CONCENTRATION OF POINT DEFECTS IN OXIDES: Ni_(1-δ)O, Co_(1-δ)O, Fe_(1-δ)O, Mn_(1-δ)O, Cu_(2-δ)O AND TiO_(2-δ) SHORT SUMMARY AND DISCUSSION

摘要

The diagrams of the concentrations of defects, presented in previous sections, allow for an analysis of the concentrations of ionic defects and electronic defects and their changes depending on the oxygen pressure and the deviation from the stoichiometry. From the analysis of diagrams for the oxides: Ni_(1-δ)O, Co_(1-δ)O, Fe_(1-δ)O, Mn_(1-δ)O, having the same cubic structure of NaCl-type, it transpires that despite a small difference in the electronic configuration of metal ions, their oxides differ significantly by the range of oxygen pressures where the individual phases exist and by the structure and concentrations of point defects. In these oxides, the dominating defects are cation vacancies and electron holes. Each oxide has significantly different diagram of the concentrations of defects. The oxygen pressure where the oxides: NiO, CoO and FeO could have reached the stoichiometric composition is by a few orders of magnitude lower than the decomposition pressure. An exception is MnO which has the lowest decomposition pressure (10~(-27) - 10~(-15) atm in the temperature range of 1173 - 1773 K) and it reaches the stoichiometric composition near this pressure. On the other hand, the Cu_(2-δ)O oxide has a different crystallographic structure (cuprite-type (C3)). It shows a significant concentration of defects in the cation and oxygen sublattices and in the range of its existence the Cu_2O reaches the stoichiometric composition. Significantly different from the above oxides is the titanium oxide, TiO_(2-δ) (with rutile-type structure), which, before all, has a significant concentration ofoxygen defects, but also cation defects and which is an electronic semiconductor. The TiO_2 reaches the stoichiometric composition at pressures near 1 atm. On the other hand, the highest concentration of defects occurs at the lowest oxygen pressures, at the TiO_(2-δ)/Ti_(16)O_(31) phase boundary.