Phase relations and ionic transport behaviour in new mixed oxides of ceria–zirconia–gadolinia

The present study investigates structure and the phase relations observed in complex oxide systems obtained by substituting Gd2O3 in the mixed oxide (Ce0.8Zr0.2)O2. The X-ray diffraction studies performed on this system revealed two single-phasic phase-fields; fluorite-type (F-type) and C-type. The transformation from F-type to C-type structure was observed at 60 mol% Gd3+ substitution. The Raman spectroscopic studies, however, reveal further fine structural insights wherein the F-type region was observed only up to 30 mol% of Gd3+ which was followed by the co-existence of C-type ordered region and F-type region. The single-phasic C-type phase-field was observed only beyond 80 mol% Gd3+-substitution. The AC impedance analysis revealed minimum in the activation energy and maximum in ionic conductivity values as a function of Gd3+-content. An antagonistic interplay of activation energy and pre-exponential factor is explained as the major factor behind this behaviour. The determination of migration and association energies supported the trend observed in the ionic conductivity values as a function of Gd3+-content. The activation energies for hopping are in good agreement with migration activation energies thus establishing that the conduction mechanism involved hopping of oxygen ions. [Display omitted] •Presence of single-phasic F- and C-type phases was revealed by XRD studies.•Both, inter-anionic repulsions and ionic sizes governed the lattice parameters.•C-type micro domains in F-type region and vice versa observed by Raman spectra.•High conductivity of 30% Gd3+ doped sample agrees with low association energy.•Similar migration and hopping energies reveal the hopping mechanism for conduction.