Oxide ion conductivity in (Ba_<0.3>Sr_<0.2>La_<0.5>)(In_<1-x>M_x)O_<2.75> (M = Sc and Yb) systems

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We have investigated the crystal phase and oxide ion conductivity of (Ba0.3Sr0.2La0.5)(In1-xMx)O2.75 (M = Sc and Yb) systems as a function of dopant content and unit cell free volume. All peaks in the XRD diffraction patterns of these systems (x = 0.0 - 0.4) were found to be assignable to pure cubic symmetry. The lattice parameter of the Sc-doped system decreased monotonically with rising dopant content, while the Yb-doped one showed a monotonic increase. The oxide ion conductivity of these systems increased with a unit cell free volume. Above a volume of 2.43 × 10-2 nm3, the oxide ion conductivity decreased. The oxygen vacancy content of the systems was controlled to be constant over the whole compositional range, which suggests that the mobile oxygen content should also be constant over the whole range. Above a free volume of 2.43 × 10-2 nm3, a broad Raman mode emerged from 350 cm-1 to 400 cm-1, which might relate to the local distortion of oxygen octahedra. We conclude that the oxide ion mobility grows with increasing unit cell free volume up to a critical volume, and then the mobility is degraded by the local distortion of the oxygen octahedra.
2009-04-01