THE MU-PHASE OF CO6.3NB6.7

The rhombohedral structure of the mu-phase Co6.30Nb6.70, space group R (3) over bar m, Pearson symbol hR39, was refined from X-ray diffracti on data of an obverse-reverse twinned crystal. The Co atoms have disto rted icosahedral environments, the Nb atoms have coordination numbers 12, 14, 15 and 16, and configurations typical for Frank-Kasper phases. The structure is quantitatively analysed in terms of the dihedral ang les and ranges of the edge lengths of the distorted tetrahedra. It is shown that the derived mean values hardly differ from those calculated for other representatives of tetrahedrally close-packed structure typ es.