The trivalent ionic conduction in the Sc-2(WO4)(3)-Gd-2(WO4)(3) solid
solution with the Sc-2(WO4)(3)-type structure was investigated. The so
lubility limit of Gd3+ in Sc-2(WO4)(3) is 60 mol% in the Sc site and t
he lattice size of the solid solution isotropically expands with incre
asing the Gd3+ content. The ionic conductivity of the system greatly i
ncreased with an increase of the Gd3+ substitution and the maximum val
ue of 6.2 x 10(-5) S cm(-1) at 600 degrees C was obtained for the comp
osition, Sc1.6Gd0.4(WO4)(3), which is three times higher than that of
pure Sc-2(WO4)(3). The electrolysis result explicitly indicates that t
he predominant mobile species in the solid solution with the Sc-2(WO4)
(3)-structure is trivalent Sc3+ ion and that Gd3+ ion in the electroly
te acts as a lattice forming ion to obtain a suitable lattice size for
the Sc3+ ion migration. (C) 1998 Elsevier Science B.V. All rights res
erved.