Growth and characterization of large high quality bownmillerite CaFeO2.5 single crystals

The growth conditions of large and high quality single-crystals of CaFeO2.5 by the floating-zone technique in an image furnace are discussed. Structural characterization of the as grown single crystals have been carried out by neutron and X-ray diffraction as well as by HRTEM revealed the excellent quality in terms of composition homogeneity and crystalline quality. Magnetic measurements have been performed on oriented crystals by SQUID and neutron diffraction in the range of 5–700 K in order to clear up controversial discussions on possible magnetic phase transitions. The magnetic transitions reported elsewhere are discussed in terms of oxygen non-stoichiometries leading to multiphase CaFeO2.5±δ related to the crystal growth conditions.