Samples of CaTi1-xFexO3, where x was between 0.05 and 0.38, were synthesized at 900 to 1320C under controlled conditions of O fugacity. After drop quenching, the samples were characterized by means of X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy. Electrical conductivity measurements were performed as a function of temperature, O fugacity and sample composition. The X-ray diffraction data revealed no long-range ordering of O vacancies, and this was confirmed by transmission electron microscopy. Mössbauer spectroscopy showed that Fe occurred in octahedral, tetrahedral and penta-coordinated sites. An analysis of area ratios indicated that a small number of Ti atoms must be located on non-octahedral sites; where the relative proportion of Ti on these sites decreased with increasing concentration of O vacancies. The results were interpreted in terms of a model for the short-range ordering of O vacancies, in which clusters formed chains of increasing length. The structure was dominated by O vacancy monomers at low Fe concentrations, and the average number of vacancies per chain increased with increasing Fe concentration. The results were consistent with conductivity results, which revealed a high ionic conductivity at moderately low Fe concentrations.

Short-Range Ordering of Oxygen Vacancies in Ca(Fe,Ti)O3 Perovskites. C.A.McCammon, A.I.Becerro, F.Langenhorst, R.J.Angel, S.Marion, F.Seifert: Journal of Physics - Condensed Matter, 2000, 12[13], 2969-84