UCONIGE2, NONMAGNETIC SOLID-SOLUTION OF THE ANTIFERROMAGNETS UCO2GE2 AND UNI2GE2

The compounds UCo2Ge2 and UNi2Ge2 crystallize in the body-centered tet ragonal ThCr2Si2-type structure (space group I4/mmm) and order with th e AF-I antiferromagnetic structure [k=(0,0,1)]. Two polycrystalline sa mples of UCoNiGe2, an intermediate solid solution of these compounds, have been prepared under identical conditions and studied by x-ray and neutron diffraction. Both samples crystallize in the lower-symmetry p rimitive tetragonal CaBe2Ge2-type structure (space group P4/nmm). The cobalt/nickel distribution in the M = (Co,Ni) planes in both samples i s not random, with Co:Ni ratios of 36:64 in M2 planes, close to U plan es, and 64:36 in doubly dense and distant M1 planes. Absence of magnet ic order in UCoNiGe2 down to 10 K, is associated with its lower symmet ry.