Structural complexity and ionic conductivity in gadolinium and tungsten co-doped La2Mo2O9: A potential electrolyte for IT-SOFCs

Gadolinium and tungsten co-substituted variants of lanthanum molybdate, characterized by the nominal formula La2-xGdxMo1.7W0.3O9-delta (x = 0.0, 0.1, 0.2, 0.3, 0.4) and denoted as LMXG, were synthesized using the Pechini method. Structural analyses employing X-ray diffraction (XRD) and angle dispersive X-ray diffraction (AD-XRD) were conducted, and the obtained data were well-fitted utilizing Rietveld refinement with the Full-Prof suite. The XRD results revealed a cubic structure with a P213 space group for both pure and co-doped LMX samples, confirming the co-dopant-induced suppression of the order-disorder phase transition temperature of LMX. Further structural investigation through AD-XRD unveiled the monoclinic structure of pure LMX, characterized by the space group P21. Raman spectroscopy provided detailed insights into the dopant-induced local restructuring within the Lanthanum molybdate lattice. Dielectric relaxation was examined through dielectric loss spectra, and AC impedance measurements were employed to extract data on ionic conductivity and activation energy. The outcomes indicated that co-doping enhances the oxy-ion conductivity compared to pure LMX. Notably, La1.7Gd0.3Mo1.7W0.3O9 (LMXG3) exhibited a higher ionic conductivity of approximately 2 x 10-2 Scm-1 at 650 degrees C, surpassing the conductivity of the pure LMX sample and other co-doped LMX variants. This investigation underscores the potential of the Gd and W co-doped LMX system as a solid electrolyte for intermediate- temperature solid oxide fuel cells (IT-SOFCs).