High-performance LTCC: Structural and microwave dielectric properties of NaLn(MoO₄)₂ (Ln = Pr, Sm)

In this work, the ultra-low loss scheelite-type Na_0.5Pr_0.5MoO₄ and Na_0.5Sm_0.5MoO₄ microwave dielectric ceramics were synthesized via the solid-state reaction method. The sintering behaviors, crystal structures, microstructures, chemical compatibility with silver electrodes, and microwave dielectric properties were systematically investigated. Both compositions exhibit good densification and chemical compatibility with silver electrodes. Na_0.5Sm_0.5MoO₄ ceramic achieves a high Q × f value of 90,900 GHz sintered at 890 °C with ε_r = 11.95, and τ_f = -45.61 ppm/°C, surpassing Na_0.5Pr_0.5MoO₄ ceramic, which exhibits Q × f = 72,600 GHz sintered at 830 °C. Raman and infrared spectroscopic analyses reveal that low-frequency phonons of [MoO₄] tetrahedra dominate the dielectric response. Sm³⁺ ions improve the packing fraction and structural symmetry of [MoO₄] tetrahedra, effectively reducing lattice defects and dielectric losses, which contributes to the superior Q × f value of Na_0.5Sm_0.5MoO₄. These findings highlight the potential of Na_0.5Sm_0.5MoO₄ ceramic as a high-performance candidate for LTCC applications.