Electronic state of trivalent ionic conductors with Sc2(WO4)3-type structure

The electronic state of M2(WO4)3 trivalent ion conductors (M=Al, Sc, Lu, Yb, Tm, Er, Y) was calculated by the discrete-variational Xα molecular orbital (DV-Xα MO) method. The bond overlap populations between the M3+ ion and the surrounding oxide ions and the net charge of M3+, W6+, and O2− ions were compared with the experimental ionic conductivity of M2(WO4)3 crystals. The variation of the activation energy of ionic conductivity agreed qualitatively with the change of the bond overlap population between the migrating trivalent ion and the surrounding oxide ions. This result suggests that the bonding state of the trivalent ions plays an important role in trivalent ion conduction in M2(WO4)3 crystals.