Electron-beam induced in-situ transformations in SrFeO3−δ single crystals

Single crystals of SrFeO_3−δ iron(IV) oxides (δ?0.05) have been investigated by selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The crystals are characterized by a coherent intergrowth of multiple twinned tetragonal and cubic domains. According to Mössbauer spectroscopy and XRD, the cubic domains are the main component, particularly for SrFeO_3.00(2). The domain structure transforms significantly when performing HRTEM at room temperature. In a first and very rapid step of transformation the amount of the tetragonal domains increases dramatically. In a subsequent step the sizes of the tetragonal domains are changed via cubic intermediates. All in-situ transformations can be suppressed at low temperature where the typical SAED patterns of the cubic SrFeO₃ are observed. It is concluded that low temperature experiments are useful for an unambiguous characterization of the crystal structure and microstructure of high-valent transition metal oxides.