Bi3+/Ta5+ Co-substitution method enabling ultra-low temperature sintering and enhanced microwave dielectric performance in Ln2Zr3(MoO4)9 lanthanide molybdates

Building upon the Ln 2 Zr 3 (MoO 4 ) 9 (Ln = La, Pr, Sm, Eu, Gd) molybdate system, this study strategically employs (Bi 0.5 Ta 0.5 ) 4+ co-substitution at Zr 4+ sites to achieve a enhancement in quality factor ( Q×f ), concurrently reducing optimal sintering temperatures for La- (725 °C) and Sm-based (725 °C) systems compared to their pristine counterparts. Comprehensive structural characterization through X-ray diffraction, Raman spectroscopy, and electron microscopy confirms the formation of phase-pure solid solutions with enhanced densification (relative density >95%), while bond valence analysis reveals that Ln-O bonds predominantly govern ionic characteristics ( f i >78%), whereas Mo-O interactions critically determine lattice energy and thermal expansion coefficients. The engineered Ln 2 [Zr 0.89 (Bi/Ta) 0.11 ] 3 (MoO 4 ) 9 ceramics exhibit microwave dielectric properties tailored by lanthanide ionic radii: La-system demonstrates εᵣ = 10.97,Q×f = 135,333 GHz,τf = −29.74 ppm/°C; Sm-system achieves εᵣ = 11.46, Q×f = 157,465 GHz, τf = -30.96 ppm/°C; Gd-system yields εᵣ = 11.63, Q×f = 157,280 GHz, τf = −30.60 ppm/°C.Notably, sintering temperature reduction is particularly pronounced in Eu-system (675 °C, εᵣ = 11.49, Q×f = 87,850 GHz, τf = −35.59 ppm/°C), attributed to the synergistic effects of bond polarizability enhancement and lattice energy optimization. These results establish a universal ion-substitution paradigm for developing advanced ULTCC materials with simultaneously improved Q×f and reduced processing temperatures (<725 °C), demonstrating significant potential for millimeter-wave communication applications. Through ion substitution, these materials all have low sintering temperatures and high Q×f values, making them ideal candidates for low-temperature co-fired ceramics (LTCC).