Abstract
Fine particles of chromium were produced by evaporation and condensation of chromium in argon at low pressures (Kimoto et al.: Japan. J. appl. Phys. 2 (1963) 702). Electron diffraction studies have shown that the particles have the ordinary b.c.c structure of chromium when the argon contains a small amount of air or oxygen but they have a new structure when the argon is pure.
The new structure has a cubic primitive lattice with lattice constant a0=4.588±0.001 Å. The unit cell contains eight chromium atoms; the probable space group is Pm3; one atom occupies position (a) 000, one atom occupies position (b) (Remark: Graphics omitted.) and the remaining six atoms distribute themselves so that on the average one-quarter of an atom occupies each of the 24-fold position (1) xyz; where (Remark: Graphics omitted.), y=v, (Remark: Graphics omitted.) with parameters u=0.2⁄100, v=4⁄100 and w=1⁄100. This is a disordered atomic arrangement derivable from the β-tungsten structure. The shortest Cr-Cr distance is 2.34 Å.
The new modification transforms into the ordinary b.c.c. form above 400°C.
