An Electron Diffraction Study on the Crystal Structure of a New Modification of Chromium

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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 a_0=4.588 ± 0.001 A. The unit cell contains eight chromium atoms; the probable space group is Pm3; one atom occupies position (a) 000, one atom occupies position (b) 1/2 1/2 1/2 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 x=1/4-〓, y=υ, z=1/2+w with parameters u=0.2/100, υ=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 A. The new modification transforms into the ordinary b.c.c. form above 400℃.
社団法人日本物理学会の論文
1967-03-05