Molecular structure of dibenzomethylphosphonyl-2-crown-7 in the crystalline state and in solution

Conclusions A conformation is found for dibenzomethylphosphonyl-20-crown-7 in the crystalline state and in solution which is unfavorable for cooperative binding with acceptors.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1775–1779, August, 1985.The authors thank G. V. Sazonov for assistance in carrying out this work.     

Conformational analysis of dimethyl(bromomethyl)- and dimethyl(iodomethyl)phosphine oxides

Conclusions The oxides of dimethyl(bromomethyl)- and dimethyl(iodomethyl)phosphines exist as equilibrium mixtures of conformer pairs in solution, the form predominating in nonpolar solvents being that in which the phosphoryl and carbon-halogen bonds are in trans orientation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1292–1296, June, 1981.     

Kinetics of growth of carbon fibers on an iron catalyst in methane pyrolysis: A measurement procedure with the use of an optical microscope

A procedure was developed for measuring the kinetic parameters of growth of carbon fibers in the catalytic pyrolysis of hydrocarbons. In this procedure, the dependence of the averaged length of grown fibers on growth time is constructed based on the measurements of fiber lengths with an optical microscope. The procedure proposed allowed us to reliably determine the Arrhenius parameters of the rate of fiber growth and the induction period of fiber nucleation in the measurement of carbon fibers 100 nm or more in diameter. The kinetics of growth of carbon fibers from methane-hydrogen mixtures on an iron catalyst was measured over a temperature range of 950–1050°C. It was found that the rate of fiber growth as a function of methane activity in the gas phase exhibited a maximum in the activity range 200–300; the value of this maximum depends on the contribution of the products of gas-phase methane pyrolysis to the growth of fibers. It was also found that the rate of fiber growth dramatically increased as the critical concentration of pyrolysis products in the mixture was reached. This increase was interpreted as a change from one growth mechanism (growth from methane) to another growth mechanism (growth from acetylene). The experimental data explained the high sensitivity of the process of carbon fiber growth from methane to temperature and the residence time of the gas in the reactor.     

Thermophysical study of structural phase transitions in Na<Subscript>0.95</Subscript>Li<Subscript>0.05</Subscript>NbO<Subscript>3</Subscript> solid solution

Temperature dependences of specific heat C_p(T) and coefficient of thermal expansion ;(T) for Na_0.95Li_0.05NbO₃ sodium-lithium niobate ceramic samples are investigated in the temperature range of 100–800 K. The C_p(T) and α(T) anomalies at T₃ = 310 ± 3 K, T₂ = 630 ± 8 K, and T₁ = 710 ± 10 K are observed, which correspond to the sequence of phase transitions N ? Q ? S(R) ? T2(S). The effect of heat treatment of the samples on the sequence of structural distortions was established. It is demonstrated that annealing of the samples at 603 K leads to splitting of the anomaly corresponding to the phase transition Q → R/S in two anomalies. After sample heating to 800 K, the only anomaly is observed in both the C_p(T) and ;(T) dependence. Possible mechanisms of the observed phenomena are discussed.     

One approach to solving the basic equation of magnetostatics in the case of nonhomogeneous magnets

We propose a general approach for solving the basic magnetostatic equation in the case of nonhomogeneous magnetic solids when their magnetic permeability depends on the coordinates. Seeking the strength of the resulting field reduces to finding two scalar functions satisfying a system of one integral and one differential equation with certain boundary conditions. Using this approach, we obtain an analytic solution of the magnetostatic equation for a ball with a model permeability in an arbitrary external field.     

The role of the spatial distribution of local polarization perturbations in the posistor effect onset

The electrical resistance of polycrystalline ferroelectric semiconductors is defined by the potential barriers due to the existence of local charged surface states at crystallite boundaries. The barrier screening depends on the state of the ferroelectric system and is maximal during spontaneous-polarization switching. It is shown in this paper that the local perturbation of the ferroelectric system, resulting from the repolarization and appearing as a domain wall between the regions with different polarization directions, has a zigzag configuration. The electric field in the vicinity of the zigzag domain wall is stabilized and coincides with the coercive field, which provides low potential barriers in the ferroelectric phase compared with the paraelectric phase. The repolarization processes become inefficient in the potential barrier screening at the transition from the ferroelectric to the paraelectric phase. As a result, a sharp increase in the electrical resistance is observed at the ferroelectric-paraelectric phase transition, called the posistor effect.