Synthesis and examination of GdNb1-xWxO4+δ new scheelite-type oxide-ion conductor

Abstract

Synthesis of a novel solid solution system GdNb1-xWxO4+δ through substituting W for Nb has been investigated by a solid-state reaction method. It is found that the structure of the system changed from a monoclinic fergusonite phase to a tetragonal scheelite phase with increasing W substitution and that a single tetragonal scheelite phase could be obtained at room temperature with the composition of 0.3 ≤ x ≤ 0.7. The structural phase transition temperature decreases with increasing W substitution and the tetragonal scheelite phase can be stabilized by the W substitution, as reveals by Synchrotron powder X-ray diffraction. The conductivity of GdNbO4 is significantly improved by the substitution of W for Nb and that of GdNb1-xWxO4+δ (0.4 ≤ x ≤ 0.6) samples reach 10−5 S cm−1 at an intermediate temperature of 600 °C. The activation energy of the conductivity for the substituted samples is almost constant regardless of the temperature and the W substitution amount.