On the boron rich phases in the Yb-B system

Two boron rich phases were successfully synthesized by borothermal reduction of Yb oxide under vacuum. For the new boron-poorer phase, the single phase was established at around [B]ab] = 43.3 at 1500 degrees C (Pbam space group; YB50-type; a = 16.5811(5) angstrom, b = 17.5950(5) angstrom, c = 9.4647(3) angstrom; powder X-ray diffraction; Rietveld refinement). The crystal structure of the boron-richer phase ([B]/[Yb] = 56.7) has been elucidated by single crystal X-ray diffraction (Fm (3) over barc space group; YB66-type; a = 23.3587(6) angstrom). Powder X-ray diffraction data of the alloy YbB similar to 70 annealed at 1825 degrees C yielded, along with the YB66-type compound (a = 23.3691(2) angstrom) beta-rh B as a secondary phase (R (3) over barm space group, a = 10.9298(3) angstrom, c = 23.875(1) angstrom), for which the solubility of Yb was found to be below 1 at%. The Yb atoms in beta-rh B occupy the D and E voids. Both YbB(43.)3 (YB50-type) and YbB56.7 (YB66-type) feature complicated boron atom frameworks which exhibit shorter B-B separations both within and between boron clusters as compared to those observed for prototype structures.