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An explanation for the origin of hemihedrism in wulfenite: the single-crystal structures of I 4 1 /a and I tungstenian wulfenites

2000; Cambridge University Press; Volume: 64; Issue: 6 Linguagem: Inglês

10.1180/002646100550056

1471-8022

David E. Hibbs, C. M. Jury, Peter Leverett, I. R. Plimer, Peter A. Williams,

Iron-based superconductors research

Abstract The single-crystal X-ray structure of tungstenian wulfenite- I 4 1 / a containing 10 mol.% WO 3 from the San Francisco mine, Sonora, Mexico, space group I 4 1 / a , a = 5.436(2), c = 12.068(8)Å and Z = 4, has been refined to R = 0.052. The Mo and W are disordered over special position 4 a (0,0,0) in the lattice. Tungstenian wulfenite- I 4̄ (‘chillagite’) from the Christmas Gift mine, Chillagoe, Queensland, Australia (Museum of Victoria specimen M16934), crystallizes in the closely related tetragonal space group I 4̄, with a = 5.441(1), c = 12.068(6) Å and Z = 4. The structure was refined to R = 0.038. Refined site occupancy factors show that Mo and W are not distributed equally over the two crystallographically independent Mo/W positions, being 0.136(2) for Mo and 0.114(2) for W in special position 2 a (0,0,0) and 0.184(2) for Mo and 0.066(2) for W in special position 2 c (0,Ý,Ü). These give a composition corresponding to wulfenite 64 stolzite 36 , in agreement with analytical data. The Mo/W distributions in the unit cell provide one explanation for the origin of hemihedrism in the wulfenite-stolzite series.