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 (P4(2)/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 anti ferromagnetically at low temperatures with T-N depending on the Cr-content x. (C) 2009 Elsevier Inc. All rights reserved.