Naoto Sumida1, Tsuneo Mishima2 and Hiroshi Fujita3
1Department of Materials Science and Engineering, Faculty of Engineering, Osaka University, Suita
A tetragonal high-temperature phase (ζα-phase) and an orthorhombic low-temperature phase (ζβ-phase) exist in iron disilicide FeSi2. Electron microscope observation shows that most of the grains in the ζβ-phase alloy have lamellae.
These lamellae produce streaks perpendicular to the (100) plane in a diffraction pattern of the  zone axis. Contrast of the lamellae in a bright field image observed from the exact  zone axis disappears completely. There is no irregularity on the periodic arrangement of bright dots in a lattice image taken from the  zone axis. Therefore, it is concluded from these results that the lamellae are not thin precipitates but stacking faults on the plane parallel to the (100) plane with the  displacement vector.
Comparing the observed lattice image taken from the  zone axis with the simulated image, the positions of bright dots are assigned to be a group of iron atom rows lying in the first and the sixth stacking plane along the  direction in the unit cell. Taking into the consideration of the crystal structure of the ζβ-phase, we suggest the stacking fault is formed by the 1/2  displacement between the third and the fourth stacking plane in the unit cell.
β-iron disilicide, lamella, stacking fault, diffraction pattern with streaks, lattice image of lamella
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