Polytypism in alloys

This paper summarizes polytypes in alloys having layer structures such as Laves phases and Sm-Ni intermetallics which were studied by X-ray diffraction and electron microscopy. In the Mg-base pseudo-binary Laves phases, many stacking variants were found as a function of electron concentration. They are 4H, 6H, 3C, 4H, 21R, 10H, 16H, 9R, 6H', 14H, 8H and 2H in order of increasing e/a from 0.67 to 2.0. Many polytypes were also observed in the specimens of Sm₂Ni₇ and Sm₅Ni₁₉ compounds. Polytypes found in Sm₂Ni₇ are 2H, 3R, 4H, 5T, 9R, 12R, and for Sm₅Ni₁₉ 2H, 3R, 4H, 5T, 6H, 7T, 9R, 12R, 15R, 18R were recognized. Stacking faults, intergrowth and many defect structures were observed under the electron microscope.