Oxygen vacancies disordering and oxy-ion diffusion mechanism in doped ceria electrolytes under IT-SOFC operating conditions

In the present attempt, order-to-disorder transition of oxygen vacancies and their correlation with ion transport mechanism in moderately (at.15%) and heavily (at. 30%) doped (Gd and Sm) ceria systems are explored by using a high-temperature X-ray diffraction (HT-XRD) and Raman and dielectrics spectroscopy techniques. Oxygen vacancies disordering is integrated with polarization phenomenon. The density of disordered oxygen vacancies and conducting ions is revealed by the imaginary part of electric modulus (M). Relaxations of conducting ions are confirmed by M as a function of frequency at various temperatures, and peak height M curve is used to quantify the density of disorder states. HT-XRD study exhibits detectable mismatch in lattice parameter during expansion and contraction at particular temperature. The mismatch parameter is correlated to kinetic process induced in the samples caused by long-range disordering of oxygen vacancies. HT-Raman spectra confirm temperature-dependent disordering of oxygen vacancies. The energy of disordering of oxygen vacancies at grain and grain boundaries region is calculated from the slope of the log (f(max)) versus 1000/T plots, where f(max) is the frequency associated with M(max). Disordering energy at the grain boundary is more than grain in almost all systems. The temperature correspond to the order-disorder transition of oxygen vacancies is closely associated with oxy-ion conductivity. Arrhenius plot of conductivity depicts the kink in the slope of the conductivity curves for all ceria systems for the temperature ranges from 400 to 500 degrees C. The activation energy of conductivity in the temperature region of ordered oxygen vacancies is more than disordered oxygen vacancies. Conductivity maxima are associated with the density of disordered oxygen vacancies.

Automated summary

The present study explores the order-to-disorder transition of oxygen vacancies in doped ceria systems and their correlation with ion transport mechanism using various techniques. The energy of disordering of oxygen vacancies is higher at grain boundaries compared to grains, and the temperature corresponding to the transition of oxygen vacancies is closely related to oxy-ion conductivity. Conductivity maxima are associated with the density of disordered oxygen vacancies.