Ionic conductivity across the disorder–order phase transition in the NdO1.5–CeO2 system

Solid solutions of NdxCe1 − xO2 − δ (0.05 ≤ x ≤ 0.55) are prepared via solid-state reactions and the grain ionic conductivity is measured using a two-probe ac impedance spectroscopy technique. The lattice parameters increased linearly with Nd content for 0.05 ≤ x ≤ 0.45. Both XRD and neutron diffraction analyses indicate at x = 0.50 the highly defective fluorite stabilizes into a C-type rare earth oxide structure with an associated doubling of the unit cell. The conductivity of the compounds follows an Arrhenius-type behavior showing a maximum conductivity of 0.054(1) S cm− 1 for Nd0.15Ce0.85O1.925 at 700 °C with an associated activation energy of 0.726(5) eV. The activation energy increases significantly during the phase transition from 35% to 40% Nd due to the stabilization of oxygen vacancies. The pre-exponential factor increased as well, resulting in an effective gradual decrease of conductivity across the phase transition.

► The effect of disorder–order phase transition on ionic conductivity is investigated.
► Room temperature XRD and neutron diffraction indicate that the phase transition takes place at 50% Nd concentration.
► The phase transition is observed to happen at 40% Nd from conductivity data at higher temperatures.