Electrolytes based on pyrochlores such as Ln2M2O7 (M = Ti, Zr, Hf) have attracted attention due to their relative stability combined with high ionic conductivity at intermediate temperatures. There is an intimate relationship between fluorite and pyrochlore structures, the latter being essentially an oxygen deficient ordered form of the former. A total neutron scattering study of the pyrochlore-fluorite phase boundary in the system Yb2-xLa2xZr2O7 is proposed. A maximum of conductivity occurs in these types of systems at the phase boundary, which is correlated with a critical ratio of the radii of the A and B cations. The onset of cation and anion disorder will be examined as well as oxide ion vacancy distribution, through Reverse Monte Carlo analysis of the total neutron scattering data in combination with total X-ray scattering data, with a view to explaining the conductivity maximum.