The Zr0.5−0.5xY0.5+0.25xNb0.25xO1.75 solid solution possesses an anion-deficient fluorite

structure across the entire 0 ≤ x ≤ 1 range. The relationship between the disorder

within the crystalline lattice and the preferred anion diffusion mechanism was

studied as a function of x, using impedance spectroscopy measurements of the

ionic conductivity (σ), powder neutron diffraction studies, including analysis of the

'total' scattering to probe the nature of the short-range correlations between ions

using reverse Monte Carlo modelling, and molecular dynamics simulations using

potentials derived with a strong ab initio basis. The highest total ionic conductivity

(σ = 2.66 x 10−2S/cm at 1473K) was measured for the Zr2Y2O7 (x = 0) end member,

with a decrease in σ with increasing x, whilst the neutron diffraction studies

showed an increase in lattice disorder with x. This apparent contradiction can be understood by considering the local structural distortions around the various cation

species, as determined from the reverse Monte Carlo modelling and molecular

dynamics simulations. The addition of Nb5+ and its stronger Coulomb interaction

generates a more disordered local structure and enhances the mobility of some

anions. However, the influence of these pentavalent cations was outweighed by the

effect of the additional Y3+ cations introduced as x increases, which effectively trap

many anions and reduce the overall concentration of the mobile O2− species.

Local Structure and Ionic Conductivity in the Zr2Y2O7–Y3NbO7 System.

S.T.Norberg, I.Ahmed, S.Hull, D.Marrocchelli, P.A.Madden: Journal of Physics -

Condensed Matter, 2009, 21[21], 215401