermore, analysis based on P-V-L bond theory and Raman spectroscopy reveals that the superior microwave dielectric properties can be primarily attributed to the dominant contribution of Ca/Nd–O bonds in lattice vibrational modes, which effectively suppress intrinsic dielectric loss. These outstanding microwave dielectric properties make the proposed ceramics highly promising candidates for high-frequency LTCC applications.