Bi3+/Ta5+ Co-Substitution Strategy in Lanthanide Molybdates: Achieving Ultra-Low Temperature Sintering and Enhanced Microwave Dielectric Performance in Ln₂Zr3(MoO4)9 Ceramics
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Building upon the Ln 2 Zr 3 (MoO 4 ) 9 (Ln = La, Pr, Sm, Eu, Gd) molybdate system, this study strategically employs Bi 3 ⁺/Ta 5 ⁺ co-substitution at Zr 3 ⁺ sites to achieve a remarkable enhancement in quality factor ( Q×f ), concurrently reducing optimal sintering temperatures for La- (725℃) and Sm-based (725℃) 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 exceptional microwave dielectric properties tailored by lanthanide ionic radii: La-system demonstrates ε r =10.97,Q×f = 135,333 GHz,τf=-29.74ppm/℃; Sm-system achieves ε r = 11.46, Q×f = 157,465 GHz, τf =-30.96ppm/℃; Gd-system yields ε r =11.63, Q×f = 157,280GHz, τf = -30.60 ppm/℃.Notably, sintering temperature reduction is particularly pronounced in Eu-system (675℃, ε r = 11.49, Q×f = 87,850 GHz, τf = -35.59 ppm/℃), 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℃), demonstrating significant potential for millimeter-wave communication applications.
