Anomalous Thermal Expansion of HoCo0.5Cr0.5O3 Probed by X-ray Synchrotron Powder Diffraction

Vasyl Hreb; Leonid Vasylechko; Vitaliya Mykhalichko; Yurii Prots

doi:10.1186/s11671-017-2213-7

Anomalous Thermal Expansion of HoCo_0.5Cr_0.5O₃ Probed by X-ray Synchrotron Powder Diffraction

Nanoscale Res Lett. 2017 Dec;12(1):442. doi: 10.1186/s11671-017-2213-7. Epub 2017 Jul 5.

Authors

Vasyl Hreb¹, Leonid Vasylechko², Vitaliya Mykhalichko², Yurii Prots³

Affiliations

¹ Lviv Polytechnic National University, 12 Bandera Street, 79013, Lviv, Ukraine. wasiahreb@meta.ua.
² Lviv Polytechnic National University, 12 Bandera Street, 79013, Lviv, Ukraine.
³ Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187, Dresden, Germany.

Abstract

Mixed holmium cobaltite-chromite HoCo_0.5Cr_0.5O₃ 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 HoCo_0.5Cr_0.5O₃, 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 HoCo_0.5Cr_0.5O₃.

Keywords: Crystal structure; Mixed cobaltites-chromites; Perovskite; Thermal expansion.