Tyrrellite, Cu(Co0.68Ni0.32)2Se4, isostructural with spinel.
Tyrrellite, a naturally occurring Co-Ni-Cu selenide, has been studied by single-crystal X-ray diffraction. It possesses the normal spinel-type structure, with Cu occupying the tetrahedral site and (Co+Ni) the octahedral site. The average Cu-Se distance of 2.3688 (2) A is close to that of 2.3703 (8) A in CuCr(2)Se(4), whereas the average (Co+Ni)-Se distance of 2.3840 (1) A appears to be slightly shorter than most octahedral Co-Se or Ni-Se distances ( approximately 2.40-2.50 A) in other selenides. The refined structure provides a basis for a redefinition of the ideal chemical formula of tyrrellite, which should be Cu(Co,Ni)(2)Se(4), rather than the previously suggested (Cu,Co,Ni)(3)Se(4).
Department of Geosciences, University of Arizona, 1040 East 4th Street, Tucson, AZ 85721-0077, USA. hyang@u.arizona.edu
Hexiong
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Yang
David K
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Hubler
Barbara
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Lavina
Robert T
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Downs
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Costin