Synthesis and Study of Electrical Transport Properties of Composite Solid Electrolytes MWO4–SiO2 (M = Ca, Sr) and Ln2W3O12–SiO2 (Ln = La, Nd)

Composite solid electrolytes based on alkaline earth tungstates MWO4–SiO2 (M = Ca, Sr) and rare-earth metal tungstates Ln2W3O12–SiO2 (Ln = La, Nd) with the addition of nanosized silica were synthesized. Their morphology, thermal, structural, and ionic transport properties were investigated. The absence of thermal effects in DSC measurements of tungstate–silica mixtures, as well as the lack of reflections from any secondary phases in the diffraction patterns of the composites, confirms their thermodynamic stability. The ionic nature of conductivity in the studied composites was demonstrated by high ionic transference numbers (0.8–0.9, obtained using the EMF method) and the absence of dependence of conductivity on oxygen partial pressure in the gas phase. The concentration dependence of conductivity in the composites (1–x)MWO4–xSiO2 (M = Ca, Sr) and (1–x)Ln2W3O12–xSiO2 (Ln = La, Nd) exhibits a maximum at x = 0.03–0.30 (x being the molar fraction). The highest conductivity (3.2 × 10–2 S/cm) at 900°C was observed in the composite 0.70Nd2W3O12–0.30SiO2.