THE CRYSTAL-STRUCTURE OF A NEW TERNARY GERMANIDE, HO26PD4(PD,GE)(19-X)

The crystal structure of the compound Ho26Pd4(Pd, Ge)(19-x) was determ ined by the single-crystal method (DARTCH-1 automatic diffractometer, Mo K alpha radiation). Ho26Pd4(Pd, Ge)(19-x) is a substitutional varia nt of the Er26Ge23-x structure type: space group P4/nmm, a=14.523(6) A ngstrom, c=10.318(2) Angstrom, V=2176(2) Angstrom(3), Z=2, R(F)=0.0428 for 841 unique reflections. The coordination numbers of the holmium a toms are 14-17. For the germanium atoms tetragonal antiprisms and trig onal prisms are typical as coordination polyhedra. Those for the palla dium atoms are trigonal prisms and cubes. All coordination polyhedra h ave additional atoms. The structure of Ho26Pd4(Pd, Ge)(19-x) can be in terpreted as being built up of three kinds of fragment formed by rare earth atoms: (a) a stacking of tetragonal antiprisms and cubes; (b) a column of cubes; (c) a chain of trigonal prisms and tetragonal pyramid s. The relationships between the Ho26Pd4(Pd, Ge)(19-x) structure and t he Er26Ge23-x and Ce26Li5Ge22+x structure types are discussed.