Trivalent Cation Conduction in the Sc2(WO4)3-Type Structure

The electrical conductivity of the M2(WO4)3(MRare EarthInAl)solid electrolyte series amounts to32 10 6-6510-5 1cm-l with corresponding activation energies of441-91O kJmoL These electrical properties canbe individually improvedas is exemplary shownforthe case of Sc2(WO4)3and Al2(WO4)3bythe formation of mixed cationic tungstates of the type(Sc1 M)2(WO4)3(MInLuDyGd)and(Al1-xScx)2(WO4)3solid solutionsrespectively The larger cations(-3s3and313)act to expand the host lattice for an easier migration of the Sc3and A13cationsrespectivelyMaximum enhanced conductivities of about5times (Sc3conductors)and6times(A13conductors)havebeenobservedThe trivalent cations(M)were quantitatively and qualitatively i(ientified as mobile charge carrying species with a cationic transference number of099 Scandium cations have been identified in(ScMx)2(WO4)3(MInDyGd)as main charge carrying species whereas in(Sc1Lu)2(WO4)3and(AlScx)2(WO4)3the predominant charge carrier changes in dependence on the compositionThe experimental procedure for the characterization of M2(WO4)3and(ScM)2(WO4)3as trivalent cation1c conducting solid electrolytes is also given Sc2(WO4)3Type StmctureRare EarthsIonic ConductivityTrivalent Cation 1 1ntroduction Recentlycompounds in the Sc2(WO4)3structure type(in general M2(WO4)3)have gained high interest conceming the fundamental question whether trivalent cations are able to migrate through a crystalline solid or notNumerous different M2(WO4)3 tungstatesdiffering in Mhave been synthesized and characterized by various electrochemical methods AsafinalresultthetrivalentcationsMaredefinitely identified to be the mobile charge carrying species1-7)