It was noted that the conductivities of M2(WO4)3 solid electrolytes, where M was a rare earth, In or Al, ranged from 3.2 x 10-6 to 6.5 x 10-5S/cm; with corresponding activation energies of 44.1 to 91.0kJ/mol. These parameters could be improved, as in the case of Sc2(WO4)3, by the formation of mixed cationic tungstates with dissolved In, Lu, Dy or Gd. These larger cations acted so as to expand the host lattice and facilitate migration of the Sc3+ or Al3+ cations. Maximum enhanced conductivities of about 5 times (Sc3+ conductors) or 6 times (Al3+ conductors) were observed. The trivalent cations were quantitatively and qualitatively identified as being the mobile charge-carrying species, with a cationic transference number greater than 0.99. The Sc cations were found to be the main charge-carrying species in (Sc,M)2(WO4)3, where M was In, Dy or Gd. In (Sc,Lu)2(WO4)3 and (Al,Sc)2(WO4)3, the nature of the predominant charge carrier depended upon the composition.

Trivalent Cation Conduction in the Sc2(WO4)3-Type Structure. G.Adachi, J.Kohler, N.Imanaka: Electrochemistry, 1999, 67[7], 744-51