Crystal Structure of the Transition-Metal Molybdates and Tungstates. II. Diamagnetic Sc2(WO4)3
1966; American Institute of Physics; Volume: 45; Issue: 8 Linguagem: Inglês
10.1063/1.1728021
ISSN1520-9032
Autores Tópico(s)Thermal Expansion and Ionic Conductivity
ResumoSc2(WO4)3, diamagnetic above 30°K, crystallizes in the orthorhombic system, Space Group Pnca, with lattice constants a=9.596±0.004, b=13.330±0.003, and c=9.512±0.004 Å at 298°K. The complete x-ray scattering pattern within a reciprocal lattice hemisphere of radius (sinθ)/λ=1.02 Å−1 was measured with PEXRAD. The crystal structure was solved by use of three-dimen sional Patterson and Fourier series and refined by the method of least squares, using 1731 independent structure factors. The final agreement factor R is 0.0622. Scandium atoms occupy slightly distorted octahedra, with average Sc–O=2.063 Å and Sc–O distances ranging from 2.026±0.015 to 2.124±0.010 Å. Two crystallographically independent W atoms are surrounded by somewhat distorted tetrahedra: the W–O distances vary from 1.695±0.009 to 1.829±0.016 Å, the average being 1.761 Å. The thermal vibrations are significantly anisotropic. Sc2(WO4)3 forms the structure type for 23 trivalent metal tungstates and molybdates, including the nine smaller rare-earth tungstates. The larger rare-earth tungstates, crystallizing in the Eu2(WO4)3 structure type, have 8 coordination about the rare-earth ion; the smaller have 6 coordination. A simple correlation is found between the variation in radius ratio due to the lanthanide contraction and the change in coordination.
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