73 research outputs found
A complicated quasicrystal approximant â16 predicted by the strong-reflections approach
The structure of the quasicrystal approximant â16 was predicted by the strong-reflections approach based on the known approximant â6
Crystal growth of copper-rich ytterbium compounds: The predicted giant unit cell structures YbCu4.4 and YbCu4.25
Two new phases YbCu4.4 and YbCu4.25 are found as a result of careful phase
diagram investigations. Between the congruent and peritectic formation of
YbCu4.5 and YbCu3.5, respectively, the phases YbCu4.4 and YbCu4.25 are formed
peritectically at 934(2)degC and 931(3)degC. Crystal growth was realised using
a Bridgman technique and single crystalline grains of about 50-100 10^{-6}m
were analyzed by electron diffraction and single crystal X-ray diffraction. Due
to the only slight differences in both compositions and formation temperatures
the growth of larger single crystals of a defined superstructure is
challenging. The compounds YbCu4.4 and YbCu4.25 fit in Cerny`s (J. Solid State
Chem. 174 (2003) 125) building principle {(RECu5)n(RECu2)} where RE = Yb with n
= 4 and 3. YbCu4.4 and YbCu4.25 base on AuBe5/MgCu2-type substructures and
contain approximately 4570 and 2780 atoms per unit cell. The new phases close
the gap in the series of known copper-rich rare earth compounds for n = 1, 2
(DyCu3.5, DyCu4.0) and n = 5 (YbCu4.5, DyCu4.5)
Chemical contrast in STM imaging of transition metal aluminides
The present manuscript reviews recent scanning tunnelling microscopy (STM) studies of transition metal (TM) aluminide surfaces. It provides a general perspective on the contrast between Al atoms and TM atoms in STM imaging. A general trend is the much stronger bias dependence of TM atoms, or TM-rich regions of the surface. This dependence can be attenuated by the local chemical arrangements and environments. Al atoms can show a stronger bias dependence when their chemical environment, such as their immediate subsurface, is populated with TM. All this is well explained in light of combined results of STM and both theoretical and experimental electronic and crystallographic structure determinations. Since STM probes the Fermi surface, the electronic structure in the vicinity of the Fermi level (EF) is essential forunderstanding contrast and bias dependence. Hence, partial density of states provides information about the TM d band position and width, sâpâd hybridization or interactions, or charge transfer between constituent elements. In addition, recent developments in STM image simulations are very interesting for elucidating chemical contrast at AlâTM alloy surfaces, and allow direct atomic identification, when the surface does not show too much disorder. Overall, we show that chemically-specific imaging is often possible at these surfaces
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