S. Mahne et B. Harbrecht, AL69TA39 - A NEW VARIANT OF A FACE-CENTERED-CUBIC GIANT-CELL STRUCTURE, Journal of alloys and compounds, 203(1-2), 1994, pp. 271-279
The structure of Al69Ta39, cF432, a = 1915.3(10) pm, F43mBAR, Z = 4, 3
8 variables, was determined from 523 X-ray intensities of a single cry
stal with I > 3sigma(I) and refined to wR(1) = 0.050. Al69Ta39 represe
nts a new structure type composed of four compositionally and three to
pologically distinct metal atom clusters as present in alpha-Mn-, gamm
a-brass- and Cd45Sm11-type structures. The compositions of the cluster
s range from Al10Ta16 to Al23Ta. Deviations from the crystallographic
composition A172Ta39 are due to 50% occupation of one Al site. Eleven
out of 17 primary coordination polyhedra are of the Frank-Kasper type.
The remaining polyhedra can also be considered as being exclusively t
erminated by triangulated faces. They are either of b.c.c. type or the
y combine features of both Frank-Kasper and b.c.c. coordinations.