Materials Literature
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Various iron porphyrin systems were found to catalyze the dehydration of aldoximes, such as heptanaldoxime or phenylacetaldoxime, into the corresponding nitriles under mild conditions ( t = 20 °C, neutral or slightly acidic pH). In all these systems, the presence of both the iron porphyrin catalyst and a reducing agen…
Local density calculations of the electronic structure of FeSi, FeSi_{1-x}Al_x and Fe_{1-x}Ir_xSi systems in the B20 structure are presented. Pure FeSi has a semi-conducting gap of 6 mRy at 0 K. Effects of temperature (T) in terms of electronic and vibrational excitations are included. Various measurable properties, s…
In Al-free PrBa_2Cu_3O_{7-y} single crystals the kink in the temperature dependence of magnetic susceptibility chi_{ab}(T), connected with Pr antiferromagnetic ordering, disappears after field cooling (FC) in a field H || ab-plane. The kink in chi_c(T) remains unchanged after FC in H || c-axis. As a possible explanati…
Recently, Zou et al. (Phys. Rev. Lett. 80, 1074, 1998) reported the observation of bulk superconductivity (SC) for a PrBa_2Cu_3O_x (Pr123) single crystal grown by the traveling-solvent floating zone (TSFZ) method. The aim of this Comment is to show the inconsistency of the value of effective magnetic moment μ_{eff} re…
We use a hybrid Monte Carlo algorithm in which a single-cluster update is combined with the over-relaxation and Metropolis spin re-orientation algorithm. Periodic boundary conditions were applied in all directions. We have calculated the fourth-order cumulant in finite size lattices using the single-histogram re-weigh…
The Hall resistivity rho_{xy} of LuNi_2B_2C is negative in the normal as well as in the mixed state and has no sign reversal typical for high-T_c superconductors. A distinct nonlinearity in the rho_{xy} dependence on field H was found in the normal state for T < 40K, accompanied by a large magnetoresistance reaching +…
Mesoporous titania with a large surface area has been prepared by calcination of hybrid composites. The composites were obtained by the incorporation of the biopolymer chitosan in titania networks produced from titanium isopropoxide by a sol−gel process. The resultant titania is of the pure anatase form. The effect of…
Using geometry optimizations with nonlocal density functional theory, we have carried out a broad survey of the molecular structures of porphyrin variants including inverted porphyrin, true carbaporphyrin, azuliporphyrin, and oxacarba- and thiacarbaporphyrins. For each ring system studied, we have calculated the relat…
Laser ablations were performed on C x Ni y Co y targets ( x, y = 98.8, 0.6 or 91, 4.5) using a Nd:YAG pulsed laser. Influences of the laser-beam intensity and atmospheric temperature on the structures of target surfaces and carbonaceous deposits were compared. These influences were found to be similar except for the f…
Cross-linked polycarbosilane/siloxane hybrid polymers were synthesized by sol−gel processing of both the linear and the hyperbranched alkoxy-substituted polycarbosilanes of the type “[Si(OR) 2 CH 2 ] n ”, where R = Me or Et. The molecular structure of these gels and their pyrolysis to silicon oxycarbide ceramics were…
We report results of theoretical studies on the elastic properties of single-wall nanotubes of the following compositions: C, BN, ${BC}_3$, ${BC}_2{N}$ and ${C}_3{N}_4$. These studies have been carried out using a total energy, non-orthogonal tight-binding parametrisation which is shown to provide results in good agre…
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…