DETERMINATION OF THE OXYGEN NON-STOICHIOMETRY OF SrFeO_(3-x)

摘要

The oxygen non-stoichiometry in SrFeO_(3-x) was determined by coulometric titration in the temperature range, 750 to 1040°C and in the pO_2 range, 10~(-18) to 0.5 atm. At temperatures below 850°C, a two-phase region was observed composed of a mixture of perovskite and an oxygen vacancy ordered phase (Brownmillerite). Equilibrium was very difficult to achieve in this region. Above 850°C, no phase separation was apparent and reproducible data for the non-stoichiometry, x, were obtained both on increasing and decreasing pO_2. A simple, non-interacting point defect model reproduces the data at 1040°C but at lower temperatures, defect interactions must be included to obtain satisfactory agreement. The non-stoichiometry data are compared with previous results including recently reported conductivity data. The comparison shows that the p to n transition observed in the conductivity isotherms occurs at SrFeO_(2.505) at 950°C and SrFeO_(2.508) at 900°C, respectively.