Enhanced grain growth in YBa2Cu3O7−δ doped with Ag,Cu, and CuO

Powders of YBa₂Cu₃O_7– were mixed with Ag, Cu, and CuO powders, pressed and sintered in air and oxygen. Grain-growth enhancement has been observed in the doped samples on sintering in oxygen at 980°C and its attributable to a partial melting and decomposition followed by crystallization during cooling. While the mechanisms of the partial melt may differ with dopant, grain growth enhancement appears to be a common feature of partial melt followed by slow cooling. The possibility of using suitable dopants in aiding an aligned grain structure is pointed out.     

Martensitic transformations in Ti (Ni,Fe) alloys

In this work we used x-ray structural analysis to investigate the martensitic transformations (MTs)B2R andRB19 in Ti(Ni, Fe) alloys containing 1, 2.5, 4, 5 at. % Fe, and the effect of heat treatment on the MT temperatures and sequence. In the majority of cases, it was found that the MTB2R proceeds through a two-phase region (+R). Heat treatment leads to a narrowing of the temperature interval of the existence of the two-phase region, weakly affects the onset temperatures of the MTsB2R T_R andRB19 M_s, and sharply increases the temperature-of the end of the MT M_e. The existence of the two-phase region is related to the two MT channelsB2R andB2B19 initially intrinsic to the allovs of the given compositions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 19–22, December, 1989.     

Structural investigation of phase transformations in an MnAl alloy

A comprehensive x-ray diffraction study is made of an MnAl alloy, including a phase analysis of the alloy. Changes in the lattice parameters of the phases during phase transformations are examined and an analysis is made of the dispersion of the metastable ferromagnetic -phase. The structural characteristics are studied with different annealing temperatures ranging from 450 to 900°C. The temperature sequence of the phase transformations of the alloy is determined, along with the optimum conditions for the formation of the magnetic phase in the alloy. The structural characteristics of the phases that are obtained provide evidence of a difference in the processes responsible for ordering of the - and -phases. It is shown that it is possible to use the lattice-parameter ratioc/a to study the directionality of phase transformations in the alloy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 34–38, August, 1989.     

Magnetooptical effects in bismuth-containing ferrite-garnet films

We present results of magnetooptical investigations of bismuth-containing ferrite-garnet films with the easy axis of magnetization parallel to the specimen surface. Measurements were conducted for incident light with energies in the range 1.5–3.2 eV for transverse [equatorial Kerr effect (EKE)] and for longitudinal [meridional intensity effect (MIE)] magnetizations of thin-layer specimens. It is shown that the EKE differs from zero when the films are opaque, and it is established that the EKE peak in the region 2.8 eV increases with increasing bismuth concentration. For longitudinal magnetization, conditions for observing magnetooptical interference were realized. The experimental curves agree well with the theoretical ones.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 10–14, November, 1989.     

Investigation of the character of the exchange interaction in the system Hg1−xMnxSe

A new method is proposed for determining the magnetic characteristics (magnitude and sign of the exchange interaction energy and the average size of clusters of magnetic ions) of dilute solid solutions of semimagnetic semiconductors at low temperatures based on oscillation measurements. The method makes it possible to find the magnetic characteristics of the indicated systems at temperatures between the point of the transition into the spin glass state and the temperature corresponding to the characteristic binding energy of magnetic atoms in clusters, for which standard methods based on the measurement of the magnetic susceptibility are not effective. The method is used to study the character of the exchange interaction in the system of solid solutions Hg_1–xMn_xSe as a function of their composition as well as under conditions of hydrostatic compression. To this end the oscillations of the magnetoresistance (Shubnikov-de Haas (SH) effect) in single-crystalline samples of Hg_1–xMn_xSe in the region of compositions 0.001 x 0.23 in magnetic fields H up to 65 kOe at temperatures T = (0.4–20) K and pressures up to 16 kbar were studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 29–39, November, 1989.     

Equation for the incomplete mean temperature density matrix. Application to diffusion in NQR

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 53–56, April, 1989.     

Quantum dynamics of H2 formation on a graphite surface through the Langmuir Hinshelwood mechanism

We have studied the formation of the H2 molecule on a graphite surface, when both H atoms are initially physisorbed. The graphite surface is assumed to be planar, and a model potential is obtained in a semiempirical way to reproduce the experimental properties of H physisorption on graphite. The reaction probability has been computed in the case when the angular momentum of the relative H-H motion lies parallel to the surface plane. Three-dimensional wave packet calculations have been performed for collision energies ranging from 2 to 50 meV. It is shown that the reaction occurs with a significant probability and produces the H2 molecule with a considerable amount of vibrationnal energy. A simple mechanical model is presented, where desorption of the nascent H2 molecule results from two successive binary elastic collisions.     

Arylation of 2,5-dimethyl-4-phenylpyridine

The position of the pyridine ring is arylated by reaction of 2,5-dimethyl-4-phenylpyridine with phenyllithium and p-tolyllithium. Destructive oxidation of the diaryl-substituted pyridines primarily affects the pyridine ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1359–1361, October, 1970.     

The catalytic reactions of triethyl- and triethoxy-silane with unsaturated sulphides

The hydrosilylation of mono- and di-alkenyl sulphides of the type RS(CH₂)_nCH=CH₂ (R = C₂H₅, CH₂=CH, CH₂=CHCH₂, C₃H₇, n = 0, 1 and 4) by triethyl- and triethoxy-silane, catalyzed by H₂PtCl₆·6 H₂O, (Ph₃P)₃RhCl and (PhCN)₂PdCl₂·Ph₃P, has been studied. The addition of hydrosilane to the double bond of alkenyl sulphide leads to a mixture of two isomeric monoadducts. The hydrosilane can cleave the C---S bond of the initial sulphides giving the corresponding derivatives of thiosilanes, X₃SiS(CH₂)_nCH=CH₂ (X = C₂H₅, C₂H₅O). Hydrosilylation of alkenyl sulphides is accompanied by some side reactions such as dehydrocondensation, reduction and polymerization. The effect of the catalyst nature, the structure of hydrosilane and alkenyl sulphide on the reaction route has been investigated.