The Intermetallic Compounds GdRe₂Al₁₀ and TbRe₂Al₁₀, Crystallizing with a Stacking Variant of the YbFe₂Al₁₀ Type Structure

Abstract

The new compounds GdRe 2 Al 10 and TbRe 2 Al 10 were obtained in well-crystallized form by reaction of the elemental components with an excess of aluminum after dissolving the matrix in hydrochloric acid. They crystallize with a new structure type which has been determined for TbRe 2 Al 10 from single-crystal X-ray data: Cmcm, a = 932.2(1), b = 1030.4(1 ), c = 1803.2(3)pm, Z = 8, R = 0.031 for 1159 structure factors and 77 variable parameters. Of the two terbium sites, one does not have full occupancy with terbium, however, it may have mixed Tb/Al occupancy. The resulting compositions are Tb 0.948(5) Re 2 Al 10 or Tb 0.936(3) Re 2 Al 10.064(3) , respectively. The terbium atoms are coordinated by 4 Re and 16 Al atoms. The rhenium atoms are situated in distorted icosahedra formed by 2 Tb and 10 Al atoms. The nine different aluminum atoms have between 12 and 14 neighbors (1 or 2 Tb, 2 Re, and between 8 and 11 Al atoms). The structure may be viewed as consisting of two kinds of alternating layers. One of these is puckered, hexagonal close packed, with a mesh content of 4ReAl 3 ; the other is planar and less densely packed. It has the mesh content 2TbAl 4 . The same kinds of atomic layers have been found in the structures of YbFe 2 Al 10 and LuRe 2 Al 10 . Thus, the three structure types may be considered as stacking variants of each other. The tetragonal CaCr 2 Al 10 (ordered ThMn 12 ) type structure also belongs to this structural family, although the CaAl 4 layers somewhat differ from the layers TbAl 4 , YbAl 4 , and LuAl 4 .