Distorted octahedra induced anisotropic strain and local disorder in delafossite CuCrO2

Abstract

Delafossites (ABO2) are of great interest since they exhibit interesting structural and magnetic transitions. Edge shared geometry of octahedra in delafossites gives rise to distortion in octahedra. These distortions can influence the structural and physical properties of these materials. In the present study, the temperature dependence of structural changes related to CrO6 octahedra in CuCrO2 (a member of the delafossite family) has been investigated. Rietveld analysis of room temperature XRD data indicates that anisotropic strain, along with preferred orientation, is present in the sample. At room temperature, the CrO6 octahedra were found distorted. Careful analysis of temperature-dependent (300–610K) synchrotron X-ray diffraction data indicates that the degree of distortion of octahedra decreases with increasing temperature. Bond length Cu–O shows negative thermal expansion, which was driven by the reduction in the distortion of octahedra with increasing temperature. The existence of distorted octahedra has been proposed to be the reason for breaking the local symmetry, which is anticipated to be responsible for the presence of experimentally observed forbidden modes in the Raman spectra. © 2021 Elsevier Masson SAS