Materials Literature
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A quantitative analysis is presented of the increasing degree of dynamical correlations with decreasing temperature in a fragile glass-former consisting of a two-dimensional binary mixture of soft discs with a diameter ratio of . The analysis involves a study of the spatial distribution of local relaxation times, defi…
Pulsed-laser deposited (PLD) polytetrafluoroethylene (Teflon-PTFE) films from press-sintered powder targets are found to be highly crystalline, with spherulite sizes adjustable over more than one order of magnitude by suitable thermal annealing. Films with large spherulites show an excellent charge stability, comparab…
Pure Fe powders, milled down to 10 nm crystallite size, have been analyzed by a combination of M\"ossbauer spectroscopy, high resolution transmission electron microscopy, and magnetization measurements. After annealing the as-milled powders at 570 K for 1 hour, a new phase is identified with a hyperfine field of 21 T,…
The luminescence properties of silicon nanocrystals fabricated by Si ion implantation into a SiO2 matrix and subsequent thermal annealing have been studied. To identify the mechanism of photoluminescence of Si nanocrystals, the dependencies of the steady-state photoluminescence on temperature and excitation power dens…
The CaS:Sm3+ nanocrystallites are synthesized by the modified sol-gel technique. The grain size of the nanocrystallites is approximately 60 nm, which is determined by transmission electron microscopy, x-ray diffraction and UV-vis absorption spectrum. Compared to the CaS:Sm3+ macrocrystallites, the absorption and emiss…
The polydispersive dielectric response of the relaxor ferroelectric lead magnesium niobate was investigated using nonresonant spectral hole-burning experiments. Using large alternating electric fields, specific parts of the relaxation-time distribution could be addressed selectively. This provides evidence for the dyn…
Sm–Co-type alloys were disproportionated by milling in hydrogen at enhanced temperatures. X-ray diffraction confirmed the disproportionation of the SmCo5 and Sm2Co17 phases into Sm hydride and α-Co. This “reactive milling” procedure facilitates the disproportionation of these alloys which are characterized by a very h…
Electronic structure calculations for MgO, MgS and are reported. It is shown that the conduction bands of MgO and MgS have predominantly anion character, contrary to the common picture of the conduction band being derived from cation states. In transition metal oxides, unoccupied anion states are less important due to…
The infrared absorption of charge density waves coupled to a magnetic background is first observed in two manganites ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ with $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.5$ and $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.67$. In bo…
Structural, magnetic, and transport properties of polycrystalline La0.7Ca0.3Mn1−xFexO3 and La0.7Ca0.3Mn1−xGexO3 are experimentally studied. Single-phase samples are obtained in the range x=0–0.12 for Fe, and x=0–0.06 for Ge. There are no appreciable structure changes due to the introduction of Fe and Ge. The Mn-site d…
Rigid and flexible linkers are combined in the new dendrimer shown schematically in the picture, which contains nine metalloporphyrin units (Porph). The construction is such that the four "arms" of the dendrimer can fold in a cooperative and predetermined manner in response to added 1,4-diazabicyclo[2.2.2]octane (DABC…
Several homologs of new liquid crystals of strongly bent, achiral molecules have been investigated by optical second harmonic generation. It is shown that the initial nonpolar mesophase is converted into a polar state, which leads to frequency doubling of optical waves by applying electric fields of a few $\mathrm{V}/…
Channels make up 46% of the crystal volume: A two-dimensional coordination polymer of exceptional structural regularity (see schematic drawing; tpp=tetraphenylporphyrin, tpyp=tetrapyridylporphyrin) was assembled from [MnIII(tpp)]⋅ClO4 and tpyp. The crystal packing of these polymers yields an open bulk structure with n…
A large enhancement in the thermoelectric figure of merit for the whole superlattice, Z3DT, is predicted for short-period GaAs/AlAs superlattices relative to bulk GaAs. Various superlattice parameters (superlattice growth direction, superlattice period, and layer thicknesses) are explored to optimize Z3DT, including q…
The effect of incoherent interlayer transport on the interlayer resistance of a layered metal is considered. We find that for both quasi-one-dimensional and quasi-two-dimensional Fermi liquids the angular dependence of the magnetoresistance is essentially the same for coherent and incoherent transport. Consequently, t…
The intrinsic coercivity Hci in Sm(CobalCuxFe0.1Zr0.033)z powder materials was found to increase with increasing temperature when Cu content x=0.048, but to decrease when Cu content x⩾0.068. This abnormal behavior, which is also reversible, was found in a series of samples with various ratios z. The field dependence o…
Up to 14 porphyrin rings are present in the title compounds 1, which are readily available with high regioselectivity from linear nickel-zinc porphyrins. Upon irradiation with light a rapid energy transfer from the peripheral porphyrin rings to the diporphyrin core takes place.
Using molecular dynamics computer simulations we investigate how the relaxation dynamics of a simple supercooled liquid with Newtonian dynamics differs from the one with a stochastic dynamics. We find that, apart from the early $\ensuremath{\beta}$-relaxation regime, the two dynamics give rise to the same relaxation b…
We calculated the effects of structural distortions on the electronic structure of carbon nanotubes. The key modification of the electronic structure brought about by bending a nanotube involves an increased mixing of $σ$ and $π$-states. This mixing leads to an enhanced density-of-states in the valence band near the F…
In order to resolve the controversy about the low density region of the phase diagram of the 4He monolayer on graphite, we have undertaken a path integral Monte Carlo study of the system. We provide direct evidence that the low density monolayer possesses solid clusters and a low density vapor as opposed to the most r…