The Crystal Data of Ternary Rare Earth Borides, RCo2B2

Compounds with the composition of RCo2B2 (R=La, Nd, Sm, Gd, Tb, Dy, and Y) were prepared by arcmelting methods. Their crystal structure was investigated by means of X-ray diffraction. These ternary rare earth borides crystallize in the tetragonal lattice. The lattice parameters are a=3.616±0.003 Å and c=10.215±0.005 Å for LaCo2B2 and a=3.561±0.002 Å and c=9.358±0.005 Å for YCo2B2. The good agreement between the X-ray diffraction intensities observed and those calculated shows that the ternary borides, LaCo2B2 and YCo2-B2, crystallize in the ThCr2Si2-type structure. The crystallographic data obtained for LaCo2B2 and YCo2B2 are as follows: space group 14/mmm(D4h17); 2R in 2(a), 4Co in 4(d), and 4B in 4(e) with z∼3⁄8. The boron atoms in this structure are situated at the center of a trigonal prism formed by four rare earth atoms and two cobalt atoms. We also found the RCo2B2 compounds to be isostructural with LaCo2B2 and YCo2B2, where R=Nd, Sm, Gd, Tb, and Dy. However, efforts to prepare CeCo2B2 and ErCo2B2 by arc-melting were unsuccessful.