Defect Structures in Al-Ni-Rh Crystalline Approximants Studied by HREM and HAADF Techniques
By means of a combination of high-resolution electron microscopy (HREM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) techniques, we have directly revealed that periodic arrangements in different manners for flattened hexagons constructed with atom columnar clusters can form two Al-Ni-Rh crystalline approximant phases. In contrast to periodic arrangements of flattened hexagons, configurations and distributions of various defects in these structurally-complicated alloy phases have been examined and their structural characteristics discussed. HREM observations clearly show that structural defects in Al-Ni-Rh crystalline approximants are of phason type and they are correlated with incorrect arrangements of atom columnar clusters. The distribution of high density planar defects can destroy the long-range periodicity in at least one direction in the pseudo decagonal symmetry plane. By means of the HAADF-STEM imaging technique, the existence of ill-formed atom columnar clusters in the core area of a linear defect, which is usually not visible in HREM observations, has been clearly revealed.
Young Won Chang, Nack J. Kim and Chong Soo Lee
W. Sun et al., "Defect Structures in Al-Ni-Rh Crystalline Approximants Studied by HREM and HAADF Techniques", Materials Science Forum, Vols. 561-565, pp. 1353-1356, 2007