Antiferromagnetic and Crystal Structures of Alpha-Oxygen

X-ray diffractometer data from polycrystalline samples of alpha-oxygen frozen from the liquid are accounted for by a monoclinic structure: space group C2/m, b axis unique, a = 5.403±0.005, b = 3.429±0.003, c = 5.086±0.005 Å; β = 132.53±0.04°; volume = 69.44 Å3; calculated density = 1.530 g/cm3. The cell contains two molecules centered at the lattice points 000 and ½½0, which are symmetry centers. The atoms are at positions x, 0, z; x̄, 0, z̄; ½+x, ½, z; ½—x, ½, z̄, with x = 0.089±0.01, z=0.153±0.015. The nearest center-to-center distances between molecules is 3.20 Å and the 0–0 bonds are found to be perpendicular to the ab plane within an experimental accuracy of a few degrees. The published neutron diffraction data, interpreted on the basis of the structure, imply that the antiferromagnetic structure consists of antiparallel moments at 000 and ½½0.

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