The aim of this work is the preparation of nitrogen-doped single crystals of cation-stabilized zirconia. Thin plates of these crystals were nitrided in a graphite heated resistance furnace with nitrogen as reaction gas. Several dwell times and reaction temperatures were tested and their effect on the amount of incorporated nitrogen is investigated. During nitridation at high temperatures a rock salt-type 'ZrN' layer grows on the surface, leading to the destruction of the crystal. In contrast to the fluorite-type bulk material, which can be described as a fast anion conductor, the surface layer shows electronic conductivity. For possible applications of the bulk material (solid electrolyte) the formation of the surface layer must be avoided. Therefore, the interface between surface epilayer and bulk material was investigated in detail by electron microscopy methods.
The structural evolution of a scandia/nitrogen co-doped zirconia sample, Sc0.148Zr0.852O1.72N0.14, was investigated by neutron powder diffraction up to 1700 °C. At ambient temperature it has an anion-deficient fluorite related β′-type structure with ordered anion vacancies (space group R-3, a = 9.5611 Å, c = 17.5020 Å). With increasing temperature a gradual transformation into a cubic fluorite-type phase (Fm3m) with randomly distributed vacancies takes place which is accompanied by an enrichment of Sc in the rhombohedral phase and completed at ∼1050°C. At higher temperatures probability densities and single particle potentials of the anions were determined. The incorporation of nitrogen into the scandia-zirconia material significantly increased the activation energy for anion migration to values above 1 eV. The anions migrate predominantly along the <100>-directions to neighbouring sites.
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