Nanostructured crystals of Sr1?xRxF2+x fluorite phases and their ordering: 6. Microindentation analysis of crystals

Hardness, crack resistance, brittleness, and effective fracture energy have been studied for crystals of 24 fluorite phases Sr_{1 − x} R _x F_{2 + x} (R are 14 rare earth elements (REEs); 0 < x ≤ 0.5) and SrF2 grown by the Bridgman method from a melt. These characteristics change nonlinearly with an increase in the REE content for Sr_{1 − x} R _x F_{2 + x} (0 < x ≤ 0.5) with R = La, Nd, Sm, Gd, and Lu; it is maximum in the range x < 0.1 for all REEs. The changes in a number of REEs have been traced for an isoconcentration series of Sr_0.90 R _0.10F_2.10 crystals (R = La, Nd, Sm, Gd, Ho, Er-Lu, or Y) and crystals (similar in composition) with R = Tb and Dy. The hardness of Sr_{1 − x} R _x F_{2 + x} crystals is higher by a factor of ∼2–3 than that of SrF2. The effect of decrease in microstresses in SrF₂ crystals is confirmed by the isomorphic introduction of R ³⁺ ions into this crystalline matrix.     

Confinement effects for ionic carriers in SrTiO3 ultrathin films: first-principles calculations of oxygen vacancies

One-dimensional confinement effects are modelled within the hybrid HF-DFT LCAO approach considering neutral and single-charged oxygen vacancies in SrTiO(3) ultrathin films. The calculations reveal that confinement effects are surprisingly short-range in this partly covalent perovskite; already for film thickness of 2-3 nm (and we believe, similar size nanoparticles) only the surface-plane defect properties differ from those in the bulk. This includes a pronounced decrease of the defect formation energy (by ～1 eV), a much deeper defect band level and a noticeable change in the electronic density redistribution at the near-surface vacancy site with respect to that in the bulk. The results also show that the size effect pertains to the interactions between the oxygen vacancy and two neighboring titanium atoms and orientation (parallel or perpendicular to the surface) of the Ti-V(O)-Ti complex. In particular, we predict considerable oxygen vacancy segregation towards the surface.     

Thermoelectric properties of a plasma at megabar pressures

A nonideal hydrogen plasma is theoretically studied for the first time as the working medium of a thermoelectric generator. A method is proposed for the calculation of the electrical conductivity, Seebeck coefficient, and thermal conductivity of the nonideal plasma in a wide range of densities and temperatures, including the region of strong degeneracy of electrons, which is achieved in experiments on the quasi-isentropic compression of deuterium and where a “plasma phase transition” (transition with a sharp change in the component composition) is possibly implemented. In this method, the kinetic coefficients are calculated together with the equation of states of the nonideal plasma. It is shown for the first time that the Seebeck coefficient in such a medium reaches 5500 μV/(K cm), which is an order of magnitude larger than that in currently available semiconductor materials used in thermoelectric generators. It is found that the figure of merit in hydrogen, which has a high thermal conductivity, at megabar pressures reaches 0.4, which is only slightly below that in currently available semiconductor materials.     

Reactions of Halides of Tervalent Phosphorus with Imines and -Diimines

Abstract

Isobutylidenebutylamine reacts with phosphorus trichloride in the presence of organic bases to give N-butyl-N-isobutenylamidodichloro-or bis(N-butyl-N-isobutenylamido)chlorophosphites depending on the ratio of reagents. Reasons are given in Eavour of the reaction beginning with the nucleophilic attack of the nitrogen atom of the imine on the electrondeficient phosphorus atom of the chloride. Reactions of ethyldichloro- and diethylchlorophosphites with benzylidenmethylamine produce 2-chloro- and 2-ethyl-2-oxo-1,4,2-diazaphospholanes respectively. Interaction of diethylchlorophosphite with benzylidenmethylamine in the presence of triethyphosphite results in the formation of diethyl. (N-methyl-N-α-diethylphosphonobenzylamido)phosphite. As a result of interaction of bis(diethylamino)chlorophosphine with NIN-dibutyl-2,3-butandiimine in the presence of triethylamine new compounds (2-diethylamino-1,3-dibutyl-4,5-dimethyl-1,3,2-diazaphospholane and 4,8-dibutyl-3,7-bis(diethylamino)-[3.3.01-bicyclooctadiene-l15) are obtained. The structure of the latter is proved by means of ¹H, ³¹ p NMR-spectroscopy, and a complete X-ray analysis. Alkyldichlorophosphines form phosphonium salts of 1,3,2-diazaphospholene structure with a-diimines and 2-chloro-1,3-dicyclohexyl-4-chloro-1,3,2-diazaphospholene resulting from the reaction of N,N-dicyclohexylethylenediimine with PCl₃. In this product the P-C1 bond is unusually long, which is confirmed by X-ray analysis. In the course of the interaction of tervalent phosphorus halides with α,β-unsaturated imines a new reaction has been discovered with the formation of 1,2-dihydro-1,2-azaphosphorines.     

Electrical Conductivity of Noble Gases at High Pressures

We present experimental and theoretical results for the electrical conductivity of noble gases (He, Ne, Ar, Kr, Xe) up to high pressures where a transition from nonmetallic to metallic‐like conductivities occurs. In addition, we show the behavior of the thermal conductivity and thermopower for xenon as an example. The experiments were performed using explosively driven shock waves. Different geometries allow to probe various parameter regions up to several megabars. Besides single‐shock experiments along the principal Hugoniot curve, also multiple‐shock experiments were performed which follow almost an isentrope. The theoretical calculations were performed within a partially ionized plasma model. The composition is determined by solving a system of mass action laws. The transport coefficients are calculated within linear response theory taking into account the relevant scattering mechanisms of electrons at different ion species, atoms, and other electrons. The general trends of the experimental results can be explained within this theoretical approach. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measurements of the electron concentration and conductivity of a partially ionized inert gas plasma

A theoretical model for the resonant hyper-Raman scattering in semiconductor crystals is presented. The Wannier excitons are considered as intermediate states. The expressions for the resonant hyper-Raman scattering cross section are obtained. The theoretical model developed allows taking into account different mechanisms of the exciton-photon and exciton-phonon interactions.     

Physicochemical Study of Ta2O5 and SiO2-Ta2O5 Film Formation from Film-Forming Solutions

In order to study physicochemical processes of formation of Ta₂O₅ and SiO₂-Ta₂O₅ films from film-forming solutions, the properties of these solutions, and also the thermal-oxidative breakdown and the properties of the obtained films, were studied.