Ternary phases in the Yb-Zn-Al system with La3Al11- and Yb8Cu17Al49-type structures

Several compounds with La3Al11- and Yb8Cu17Al49-type structures were synthesized in the ternary Yb-Zn-Al system and their crystal structure and existence range were determined by both single-crystal and powder methods. For two of them, crystallizing with the La3Al11-type, orthorhombic, Immm, o/28, refinement was made by single-crystal data: Yb3Zn6.16Al4.84, a = 428.95(4) pm, b = 975.5(1) pm, c = 1257.3(2) pm, wR2 = 0.052; Yb3Zn4.84Al6.16, a = 427.03(5) pm, b = 988.6(1) pm, c = 1249.5(2) pm, wR2 = 0.104. Though zinc and aluminium share the same sites, some preferential occupation is recognizable. This phase forms between 35 and 50 at% Al. On the Zn-rich side, starting from binary Yb3Zn11, a replacement of ∼3 at% Al for Zn is reached, then a heterogeneity range appears. Two other phases, crystallizing with the Yb8Cu17Al49-type, tetragonal, I4/mmm, tI74, were determined by single-crystal methods: Yb8Zn48.5Al17.5, a = 874.6(2) pm, c = 1615.8(3) pm, wR2 = 0.055; Yb8Zn41.4Al24.6, a = 869.5(3) pm, c = 1637.1(7) pm, wR2 = 0.104. The structure of these latter compounds can be related to the Th6Mn23 type. A common building unit is found and several coordination polyhedra show similar features. Two atomic sites with zinc only and four with Zn/Al mixtures are filled.