Electrotransport in tungstates Ln2(WO4)3 (Ln = La, Sm, Eu, Gd)

A number of methods were used to study the electrical properties of lanthanide tungstates Ln2(WO4)3 (Ln = La, Sm, Eu, Gd) and the type of charge carriers is determined. The studied compounds have a salt-like isle structure with isolated tetrahedrons, which crystallise in the Еu2(WO4)3 structural type of the so-called 'defective scheelite' in which 1/3 of Ln sites are vacant, Ln2/3[VLn]1/3WO4. Predominant ionic conductivity in Ln2(WO4)3 (Ln = La, Sm, Eu, Gd) was established both by the EMF method and from independence of conductivity versus oxygen partial pressure, although Eu2(WO4)3 reveals a small contribution of the electronic n-type component. A minor contribution (1-5%) of the anion [WO4]2 − transport was detected by the Tubandt method, which along with the results of the EMF technique proves the predominant oxygen conductivity.