Abstract
Mixed holmium cobaltite-chromite HoCo0.5Cr0.5O3 with orthorhombic perovskite structure (structure type GdFeO3, space group Pbnm) was obtained by solid state reaction of corresponding oxides in air at 1373 K. Room- and high-temperature structural parameters were derived from high-resolution X-ray synchrotron powder diffraction data collected in situ in the temperature range of 300–1140 K. Analysis of the results obtained revealed anomalous thermal expansion of HoCo0.5Cr0.5O3, which is reflected in a sigmoidal temperature dependence of the unit cell parameters and in abnormal increase of the thermal expansion coefficients with a broad maxima near 900 K. Pronounced anomalies are also observed for interatomic distances and angles within Co/CrO6 octahedra, tilt angles of octahedra and atomic displacement parameters. The observed anomalies are associated with the changes of spin state of Co3+ ions and insulator-metal transition occurring in HoCo0.5Cr0.5O3.
Highlights
Rare earth (R) cobaltites RCoO3 and chromites RCrO3 with perovskite structure due to their high electrical conductivity, specific magnetic properties, as well as significant electrochemical and catalytic activity are considered as prospective electrode and interconnect materials for solid oxide fuel cells (SOFC) [1,2,3], thermoelectric and magnetocaloric materials [4,5,6], catalysts and humidity and gas sensors [7,8,9]
The obtained values of unit cell dimensions are in excellent agreement with the corresponding data for the parent HoCoO3 and HoCrO3 compounds (Fig. 1, inset 1), proving an apparent formation of continuous solid solution HoCo1–xCrxO3 with perovskite structure, to the related RCoO3–RCrO3 systems with La, Pr, Nd, Sm, Eu, Gd, Dy, Er and Y [18, 19, 28–33]
HoCo0.5Cr0.5O3 clearly illustrates an increasing population of the exited spin states of Co3+ ions with the Conclusions Crystal structure parameters of the mixed holmium cobaltite-chromite HoCo0.5Cr0.5O3 synthesized by solid state reaction in air at 1373 K have been studied in the temperature range of 300–1140 K by using highresolution X-ray synchrotron powder diffraction technique
Summary
Rare earth (R) cobaltites RCoO3 and chromites RCrO3 with perovskite structure due to their high electrical conductivity, specific magnetic properties, as well as significant electrochemical and catalytic activity are considered as prospective electrode and interconnect materials for solid oxide fuel cells (SOFC) [1,2,3], thermoelectric and magnetocaloric materials [4,5,6], catalysts and humidity and gas sensors [7,8,9]. RCoO3-based materials are of particular interest, due to dependency of their transport, magnetic and other properties on spin state of Co3+ ions, which can change with increasing of the temperature from low spin (LS, t26geg0, S = 0), to intermediate (IS, t25geg, S = 1) and high spin (HS, t24geg, S = 2) configurations ([14,15,16] and references ). These transitions in rare earth cobaltites RCoO3 are strongly affected by the chemical. For HoCoO3 no structural phase transitions are reported in a broad temperature range between 1.5 and 1098 K, pronounced anomalies are observed both in low- and
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