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

Z. Naturforsch. 54 b, 1277-1282 (1999); received May 27, 1999 Intermetallic Compounds, Crystal Structure, Close Packed Layers The new compounds GdReaAlio and TbRe.Alio 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 TbReiAlio from single-crystal X-ray data: Cmcm, a = 932.2(1),/?= 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 Tbo.948(5 >Re2Alio or Tbo.936(3 )Re:Alio.o64(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 4ReAl3; the other is planar and less densely packed. It has the mesh content 2TbAl4. The same kinds of atomic layers have been found in the structures of YbFe2 Alio and LuRe2 Alio. Thus, the three structure types may be considered as stacking variants of each other. The tetragonal CaC^Alio (ordered ThMni2 ) type structure also belongs to this structural family, although the CaAl4 layers somewhat differ from the layers TbAl4, YbAl4, and LuA14.