Structure-modulated ionic transport behavior in zirconia–dysprosia mixed oxides

Abstract

In the present study, we report a systematic study on Zr1−xDyxO2−x/2 system exploring the effect of structure on ion-transport. All the compositions were synthesized by combustion route followed by high-temperature sintering and thoroughly characterized by X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and AC impedance studies. These studies revealed a phase relation wherein Zr0.9Dy0.1O1.95 exhibited coexistence of a monoclinic and cubic phase. The Dy3+ content greater than 10 mol% led to complete stabilization of cubic zirconia solid solutions. The structural evolution has also been monitored with Raman spectroscopy wherein very weak pyrochlore-type ordering in compositions with x ≥ 0.4 could be observed even when XRD showed a fluorite-type structure. The effect of structure-induced conductivity control was revealed by AC impedance analysis which bestowed a high ionic conductivity, 0.0048 Scm−1 at 700 K, on the nominal composition Zr0.8Dy0.2O1.90. This has been attributed to a very high disorder prevailing in this system due to the substitution of Zr4+ by Dy3+. It was revealed that the ionic conductivity behavior was driven by high pre-exponential factor which led to substantially high ionic conductivity for Zr0.8Dy0.2O1.90 despite almost equal activation energies observed for all the nominal compositions studied. Such high ionic conductivity for a zirconia-based system makes it a potential candidate for electrolyte for intermediate-temperature solid oxide fuel cell, as they are inherently stabler than ceria-based electrolytes.