The structure of the μ-phase Co₇Mo₆

Abstract

The #-phase structure of Co,Me 6 has been confirmed by making single-crystal measurements. The atomic parameters show some significant changes when compared with those in/~F%W s, and the interatomic distances in CoTMo 8 are compared with those in other transition-metal phases. The distribution of atoms in the available sites appears to be completely ordered.

The ordering of the σ phases Cr2Ru and Cr2Os

“…The 12 sites form rows GIEI2G of a planar net where the distances between any pair of atoms, particularly 12--/2, are noticeably short compared to the sums of atomic radii of the 'compound' atoms at those sites; this has also been observed in o'-MoaCo 2 (Forsyth & Alte da Veiga, 1963). The abnormally short J-J distance, suggesting strong electronic bonding (Nevitt, 1962), has been associated with bond angles of 180 ° (Forsyth & Alte da Veiga, 1962); it is difficult, however, to explain this directional character of the bonding between identical atoms of a transition metal occupying equivalent positions in the structure.…”

HRTEM study of Co7W6 and its typical defect structure

“…Structural defects, related to mistakes in the operations mentioned above, have since long been observed in tetrahedrally close-packed compounds, like the s-phase (in the Fe±Mo [6] and Fe±Cr [7] systems) and the Mand P-phases (in the Fe±Mo [6,8] and Mo±Co±Si [8,9] systems). Twins and other planar defects which may be explained by mistakes in the alternat-ing intergrowth of the Zr 4 Al 3 and MgCu 2 sheets have in turn been observed in the Fe 7 W 6 [10], Fe 7 Mo 6 [6,8], and Co 7 Mo 6 [11,12] versions of the m-phase. However, a quantitative characterization of the defect structures was not performed in this earlier work.…”

“…The crystal structure, ®rst determined by Magneli and Westgren [3] and later re®ned for the isotypic Co 7 Mo 6 by Forsyth and D'Alte da Veiga [4], belongs to the R " 3m space group. The lattice parameters in the hexagonal system range from 0.472 to 0.475 nm for a and 2.548 to 2.567 nm for c [3].…”

μ Phase in a Nickel Base Directionally Solidified Alloy

“…With a hexagonal system, the phase belongs to a D 5 3d À R3m space group and has the rhombohedral lattice with a ¼ 0:476 nm and c ¼ 2:56 nm. [1][2][3][4][5] The presence of the phase in some nickel base alloys is unavoidable due to the high concentration of tungsten and molybdenum. Generally, when the content of tungsten and molybdenum is more than 3.5 (mol%), the phase will be the main TCP phase instead of the phase.…”