ELSEVIER Journal of Alloys and Compounds 216 (1994) 231-235 Journal of AND COM~O~)5 The crystal structure of a new ternary germanide, Hoz6Pd4(Pd, Ge)a9-x O.L. Sologub, Yu.M. Prots', P.S. Salamakha*, V.K. Pecharsky, O.I. Bodak Department of Inorganic Chemistry, L'viv State University, Lomonosov Str. 6, 290005 L'viv, Ukraine Received 22 April 1994 Abstract The crystal structure of the compound Ho26Pd4(Pd, Ge)lg-x was determined by the single-crystal method (DARTCH-1 automatic diffractometer, Mo Kot radiation). Ho26Pd4(Pd, Ge)ag-x is a substitutional variant of the Er26Ge2a-x structure type: space group P4/nmm, a= 14.523(6) ]k, c=10.318(2) /~, V=2176(2) ~a Z=2, RF=0.0428 for 841 unique reflections. The coordination numbers of the holmium atoms are 14-17. For the germanium atoms tetragonal antiprisms and trigonal prisms are typical as coordination polyhedra. Those for the palladium atoms are trigonal prisms and cubes. All coordination polyhedra have additional atoms. The structure of Ho26Pd4(Pd, Ge)w_x can be interpreted 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 pyramids. The relationships between the Ho26Pd4(Pd, Ge)w-x structure and the Er26Ge23-~ and Ce26LisGe2z+x structure types are discussed. Keywords- Germanides; Arc melting; Annealing 1. Introduction Investigations of the ternary system Ho-Pd-Ge showed that besides the phases known in the literature -- HoPd2Ge (YPd2Si type) [1], HoPdGe (CeCu2 type) [2], HoPdl_~Ge2 (CeNiSi2 type), HoPdo.6Gel.4 (AIB2 type), HoEPdGe6 (Ce2CuGe6 type), HoPdEGe2 (Ce- GaEA12 type) [3] and Ho3Pd4Ge4 (Gd3eu4Ge4 type) [4] there exists a compound HOE6Pd4(Pd, Ge)lg-x with a structure similar to ErE6Ge23_~ [5]. This paper presents the results of a structure determination of the new ternary HoE6Pd4(Pd, Ge)19-~ phase. 2. Experimental details A sample of HosoPdlsGe35 was prepared from high purity elements (Ho, 99.9 wt.%; Ge and Pd, 99.99 wt.%) by direct arc melting under an argon atmosphere, annealing at 870 K in evacuated quartz ampoules for 2 weeks and quenching in cold water. The weight loss *Corresponding author. during the synthesis of an ingot of mass 0.5 g was 0.1%. Prism-like single crystals of the ternary germanide with dimensions of 0.015 × 0,015 × 0.050 mm 3 were stud- ied preliminarily using the Laue, rotation and Weis- senberg methods (Mo Ka and Cu Ka radiation). A survey of diffraction data for the Ho26Pd4(Pd, Ge)a9_ x structure was carried out using a DARTCH- 1 automatic four-circle diffractometer with a graphite monochromator (1333 measured and 841 unique re- flections, Mo Ka radiation, 0--20 scanning, cut-off thresh- old I(hkl)> 4o(0 and absorption correction by the azi- muthal scan technique). The unit cell parameters were refined from the 20 values of 28 reflections (Mo Ka radiation, 16°<20<33°). Attempts to refine the dis- placement parameters of Pdl atoms (2c) in the ani- sotropic approximation failed, so the isotropic ap- proximation was used. The difference in the number of electrons of Pd and Ge atoms permitted us to distinguish easily their relative contributions to the diffraction pattern of Ho26Pd4(Pd, Ge)w_ x. The M1 and M2 sites are fully occupied statistically by Pd and Ge atoms. Only for one position, 2c, which is partially 0925-8388/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0925-8388(94)01276-N