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Abstract: Single crystals of LiCr(MoO4)2, Li3Cr(MoO4)3 and Li1.8Cr1.2(MoO4)3 were grown by a flux method during the phase study of the Li2MoO4–Cr2(MoO4)3 system at 1023K. LiCr(MoO4)2 and Li3Cr(MoO4)3 single phases were synthesized by solid-state reactions. Li3Cr(MoO4)3 adopts the same structure type as Li3In(MoO4)3 despite the difference in ionic radii of Cr3+ and In3+ for octahedral coordination. Li3Cr(MoO4)3 is paramagnetic down to 7K and shows a weak ferromagnetic component below this temperature. LiCr(MoO4)2 is isostructural with LiAl(MoO4)2 and orders antiferromagnetically below 20K. The magnetic structure of LiCr(MoO4)2 was determined from low-temperature neutron diffraction and is based on the propagation vektor . The ordered magnetic moments were refined to 2.3(1)μB per Cr-ion with an easy axis close to the [111¯] direction. A magnetic moment of 4.37(3)μB per Cr-ion was calculated from the Curie constant for the paramagnetic region. The crystal structures of the hitherto unknown Li1.8Cr1.2(MoO4)3 and LiCr(MoO4)2 are compared and reveal a high degree of similarity: In both structures MoO4-tetrahedra are isolated from each other and connected with CrO6 and LiO5 via corners. In both modifications there are Cr2O10 fragments of edge-sharing CrO6-octahedra. [Copyright &y& Elsevier]

Abstract: Mixed chromium–rhenium oxides, Cr x Re1− x O2 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 Cr x Re1− x O2 in Ar-atmosphere depends on the Re-content, decomposition is observed at 1241K for x=0.34, but already at 966K for x=0.5. The thermal expansion of Cr x Re1− x O2 is anisotropic with a larger expansion coefficient in the “c” direction. Tetragonal Cr x Re1− x O2 with 0.31⩽x<0.54 order antiferromagnetically at low temperatures with T N depending on the Cr-content x. [Copyright &y& Elsevier]

Abstract: Different polymorphs of MRe2O6 (M i) with rutile-like structures were prepared using high-pressure high-temperature synthesis. For syntheses temperatures higher than ∼1573K, tetragonal rutile-type structures (P42/mnm) with a statistical distribution of M- and Re-atoms on the metal position in the structure were observed for all three compounds, whereas rutile-like structures with orthorhombic or monoclinic symmetry, partially ordered M- and Re-ions on different sites and metallic Re–Re-bonds within Re2O10-pairs were found for CoRe2O6 and NiRe2O6 at a synthesis temperature of 1473K. According to the XPS measurements, a mixture of Re+4/Re+6 and M 2+/M 3+ is present in both structural modifications of CoRe2O6 and NiRe2O6. The low-temperature forms contain more Re+4 and M3+ than the high-temperature forms. Tetragonal and monoclinic modifications of NiRe2O6 order with a ferromagnetic component at ∼24K, whereas tetragonal and orthorhombic CoRe2O6 show two magnetic transitions: below ∼17.5 and 27K for the tetragonal and below 18 and 67K for the orthorhombic phase. Tetragonal FeRe2O6 is antiferromagnetic below 123K. [Copyright &y& Elsevier]

Abstact: A new phase in the system Sc–Re–O, ScRe2O6, was synthesized for the first time in sealed silica tubes and its crystal structure was solved by single crystal X-ray diffraction. ScRe2O6 (space group P21/a, a=5.6176(9)Å, b=4.7970(9)Å, c=7.5143(16)Å, β=97.49(2)°, Z=2) crystallizes in a new rutile-type structure, derived from three formula units by splitting the cation site in ratio 1:2. Re2O10 clusters can be considered as structural units, in which the rhenium ions form pairs by metallic bonds with a Re–Re distance of 2.523(3)Å. No phase transition was observed in the temperature range of 295–930K. The compound has a metallic character of conductivity in the temperature range of at least 4–950K and displays a ferromagnetic ordering above room temperature (“unconventional Re-magnetism”). [Copyright &y& Elsevier]