Oxygen ionic conductivity through zirconia was essential to the performance of solid oxide fuel cells, thermal barrier coatings, and zirconium alloys for nuclear fuel cladding. Since sulfur (S) atoms can replace oxygen atoms at ZrO2 surface or even induce formation of homogeneous zirconium oxysulfide structure at high S partial pressure, a study was made of defect migration and formation in both cubic zirconia (c-ZrO2) and ZrOS under different electron and element chemical potentials using density functional theory. The calculations showed that S addition to zirconia, either by doping or through gas diffusion, increases both the formation energy and migration barrier of doubly positively charged oxygen vacancies. Since the charged oxygen vacancies play a vital role in the ionic and thermal conductivities, the results suggested that high S partial pressures were expected to change the mechanisms of ionic and thermal conductivities of ZrO2-based materials.

Formation and Migration of Oxygen and Zirconium Vacancies in Cubic Zirconia and Zirconium Oxysulfide. O.I.Malyi, P.Wu, V.V.Kulish, K.Bai, Z.Chen: Solid State Ionics, 2012, 212, 117–22