Ionic conduction in substituted scheelite-type oxides

In a search for new high temperature ionic conductors, various substituted scheelite-type samples were prepared by the solid state reaction and their electrical conduction was investigated. Typical scheelite-type oxides designated as ABO4 (A=Ca, Sr, Ba; B=W, Mo) are generally classified into the oxysalts. However, some oxides having cations with almost the same electronegativities, such as Pb and W in PbWO4, can be regarded as double oxides with a deformed fluorite-type structure. Therefore, in order to create appropriate conductors in each oxide type, A2+B6+O4, alternative substitutions were tried: A1−xM+2xBO4 for the former and A1−xM3+xBO4+x/2 for the latter. As a result, new types of ionic conductors were found: lithium ion conductors and oxide ion conductors in scheelite-type solid solutions based on ABO4 (A=Ca, Sr, Ba; B=W, Mo) and PbWO4, respectively. Lithium ion conduction was confirmed visually by neutron radiography.