Publications

Electron spin resonance investigations of the thermo-oxidative degradation of trans-polypentenamer rubbers, containing various stabilizers, are reported. The dependence of the resonance line parameters on the degradation time and temperature as well as the effect of various stabilizers on the resonance line are studied in detail. The activation energies for the generation of free radicals, the reaction order for the overall generation of free radicals and the associated constant rate, are estimated.

The structure of pollycrystalline C60 films prepared by sublimation from 99.9% pure C60 powder and from graphite soot was investigated by X-ray diffraction. A complex fcc (111) line was found in the former samples. Comparison of experimental and simulated (111) profiles allowed to assess quantitatively the degree of stacking disorder introduced during the growth of the film. Probabilities could be derived for continuation of already started fcc and hcp sequences, thereby characterizing the statistical microstructure of the C60 films. Also, the relative magnitudes of inter- and intra-layer disorder can be estimated. The films deposited from graphite soot show a high structural disorder.

The present paper is a review of the data about the dislocations in the as-grown quartz crystal. The work presents some general considerations about dislocations, their origins and causes, methods of their observation and techniques to reduce the dislocations density. It is also shown a method to obtain a new shape crystal used in the positive X-seeds preparation.

Electron spin resonance (ESR) investigations of polyethylene, irradiated with accelerated sulphur ions, are reported- The temperature dependence of resonance line parameters in the range 20-260-degrees-C, has been studied. Additional ESR data on polyethylene irradiated with neutrons as well as on polyethylene thermally degraded in air are presented. The nature of the free radicals induced by irradiation is discussed.

A method for the single crystal growth of Yttrium Iron Garnet (YIG) in a PbO/PbF2/B2O3 flux mixture with a melt cooling rate of 1-2.5 degrees C/h is described. In order to keep constant the crystal stoichiometry as well as its specific structural and magnetic properties at such high rates of the cooling process, a previously sintered polycrystalline garnet has been used as raw material. The YIG single crystal quality was checked-up by metallographic analysis, X-ray diffraction, SEM, and magnetic susceptibility measurements.

Evidence for a frozen spin ground state and a mixed magnetic ordered and paramagnetic state at intermediate temperatures was found in Fe-57-doped LiNiO2, using Mossbauer spectroscopy. The magnetic measurements, in agreement with Mossbauer data, suggest short-range ferromagnetic correlations at low temperatures and the occurrence of a paramagnetic phase below the spin freezing temperature.

In-field Mossbauer studies have been performed on the Li-0.5(1+t)(l+r)Fe2.5-1.5tTitO4 system with 1.10 less than or equal to t less than or equal to 1.40. The disordered magnetic properties depend strongly on the chemical disorder and local order induced by thermal treatments. The results are in agreement with low- and high-field magnetization measurements. Locally canted states are observed, with the degree of magnetic disorder depending on the composition and (or) the local chemical disorder.

Photoluminescence studies on Si1-xGex layers exceeding the critical thickness show not only dislocation-related peaks D1,...,D4, but also in addition a broad band (T band), centered at similar to 110 meV below the strained alloy band gap. Depth profiling studies show that the T band is due to centers in the Si1-xGex. The excitation power dependence and high quantum efficiency of the T band can be explained by assuming that it is due to an isoelectronically trapped exciton. T-band line shapes were fitted by a model based on statistical fluctuations of the Ge content and their effect on the local gap energy.

In the presence of tin tetrachloride, the rate constant for the rebinding of CO to the triliganded hemoglobin, l'(4), is much increased and the number of molecules participating in the CO ligation is decreasing. The pH drops, but a proton consumption process also takes place at the same time. The heme and its environment do not seem to change much, but the tin complexing to protein is very probable. The oxidation of hemoglobin in the form of either oxy or carbonmonoxy occurs with rather high rate.