Structural Behavior in the EUCoO₃-EuFeO₃ System

The work deals with the study of the phase and structural behaviour of mixed europium cobaltites-ferrites formed in the EuCoO3-EuFeO3 pseudo-binary system. Formation of a continuous solid solution EuCo1-xFexO3 with orthorhombic perovskite structure (GdFeO3 type, space group Pbnm) has been revealed. Crystal structure parameters of the mixed europium cobaltites-ferrites have been established by the full profile Rietveld refinement. Based on the analysis of structural parameters, an influence of the cation substitution on the deformation of the orthorhombic perovskite structure in the EuCo1-xFexO3 series has been established

Anomalous Thermal Behaviour of Mixed Cobaltites-Ferrites and Cobaltites-Chromites

Series of the mixed cobaltites-ferrites RCo1−xFexO3 (x = 0.1–0.9) and cobaltites-chromites RCo0.5Cr0.5O3 (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er) with the orthorhombic perovskite structure (space group Pbnm) have been prepared from stoichiometric amounts of rare earth oxides, Co3O4, Fe2O3 and Cr2O3 by solid-state reaction in air at 1473–1573 K. In situ high-temperature X-ray synchrotron powder diffraction revealed anomalous lattice expansion of both series, which is reflected in a sigmoidal dependence of the unit cell dimensions and in abnormal anisotropic increase of the thermal expansion coefficients (TEC). Depending on the composition, several broad maxima in the temperature range of 500−1000 K are observed, which are evidently connected with the transitions of Co3+ cations to the higher spin states. The observed anomalies in the mixed cobaltites-ferrites and cobaltites-chromites are less pronounced compared with the corresponding “pure” cobaltites

Thermal Behaviour of PrCo_{1-x}Fe_xO₃ Probed by X-ray Synchrotron Powder Diffraction and Impedance Spectroscopy Measurements

Crystal structure and transport properties of the mixed praseodymium cobaltites-ferrites PrCo_{1-x}Fe_xO₃ have been studied in the temperature range of 298-1173 K by a combination of in situ X-ray synchrotron powder diffraction and temperature dependent impedance spectroscopy measurements. In situ high temperature powder diffraction examination of PrCo_{1-x}Fe_xO₃ series revealed considerable anomalies in the lattice expansion which are especially pronounced for the cobalt-rich specimens. These anomalies, which are reflected in a sigmoidal dependence of the unit cell dimensions and in the considerable increase of the thermal expansion coefficients, are obviously associated with transitions of Co^{3+} ions from low spin to the higher spin states and the coupled metal-insulator transitions, occurring in in rare earth cobaltites at the elevated temperatures. Indeed, the temperature-dependent impedance measurements clearly prove the change of conductivity type from dielectric to the metallic behaviour in the mixed cobaltite-ferrites PrCo_{1-x}Fe_xO₃ at the elevated temperatures

Sol-Gel-Prepared Nanoparticles of Mixed Praseodymium Cobaltites-Ferrites

Two series of nanocrystalline powders of PrCo1-xFexO3 (x = 0.1, 0.3, 0.5, 0.7 and 0.9) of high purity were obtained by sol-gel citrate method at 700 and 800 degrees C. The formation of continuous solid solution with an orthorhombic perovskite structure (sp. group Pbnm) was observed. A peculiarity of the PrCo(1-x)FexO(3) solid solution is the lattice parameter crossovers, which occurred at certain compositions and revealed in the pseudo-tetragonal or pseudocubic metric. An average crystallite size of the PrCo(1-x)FexO(3) samples estimated from the analysis of the angular dependence of the X-ray diffraction (XRD) line broadening varies between 30 and 155 nm, depending on the composition and synthesis temperature