STRUCTURE OF Y3TANI6- A FILLED-UP SUBSTITUTION VARIANT OF THE BAHG11 TYPE(XAL26 )

The crystal structure of Y3TaNi6+xAl26 (refined composition Y3TaNi6.30 (7)Al-25.84(6)) was determined by single-crystal X-ray diffraction (la mbda(Mo K alpha) = 0.71073 Angstrom, mu = 17.827 mm(-1), F(000) = 700, T = 293 K, wR = 0.015 for 181 unique reflections). This new quaternar y aluminide crystallizes with a cubic structure, Pearson code cP49-12. 85, (221) Pm-3m-ji(2)gdba, a = 8.3600(1) Angstrom, V = 584.28(2) Angst rom(3), Z = 1, M(r) = 1510.25, D-x = 4.292 mg mm(-3). The structure of Y3TaNi6+xAl26 is filled-up substitution variant of the BaHg11 structu re type with one additional atom site, partly occupied (around 15%) by Ni atoms, located at the centre of a cube formed by Al atoms. Distinc t atom coordinates were refined for Ni and Al atoms on a site for whic h mixed occupation (approximately 50% Ni/50% Al) was found. The Ta ato ms centre regular Al atom cuboctahedra, and the Y atoms 20-vertex poly hedra, formed by Al and Ni atoms, similar to those observed in CeMn4Al 8 and YbFe2Al10.