Crystal structure and ionic conductivity of novel rare-earth niobates LnNbO4 (Ln = Nd, Sm, Eu, Gd) by substituting Nb with W

W-substituted rare-earth niobates (LnNb(1 - x)W(x)O(4 + delta) (Ln = Nd, Sm, Eu, Gd)) have been systematically synthesized by a solid-state reaction method. Powder X-ray diffraction at room temperature revealed that the monoclinic fergusonite phase structure of unsubstituted samples gradually changes to a tetragonal scheelite phase structure with increasing W substitution. The crystal structures of the samples with x >= 0.3 can be refined well (goodness-of-fit indicator S <= 1.5) as the tetragonal scheelite structure. The W substitution improves the ionic conductivities of the four rare-earth niobates, and all of their optimum W substitution amount (x) are 0.2. The activation energy of the conductivity for the substituted samples is almost constant regardless of the type of rare-earth ion, the temperature, and the W substitution amount.

Automated summary

W-substituted rare-earth niobates with different rare-earth ions (Nd, Sm, Eu, Gd) were synthesized using a solid-state reaction method. The crystal structure of the samples gradually changed from monoclinic fergusonite phase to tetragonal scheelite phase with increasing W substitution. The ionic conductivities of all four rare-earth niobates were improved by W substitution, and the optimum W substitution amount (x) for all samples was 0.2. The activation energy of conductivity remained constant regardless of the rare-earth ion, temperature, and W substitution amount.