Title: An X-Ray Investigation of the Nickel-Boron System. The Crystal Structures of Orthorhombic and Monoclinic Ni4B3.
Abstract:The Ni-B system was investigated with x-ray powder and single-crystal methods in the range Ni/sub 3/B to NiB. In addition to the previously known intermediate phases, Ni/sub3/B, Ni/sub 2/B, and NiB, t...The Ni-B system was investigated with x-ray powder and single-crystal methods in the range Ni/sub 3/B to NiB. In addition to the previously known intermediate phases, Ni/sub3/B, Ni/sub 2/B, and NiB, the existence of two other phases, both with the ideal compositions Ni/sub 4/B/sub 3/ but one orthorhombic and the other monoclinic, was established. The following two-phase regions were found: Ni/sub 3/B + Ni/sub 2/B, Ni/sub 2/B + orthorhombic Ni/sub 4/B/sub 2/, orthorhombic Ni/sub 4/B/sub 3/ + mo noclinic Ni/sub 4/B/sub 3/, and monoclinic Ni/ sub 4/B/sub 3/ + NiB. The unit cell of orthorhombic Ni/sub 4/B/sub 3/ varies slightly with composition. The dimensions in two-phase Ni/sub 2/B + orthorhombic Ni/sub 4/B/sub 3/ alloys are the following: alpha = 11.953 A, b = 2.981 A, and c = 6.569 A and in two-phase orthorhombic Ni/sub 4/B/sub 3 + monoclinic Ni/sub 4/ B/sub 3/ alloys: a = 11.973 A, b = 2.985 A, and c = 6.584 A. The unit cell dimensions of monoclinic Ni/sub 4/B/sub 3/ are a = 6.430 A, b = 4.882 A, c = 7.818 A, and beta = 103 deg 18'. No unit cell variation of the latter phase was found. The crystal structures of themore » two new phases were determined and refined from single-crystal intensity data. The space group of orthorhombic Ni/ sub 4/B/sub 3/ is P n m a. The unit cell contains sixteen nickel atoms and twelve boron atoms situated in 4(c) positions. Two-thirds of the boron atoms form infinite zig-zag chains, while onethird have no close boron contacts. There are probably boron vacancies in the structure. The space group of monoclinic Ni/sub 4/B/sub 3/ is C 2/c. Sixteen nickel atoms are situated in two 8 (f) positions, eight boron atoms in one 8 (f) position and four boron atoms in one 4(e) position. All boron atoms are connected in infinite chains. (auth)« lessRead More