CrxRe1−xO2 oxides with different rutile-like structures: changes in the electronic configuration and resulting physical properties

Mixed chromium–rhenium oxides, CrxRe1−xO2 with 0.31⩽x⩽0.66, have been synthesized for the first time by high-pressure high-temperature synthesis and in evacuated quartz tubes. The crystal structures of the compounds have been determined by single crystal and powder X-ray diffraction. Depending on synthesis conditions (pressure and temperature) these phases crystallize either in a tetragonal structure (P42/mnm) with statistical distribution of metal ions on one site (rutile-type), with cation ordering along c-axis (trirutile-type), or in a monoclinic rutile-like structure (C2/m) with ordering of Cr- and Re-cations and metallic Re–Re bonds. The “a” parameter of the tetragonal unit cell increases with increasing Re content whereas the “c” parameter decreases, indicating a strengthening of the Re–Re bond. The thermal stability of tetragonal CrxRe1−xO2 in Ar-atmosphere depends on the Re-content, decomposition is observed at 1241 K for x=0.34, but already at 966 K for x=0.5. The thermal expansion of CrxRe1−xO2 is anisotropic with a larger expansion coefficient in the “c” direction. Tetragonal CrxRe1−xO2 with 0.31⩽x<0.54 order antiferromagnetically at low temperatures with TN depending on the Cr-content x.