|Speciale, 3. modul, 2008, id:253|
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The oxygen diffusion and electrical conductivity of the K2NiF4-type oxides (formel) are determined from Electrical Conductivity Relaxation experiments. The results are related to models of the defect chemistry determined from measurements of the oxygen non-stoichiometry, deltac as a function of temperature and PO2. Both the ionic diffusion coefficient of the oxide ions and the electrical conductivity increases significantly with increasing amounts of Sr and are strongly dependent on the PO2. For x = 1.1. The strong variations in the diffusion coefficient can not be well explained form the variations of the concentration of oxygen vacancies. The strong decrease of the diffusion coefficient with decreasing PO2 observed for x = 1.1 might be due to association or ordering of oxygen vacancies. Measurements of thermal and chemical expansions are made on the above-mentioned oxides as well as on (formel). The thermal expansions increase with increased Sr content but depends only little on the size of the A-site cation. The chemical expansions are hardly obervable down to PO2s down to (formel) due to small losses of oxygen and small chemical expansion coefficients. From thermogravimetry measurements it was established that the samples are slightly sub-stoichiometric with respect to oxygen and that the oxygen content is very stable at temperatures up to 1000 degrees C. and in PO2 down to (formelt). The higher the Sr content, the more easily does the sample lose oxygen and this might explain the larger thermal expansions of the Sr rich samples.