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The magnesium alloys containing long-period stacking ordered (LPSO) structures exhibit excellent mechanical properties. Each LPSO structure is known to contain either AB′C′A or AB′C building block and feature its own stacking sequences. By atomic-scale high-angle annular dark field scanning transmission electron microscopy, we find the co-existence of AB′C′A and AB′C building block in a single LPSO structure of the as-cast Mg92Co2Y6 (at.%) alloy, leading to the formation of six new polytypes of the LPSO structures determined as 29H, 51R, 60H, 72R, 102R and 192R. The lattice parameter of each LPSO structure is derived as and (n presents the number of basal layers in a unit cell). The stacking sequences and the space groups of these newly identified LPSO structures are proposed based on the electron diffraction and atomic-scale aberration-corrected high-resolution images. A random distribution of Co/Y elements in the basal planes of AB′C′A and AB′C structural units is also observed and discussed.

Twins or multiple twins occur frequently in the orthorhombic Al20Cu2Mn3 approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al20Cu2Mn3 approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al20Cu2Mn3 approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

The microstructure of ferroelectric [PbZrxTi1� xO3/PbZryTi1� yO3]n epitaxial multilayers (x/y ¼ 0.2/0.4, 0.4/0.6) deposited on SrRuO3-coated SrTiO3 substrates by pulsed-laser deposition with different layer periodicity and layer thickness was characterized by means of transmission electron microscopy. Electron diffraction and contrast analysis revealed a very clear and well-separated layer sequence. The microstructures of PbZr0.2Ti0.8O3/ PbZr0.4Ti0.6O3 and PbZr0.4Ti0.6O3/PbZr0.6Ti0.4O3 multilayers show a similar tendency in the dependence on the individual layer thickness. Whereas with thick individual layers, tetragonal a-domains are confined to specific layers of the two types of multilayers, below a certain critical thickness of the individual layers, a-domains extend over the whole film. This indicates a transition into a uniform tetragonal lattice and strain state of the whole multilayer. Increasing the layer periodicity further, the interfaces in PbZr0.4Ti0.6O3/PbZr0.6Ti0.4O3 multilayers become rough, and complex a-domain configurations appear.