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

Single crystals of SrFeO3−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 SrFeO3.00(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.