New Electrochemically Active Highly Sulfurized Polyconjugated Polymers

The electrochemical activity of new highly sulfurized polyconjugated polymers is studied. The polymers, polythienothiophene, poly(4,5,6,7-tetrathieno-4,5,6,7-tetrahydro-2,3-dehydrobenzothiophene), poly(6-methylthieno[2,3-b]pyridine-4-thione-5-thiol), and poly(6H-thieno[2,3-b]-azepine-6,7(8H)-dithione) are obtained in a deep sulfurization of polyethylene, polystyrene, and poly(5-vinyl-2-methylpyridine) by elemental sulfur. Employed as active cathodic material in lithium batteries, these polymers ensure their prolonged cycling with specific discharge capacity of up to 339 mA h/g. The effect of the conducting additive and electrolyte on the energy capacity and cycling of polymer cathodes in lithium batteries is discussed.     

Direct dark matter search with CRESST and EURECA

The current status of the direct Dark Matter experiments CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) and the planned EURECA (European Underground Rare Event Calorimeter Array) is presented. Both experiments are aimed at the direct detection of WIMPs (Weakly Interacting Massive Particles), potential candidates for the Dark Matter in the universe. New design developments of the cryogenic detectors operated at mK temperatures are investigated to optimize detector performance and to simplify mass production. Thus, CRESST is also providing a basis for the EURECA project, aimed at a ton of cryogenic detectors with a multi-material target.     

Sulfurization of polymers

Polydiethylsiloxane reacts with elemental sulfur at 300–320 °C (ZnCl₂ slightly accelerates the process) with evolution of hydrogen sulfide and formation of black lustrous paramagnetic powders (sulfur content up to 38.50%), which possess a noticeable electric conductivity (3.20·10⁻⁷ S cm⁻¹ when doped with I₂) and redox properties. Polydimethylsiloxanes are stable under the same conditions. In rechargeable lithium batteries, the sulfurized polydiethylsiloxane behaves as an active cathode material allowing charging and discharging of the battery. The specific capacities of the cathodic and anodic processes (80–100 (mA h) g⁻¹) change insignificantly. The hydrolytic stability, elemental analysis, IR and ESR spectra, DSC-TGA and derivatographic analyses data, the electric conductivity, and the character of the electrochemical activity of the polymers synthesized indicate that the polymers contain the polyvinylene disulfide blocks cross-linked by the polysiloxane chain.     

Impurity-induced core-valence lumionescence: A new possibility for fast scintillators creation

The impurity-induced core-valence lumionescence (CVL) originating from the radioactive recombination os valence electrons with the uppermost core holes of the impurity is studied in a number of chlorides doped with cesium. A correlation is established between the spectra shape and the local symmetry of the nearest-neighbor anion environment of the CVL-active impurity cation. This proves the cluster nature of the emission mechanism. Cluster calcualtions of the impurity-induced CVL spectra are in good agreement with the experimental results thus supporting the validity of cluster approach to the CVL. Peculiarities of the impurity-induced CVL excitation mechanism are considered. The effect of energy transfer from hist matrix cations to CVL-active ones due to core excitation migration is discussed. Prospects of searching for efficient fast scintillators based on the impurity-induced CVL are examined.     

Mesomorphism and the effect of an electric field on the conductivity of the mesophases of lithium, sodium, and potassium 4-(trifluoromethyl)-3,6-dioxaperfluorooctanesulfonates

Mesophases were established for the first time in sodium and potassium 4-(trifluoromethyl)-3,6-dioxaperfluorooctanesulfonates (R_ofSO₃ ⁻) and in their binary systems Na,K/R_ofSO₃(I) and Na/NO₃,R_ofSO₃(II). An increase in the temperature range of the mesophase was detected in system (I). The application of an electric field increases the conductivity of the mesophase. For the isotropic Na,K/R_ofSO₃ melts an anomalous conductivity isotherm was obtained for the first time. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 234–238, July–August, 1997.     

Dielectric response function of GaPAs solid solutions in the vibrational absorption region

By taking spectra of IR transmission and reflection, attenuated total reflection, and Raman scattering, different models of the dielectric response function of GaPAs solid solutions are tested. It is demonstrated that the models accounting for the difference in the times of transverse and longitudinal vibrational relaxations, as well as the frequency distribution of TO phonons, make possible the prediction of the experimental spectra with a reasonable accuracy.     

Sulfurization of polymers

Polyethylene exhaustively sulfurized with elemental sulfur shows paramagnetic (spin concentration 2.7–9.7·10¹⁹ sp g⁻¹,g=2.0041–2.0045, ΔH=0.53–0.62 mT) and redox properties, which was demonstrated by both voltammetric and chemical methods (sodium reduction in liquid ammonia). The high concentration of unpaired electrons, the character of the electrochemical activity, and the chemical properties are in agreement with the presence in the polymers of polyconjugated ladder polythiophene and parquet polynaphtho-thienothiophene structures along with polyene-polysulfide blocks. The use of the polymers under consideration as an active cathode material in lithium batteries enables their repeated cycling with a specific charge capacitance of 150–340 mA hg⁻¹.     

Two-photon excitation and luminescence of a CaWO4 scintillator

Luminescence of a CaWO₄ scintillator was studied in the temperature range 77–500 K using intense laser excitation in the 450–600 nm spectral region. Characteristics of the observed blue emission are similar to those of the intrinsic luminescence of calcium tungstate. The emission is concluded to be caused by cascade excitation of CaWO₄ that results in a two-photon excited (TPE) luminescence. The features of TPE luminescence of CaWO₄ are analysed in comparison to those obtained with UV and X-ray excitation.     

Surface structure of finely dispersed iron powders 4. Structure of a methylvinyldichlorosilane-modified coating

The surface structure of finely dispersed iron powders treated with methylvinyldichlorosilane vapors under vacuum has been examined by X-ray photoelectron spectroscopy, including chemical derivatization of functional groups. It is shown that the hydrolysis and condensation of modifier molecules lead to the formation of multilayer coatings (40–50 Å thick) consisting of methylvinyldichlorosilane oligomers. The modifier molecules are grafted onto the surface mainly owing to the formation of oxane Si---O---Fe bonds. A high degree of ordering is characteristic of the modifier molecules in the grafted layer, whereas a thin layer adjacent to the stabilizing coating surface exhibits a high extent of oligomerization of methylvinyldichlorosilane vinyl groups. Illumination (wavelength λ 35O nm) initiates the polymerization of vinyl groups in the grafted layer bulk. In this case the degree of oligomerization amounts to 80%.