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

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.

Anomalous High Temperature Structural Behavior of Potential Multifunctional Material SmCo0.5Cr0.5O3

“…Similar temperature behavior of the above mentioned structural parameters was earlier reported for the isostructural PrCo 0.5 Cr 0.5 O 3 and HoCo 0.5 Cr 0.5 O 3 materials , . At that the average bond lengths < M –O> in SmCo 0.5 Cr 0.5 O 3 and PrCo 0.5 Cr 0.5 O 3 structures increases from 1.955 Å at 298 K to 1.99 Å at 1173 K being practically equal in whole temperature range investigated.…”

“…Examination of the obtained structural data allow to detect anomalous behavior of SmCo 0.5 Cr 0.5 O 3 crystal lattice, which is reflected in a sigmoidal temperature dependence of the unit cell dimensions (Figure ) and in sufficient increase of the thermal expansion coefficients (TEC's) with a broad maxima near 860 K (Figure ). Similar abnormal lattice parameters behavior was previously observed in the related mixed cobaltites‐chromites LaCo 1– x Cr x O 3 and R Co 0.5 Cr 0.5 O 3 ( R = Pr, Eu, Gd, Dy, Ho, and Er) …”

“…Similar abnormal lattice parameters behavior was previously observed in the related mixed cobaltiteschromites LaCo 1-x Cr x O 3 [8] and RCo 0.5 Cr 0.5 O 3 (R = Pr, Eu, Gd, Dy, Ho, and Er). [13][14][15][16] The linear expansion coefficients in b and c directions show nearly isotropic thermal behavior in the whole temperature range investigated, whereas thermal expansion in a direction is much more pronounced (Figure 3).…”

“…Similar temperature behavior of the above mentioned structural parameters was earlier reported for the isostructural PrCo 0.5 Cr 0.5 O 3 and HoCo 0.5 Cr 0.5 O 3 materials. [15,16] At that the average bond lengths ϽM-OϾ in SmCo 0.5 Cr 0. In references [9,10] it was shown that increasing structural deformation in the mixed cobaltite-chromites series NdCo 1-x Cr x O 3 and GdCo 1-x Cr x O 3 shifts the onset of spin transition of Co 3+ ions and insulator-metal transition to the highest temperatures.…”

Physical properties of Nano Crystalline Ceramic HoBaCrO

“…Perovskite rare-earth chromites with the general formula RCrO 3 comprise an important class of multiferoic materials [1][2][3][4] that exhibit an astonishing variety of physical properties including electric, dielectric, magnetic, magneto-caloric, optic properties and so on. As a result, in the past several years, they have been fully investigated due to the promising potentials of applications such as insultor-metal transition [5], fuel cells (SOFC) [6], magnetocaloric materials [7], oxygen sensors [8], dielectrics [9], optic-magneto devices [10]..... Several factors like the ionic size of the R 3+ rare earth, the atomic valency of Cr-ions [11], Jahn Teller distortion [12] and the exchange between the d-orbitals of the B transition metal cation and the 2p-orbitals of oxygen anions [13][14] profoundly influence the electric, magnetic and other properties of these materials. Furthermore, these properties and the spin state of Cr ions can be controlled by a partial substitution either in R or/and Cr cation sites [13,15,16] which introduces a remarkable lattice distortion leading to various defects in the structure [17,18].…”