Ternary stannides RE 2Au5Sn2 (RE = Gd-Er) – i3 superstructures of the Fe2P type

Abstract

Abstract The stannides RE 2Au5Sn2 (RE = Gd-Er) were synthesized by arc-melting of the elements and subsequent annealing in tantalum crucibles in sealed evacuated silica tubes. The samples were characterized by powder X-ray diffraction and two structures were refined on the basis of single-crystal X-ray diffractometer data: ordered Au7Ga2 variant, P 6 ¯ 2 m , $P\bar 62m,$ a = 820.14(4), c = 942.72(5) pm, wR2 = 0.0798, 789 F 2 values, 34 variables for Tb2Au4.70Sn2.30 and a = 816.1(1), c = 941.3(2) pm, wR2 = 0.0600, 723 F 2 values, 35 variables for Er2Au5.03Sn1.91. All stannides exhibit small homogeneity ranges resulting from Au/Sn mixing and/or defects within the tin substructure. The RE 2Au5Sn2 structures derive from the aristotype ZrNiAl (ordered version of Fe2P) by a group-subgroup relation (isomorphic transition of index 3). The crystal chemical details are discussed in comparison with the ZrNiAl type stannide CeRhSn which crystallizes with the subcell structure.