Physical metallurgy of Ti–Ni-based shape memory alloys

On the effect of alloy composition on martensite start temperatures and latent heats in Ni–Ti-based shape memory alloys

Materials simulations using VASP—a quantum perspective to materials science

Microstructure, fabrication and properties of quasicrystalline Al–Cu–Fe alloys: a review

Quasicrystals are unusual in that though aperiodic, they retain long-range crystalline order. Quasicrystalline surfaces hold tremendous interest due to their structural and chemical complexity leading to exotic properties. Mikhael et al. describe interactions between highly charged colloidal particles and a quasicrystalline surface generated through the exposure of the surface to a quasiperiodic patterned potential. They find that when the charges on the colloids are shielded, the surface acts as a template for the colloidal monolayer, which adopts order from the patterned potential to form a two-dimensional quasicrystal. But when the colloidal interactions are not shielded, transition to Archimedean tiling-like pattern occurs. In this, order is still locally commensurate with quasicrystalline structure but some of the periodicity observed when colloidal interactions dominate remains. However, over the long range, defects are now observed in a quasiperiodic pattern known as a Fibonacci chain. This is a useful colloidal model for atomic quasicrystalline systems and provides new insights into links between periodic and aperiodic crystalline order. Monolayers on crystalline surfaces often form complex structures with physical and chemical properties that differ strongly from those of their bulk phases1. Such hetero-epitactic overlayers are currently used in nanotechnology and understanding their growth mechanism is important for the development of new materials and devices. In comparison with crystals, quasicrystalline surfaces exhibit much larger structural and chemical complexity leading, for example, to unusual frictional2, catalytical3 or optical properties4,5. Deposition of thin films on such substrates can lead to structures that may have typical quasicrystalline properties. Recent experiments have indeed showed 5-fold symmetries in the diffraction pattern of metallic layers adsorbed on quasicrystals6,7. Here we report a real-space investigation of the phase behaviour of a colloidal monolayer interacting with a quasicrystalline decagonal substrate created by interfering five laser beams. We find a pseudomorphic phase that shows both crystalline and quasicrystalline structural properties. It can be described by an archimedean-like tiling8,9 consisting of alternating rows of square and triangular tiles. The calculated diffraction pattern of this phase is in agreement with recent observations of copper adsorbed on icosahedral Al70Pd21Mn9 surfaces10. In addition to establishing a link between archimedean tilings and quasicrystals, our experiments allow us to investigate in real space how single-element monolayers can form commensurate structures on quasicrystalline surfaces.

/pdf/archimedean-like-tiling-on-decagonal-quasicrystalline-xw67jor4pl.pdf

Archimedean-like tiling on decagonal quasicrystalline surfaces

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below \ensuremath{\sim}700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically identical, but symmetrically inequivalent surfaces, a model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of cubic close-packed and icosahedral-packed materials. The model explains not only the symmetries of the cubic surface terminations, but also the number and orientation of domains.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1061&context=chem_pubs

Crystalline surface structures induced by ion sputtering of Al-rich icosahedral quasicrystals

We present direct evidence of dynamical diffraction of x rays from a quasicrystal. High-resolution x-ray-diffraction measurements of the Al-Pd-Mn face-centered icosahedral quasicrystal were performed, revealing a mosaic full width at half maximum of less than 0.001\ifmmode^\circ\else\textdegree\fi{}. In a second experiment, the anomalous transmission of x rays (the Borrmann effect) was observed. These measurements show that nearly perfect quasicrystals may be grown to centimeter-size dimensions allowing x-ray techniques based upon dynamical diffraction to be brought to bear on the analysis of icosahedral structures.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1111&context=ameslab_pubs

Dynamical x-ray diffraction from an icosahedral quasicrystal.

C60 adsorption on the quasicrystalline surface of Al70Pd21Mn9

The nature of the five-fold surface of Al(70)Pd(21)Mn(9) has been investigated using scanning tunneling microscopy. From high resolution images of the terraces, a tiling of the surface has been constructed using pentagonal prototiles. This tiling matches the bulk model of Boudard et. al. (J. Phys.: Cond. Matter 4, 10149, (1992)), which allows us to elucidate the atomic nature of the surface. Furthermore, it is consistent with a Penrose tiling T^*((P1)r) obtained from the geometric model based on the three-dimensional tiling T^*(2F). The results provide direct confirmation that the five-fold surface of i-Al-Pd-Mn is a termination of the bulk structure.

D. W. Delaney

Papers

Crystalline surface structures induced by ion sputtering of Al-rich icosahedral quasicrystals

Dynamical x-ray diffraction from an icosahedral quasicrystal.

C60 adsorption on the quasicrystalline surface of Al70Pd21Mn9

Tiling of the five-fold surface of Al(70)Pd(21)Mn(9)

Tiling of the fivefold surface of Al70Pd21Mn9