Abstract
At room temperature, the normal oxide spinels NiCrO and CuCrO are tetragonally distorted and crystallize in the space group due to cooperative Jahn-Teller ordering driven by the orbital degeneracy of tetrahedral Ni () and Cu (). Upon cooling, these compounds undergo magnetic ordering transitions; interactions are somewhat frustrated for NiCrO but not for CuCrO. We employ variable-temperature high-resolution synchrotron x-ray powder diffraction to establish that at the magnetic ordering temperatures there are further structural changes, which result in both compounds distorting to an orthorhombic structure consistent with the space group. NiCrO exhibits additional distortion, likely within the same space group, at a yet-lower transition temperature of K. The tetragonal to orthorhombic structural transition in these compounds appears to primarily involve changes in NiO and CuO tetrahedra.
6 More- Received 25 June 2012
DOI:https://doi.org/10.1103/PhysRevB.86.054406
©2012 American Physical Society