NEW YTTERBIUM COMPOUNDS WITH THE BAAL4 TYPE OF STRUCTURE - CRYSTAL-CHEMISTRY AND MAGNETIC-PROPERTIES OF YB(CU,AG,AU,PD,PT)XGA4-X

Ternary samples with the composition Yb(Cu,Ag,Au,Pd,Pt)xGa4-x have been synthesized from the elements by high frequency melting followed by heat treatment at 600-degrees-C. The crystal structure of all compounds was investigated using X-ray single-crystal or powder techniques and belongs to the BaAl4 type of structure. The homogeneity regions of the Yb(Cu,Ag,Au,Pd,Pt)xGa4-x phases have been established from X-ray powder diffraction analyses and lie in the range x = 0.30-0.95 for Cu, 0.25-0.43 for Ag, 0.22-1.45 for Au, 0.23-0.65 for Pt and near x = 0.25 for Pd. The unit cell dimensions vs. composition reveal a significant deviation from Vegard's rule for Cu and Au and a slight deviation for Ag and Pt. A partially ordered occupation of the 4d and 4e sites in the BaAl4 structure type has been found depending on the M/Ga ratio in the homogeneity range. The weak temperature-dependent paramagnetism of these compounds is due to the non-magnetic ground state of ytterbium (Yb2+). However, for YbPt0.5Ga3.5 a rather intermediate valence behaviour (Yb2+ --> Yb3+) is encountered.