LAUSR

Abstract 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]/[Yb] = 43.3 at 1500 °C ( Pbam space group; YB 50 -type; a = 16.5811(5) A, b = 17.5950(5) A, c = 9.4647(3) A; 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 ( F m 3 ¯ c space group; YB 66 -type; a = 23.3587(6) A). Powder X-ray diffraction data of the alloy YbB ~70 annealed at 1825 °C yielded, along with the YB 66 -type compound (a = 23.3691(2) A), β - rh B as a secondary phase ( R 3 ¯ m space group, a = 10.9298(3) A, c = 23.875(1) A), for which the solubility of Yb was found to be below 1 at%. The Yb atoms in β - rh B occupy the D and E voids. Both YbB 43.3 (YB 50 -type) and YbB 56.7 (YB 66 -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.