The magnetic susceptibilities of NO and OH

A non-isothermal kinetic equation for the distribution function of a sub-system weakly coupled to a bath is derived by modification of the analysis and assumptions of a previous paper [1]. The equation has the form of a generalized non-isothermal Fokker-Planck equation when it is linearized in thermodynamic gradients and only terms through second order in the coupling parameters are retained. Higher order terms in the coupling parameter do not diverge with time. The equation is compared with certain ‘exact’ model results of Ullersma and with the coherence time method. The equation is used to calculate a jump rate for diffusion of a harmonic particle weakly coupled to a lattice and it is found that the jump rate becomes independent of the mass of the particle for a heavy enough particle. The source of the discrepancy of this result with a similar calculation of Prigogine and Bak is indicated. The model of the jump rate is inappropriate for diffusion in a thermal gradient and more appropriate models of the jump are briefly considered. A brief comparison of the derivation of the kinetic equation with the Fano coherence time approximation is made and a difference is noted.     

Photo-induced change of viscosity of glassy selenium below its glass transition temperature

The viscosity of g-Se at temperatures between 25 °C and glass transition temperature of g-Se, T_g, was measured by the thermomechanical analysis (TMA). The samples were exposed by halogen light, which passes through penetration silica indentor. The exposure leads to higher rate of penetration.The viscosity of the g-Se decreased during exposure of the samples near its T_g. The photo-induced change of viscosity decreased with increasing temperature. The photo-induced decreasing of viscosity depended on intensity and wavelength of exposure light. Process of the photo-induced change of viscosity was not stable. The Raman spectra revealed that the process of photo-induced decrease of viscosity is not connected with changes of g-Se structure.     

High temperature superconductivity in sulfur and selenium hydrides at high pressure

Due to its low atomic mass, hydrogen is the most promising element to search forhigh-temperature phononic superconductors. However, metallic phases of hydrogen are onlyexpected at extreme pressures (400 GPa or higher). The measurement of the recordsuperconducting critical temperature of 203 K in a hydrogen-sulfur compound at 160 GPa ofpressure [A.P. Drozdov, M.I. Eremets, I.A. Troyan, arXiv:1412.0460[cond-mat.supr-con] (2014); A.P. Drozdov, M.I. Eremets, I.A. Troyan, V.Ksenofontov, S.I. Shylin, Nature 525, 73 (2015)], shows that metallization ofhydrogen can be reached at significantly lower pressure by inserting it in the matrix ofother elements. In this work we investigate the phase diagram and the superconductingproperties of the H-S systems by means of minima hopping method for structure predictionand density functional theory for superconductors. We also show that Se-H has a similarphase diagram as its sulfur counterpart as well as high superconducting criticaltemperature. We predict H₃Se to exceed 120 K superconductivity at 100 GPa. We showthat both H₃Se andH₃S, due to thecritical temperature and peculiar electronic structure, present rather unusualsuperconducting properties.     

Relaxation behavior of glassy selenium

The dynamics of the glass transition of amorphous selenium was investigated by using differential scanning calorimeter. The heat capacity data were analyzed applying the phenomenological Tool–Narayanaswamy–Moynihan (TNM) model in order to describe the relaxation behavior of a-Se. The TNM parameters were evaluated by fitting the enthalpic cycles and also one isothermal experiment. Furthermore, peak-shift method and several other methods of evaluating the TNM parameters were applied to confirm the results of curve fitting. The results are compared with the other published enthalpy and viscosity data, volume and enthalpy relaxation are compared on account of our previous mercury dilatometry measurements. We found out that the pre-exponential factor A and the apparent activation energy Δh^* of structural relaxation are similar for volume and enthalpy relaxation and Δh^* is very close to the activation energy of viscous flow.     

The intrinsic low temperature magnetic and transport properties of NiAl

The magnetic susceptibility, resistivity, magnetoresistance, and NMR properties of very pure stoichiometric NiAl samples have been measured. The Kondo-like phenomena previously observed in this material are absent suggesting that the intrinsic properties agree with a simple Fermi surface as predicted by APW calculations.     

Vibrational states of glassy and crystalline orthoterphenyl

Low-frequency vibrations of glassy and crystalline orthoterphenyl are studied by means of neutron scattering. Phonon dispersions are measured along the main axes of a single crystal, and the corresponding longitudinal and transversal sound velocities are obtained. For glassy and polycrystalline samples, a density of vibrational states is determined and cross-checked against other dynamic observables. In the crystal, low-lying zone-boundary modes lead to an excess over the Debye density of states. In the glass, the boson peak is located at even lower frequencies. With increasing temperature, both glass and crystal show anharmonicity. Received 7 December 1999     

The entropy difference between the Lennard-Jones crystalline and glassy states

Entropy changes of isochoric Lennard-Jones fluid-crystal and fluid-glass transitions, calculated by molecular dynamics and integration of $\text{d}\text{S =}\text{d}\text{Q}\text{T}$, are approximately equal. The entropy difference between crystal and glass, at the same density and temperature, is thus negligibly small.     

Nearly frictionless transport of glassy solid helium at low temperature regime

Glassy matter, as subjected to high shear rates, exhibit shear-thinning: i.e., the viscosity diminishes with increasing shear rate. One possible outcome for almost vanishing viscosity is the nearly frictionless transport in micropores subjected to some surface conditions. Here we show that, by treating the glass as a shear-thinning matter and using the transition rate dependent model together with the boundary perturbation method, we can observe a sudden change of the shearing characteristics (which directly relates to the resistance and the time or rate dependent shear modulus) at low temperature regime (ranged from 30 to 50 mK) for corresponding physical activation energy. If the solid helium could be treated as glassy matter at very low temperature regime then our results resemble those recently reported by Day and Beamish [J. Day, J. Beamish, Nature 450 (2007) 853].     

Fabrication of crystalline selenium microwire

A method of fabricating selenium(Se) microwire is demonstrated.A multimaterial fiber with amorphous selenium(a-Se) core and multicomponent phosphate glass cladding is drawn by using a conventional optical fiber drawing technique.Then the a-Se core of the fiber is crystallized by a post thermal process at 150 ℃.After the multicomponent phosphate glass cladding is stripped from the multimaterial fiber by marinating the fiber in HF acid solution,a crystalline selenium(c-Se)microwire with high uniformity and smooth surface is obtained.Based on microstructure measurements,the c-Se microwire is identified to consist of most hexagonal state particles and very few trigonal state whiskers.The good photoconduction property of c-Se microwire with high quality and longer continuous length makes it possible to apply to functional devices and arrays.     

The low temperature magnetic properties of potassium holmium double tungstate

The magnetic investigations of potassium holmium double tungstate KHo(WO₄)₂ have been performed. The results of measurements of magnetic susceptibility and magnetization as a function of both temperature (T = 0.5–100 K) and magnetic field (up to 2 T) are presented.     

On the mechanism of low temperature radiolysis of crystalline ice

Abstract

The free radicals from γ-radiolysis of crystalline ice with additions of alcohols and alkali hydroxides at 77 °K have been studied by EPR and optical spectroscopy methods. It has been found that trapped electrons are formed in these systems. In the case of alcohol additions it has been shown by optical spectroscopy that the electrons are stabilized in traps consisting of molecules of impurities. The yield of radicals is increased with the growth of concentration of additions and is dependent on sample structure. The mechanism of radiation chemical processes in crystalline ice is discussed.     

The critical temperature in mode coupling theory and magnetic resonance data on molecular dynamics in glassy liquids

For different molecular glass-forming liquids the critical temperaturesT _c predicted by the mode coupling theory of glass transition are compared with the temperaturesT _b at which a single relaxation process seems to bifurcate into slow and faster relaxations. The latter temperatures are taken from the magnetic resonance data available in the literature. Both temperatures coincide within experimental accuracy.     

New crystalline phases of an equiatomic K-Cs alloy at low temperature

Solid equiatomic K-Cs alloys have been investigated by X-ray diffraction throughout the temperature range 300-100K. The results indicate that a phase separation occurs below 185K accompanied by the appearance of an ordered phase in this range. This phase has a hexagonal lattice with parameters: a = 9.32(1) Å and c = 11.80(2) Å (at 170K). Evidence from our other studies [7] indicates that its composition is K₂Cs. Another phase transformation in this ordered crystal is observed below 120K. There is no change of lattice symmetry but the unit cell constants shrink to the values: a = 9.11(1) Å and c = 10.86(2) Å (at 100K). The transformation can be ascribed to a rearrangement of the electronic structure of Cs.     

Clusters of sulfur and selenium in nanoporous carbon

The results of x-ray diffraction, x-ray photoelectron spectroscopy, electrical, and galvanomagnetic studies of nanoporous carbon with sulfur and selenium nanoclusters introduced into pores are analyzed. Conclusions are drawn concerning the short-range order in the introduced clusters and their interaction with carbon.     

Electrical resistivity and glassy behaviour in crystalline metallic alloys

Positional disorder due to loss of translational symmetry is suggested as being responsible for most of the concentration dependence of the electrical resistivity of certain disordered transition metal alloys. It is then argued that in such cases the existence of tunneling states should be observable at low temperatures. Measurements of the thermal conductivity on Ti_0.67V_0.33 between 0.06 and 10 K confirm this conjecture.     

Coupled-Hartree-Fock calculations of susceptibilities and magnetic shielding constants

Coupled Hartree-Fock calculations on the susceptibilities X and magnetic shielding constants σ are reported for the title molecules. Very large gaussian basis sets have been used in order to come sufficiently close to the Hartree-Fock limit. The basis set dependence of X and σ is discussed. In addition the applicability of two methods (maximum of X [20] and closure relations [21, 22]) for the prediction of the best gauge origins is investigated.

For C₂H₂, C₂H₄ aand C₂H₆ accurate theoretical results for the complete tensors of X and σ are given for the first time. For ethylene antishielding of σ _yy ^C is observed and illustrated by means of the induced electric currents.     

Very low temperature specific heat of crystalline zirconium in normal and superconducting states

Specific heat measurements of zirconium between 0.03 and 1.2 K in both normal and superconducting states are reported. In the normal state a purely linear electronic contribution is observed down to 0.1 K; at lower temperatures there appears the onset of a nuclear hyperfine contribution which is unobservable in the superconducting state within our experimental time scale.