Enhanced microwave dielectric properties of Y3+-substituted NaSm(MoO4)2 ceramics for LTCC applications

A series of Y 3+ -substituted NaSm 1-x Y x (MoO 4 ) 2 (x = 0.05–0.20) ceramics were synthesized via a conventional solid-state method. Y 3+ substitution significantly enhanced the microwave dielectric properties by modulating the crystal structure, microstructure, and chemical bond characteristics. Rietveld refinement confirmed that all samples adopted a single-phase tetragonal scheelite structure (space group I 4 1 /a). Lattice parameters decreased monotonically with increasing x, while the packing fraction increased from 60.80% to 61.00%, indicating lattice densification. All samples achieved relative densities exceeding 95.9%. Notably, Y 3+ doping simultaneously improved the quality factor and temperature stability: Q × f increased from 39,500 GHz to 52,400 GHz, while | τ f | decreased from 38.7 ppm/°C to 22.3 ppm/°C. The optimal properties were obtained at x = 0.20, with ε r  = 12.4, Q × f  = 52,400 GHz, and τ f  = −22.3 ppm/°C. Raman analysis revealed a negative correlation between the FWHM of the ∼886 cm −1 mode and Q × f , confirming reduced lattice anharmonicity. P–V–L bond theory demonstrated that the enhanced ionicity, lattice energy, and bond energy of the Na/Sm/Y–O bonds contributed to the improved ε r , Q × f and | τ f |, respectively. The low sintering temperature of 900 °C makes this composition highly promising for LTCC substrate applications.