Observation of Hall Scaling in MgB2 Thin Films

We have measured the Hall resistivity, _xy , and the longitudinal resistivity, _xx , in superconducting MgB₂ thin films in a mixed-state while changing the magnetic field and the current density. A Hall scaling behavior without the anomalous Hall effect was observed with a exponent of 2.0±0.1 in _xy =A _xx . This exponent is observed to be constant, i.e., independent of magnetic field, temperature, and current density.     

Behaviour of amorphous poly(ethylene terephthalate) annealed at T<T g by thermally stimulated currents

Thermally stimulated current (TSC) discharges in open circuit of amorphous poly(ethylene terephthalate) (PET) corona-charged electrets show a heteropolar relaxation at 87 °C, ₁ between and peaks. This relaxation tends to become homopolar when the sample is annealed at temperatures below the glass transition temperature. This is due to the formation of a trapped charge density on the surface of the material that originates, during the TSC discharge, a current that counteracts the one that results in ₁ This trapping effect, which initially is null, increases with annealing due to the rise in resistivity. On the other hand, TSC discharges in short-circuited annealed samples result in a heteropolar peak, ^*, that corresponds to ₁ The area of ^* increases with the annealing time in a bounded way. This peak is related to the formation of thermal nuclei (embryos) in the bulk of the material that act as heterogeneities. This suggests that ₁ is associated with a barrier-type polarization. If the annealed sample is heated to temperatures above the glass transition temperature, the tendency to the inversion of ₁ vanishes and ^* disappears, whereas and are modified. This suggests that relaxation is related to a Maxwell-Wagner-Sillars effect.     

Hall-Effect in LuNi2B2C and YNi2B2C Borocarbides in Normal and Superconducting Mixed States

It was shown that the Hall resistivity _xy for LuNi ₂ B ₂ C and YNi ₂ B ₂ C is negative in the normal and mixed states and has no sign reversal below T _c . In the mixed state the scaling relation _{xy xx} (_xx is the longitudinal resistivity) was found for both compounds with 2.0. In the normal state a distinct nonlinearity in the _xy(H) dependence, accompanied by a large magnetoresistance, was found below 40 K only for LuNi ₂ B ₂ C. The difference in the behaviour of Lu- and Y-based borocarbides seems to be connected with the difference in the Fermi surfaces of these compounds.     

Electron transport properties of deformed potassium and a potassium-rubidium alloy from 0.08 to 4.2 K

Measurements have been performed of electrical resistivity and thermoelectric ratioG on deformed samples of potassium as well as of on a deformed 0.077 at %KRb alloy. A large anomaly in (T) forT<0.5 K is ascribed to electrons interacting with vibrating dislocations and it is shown that the data are consistent with a model of Gantmakher and Kulesko in which the scattering arises from local phonon modes associated with the dislocations. ForT>1 K, an increase in (T) is ascribed to the suppression of phonon drag by the dislocations. The latter is qualitatively confirmed by theG measurements. A maximum inG at 0.5 K is observed when dislocations are present. The two effects in (T) outlined above are so large that the change in the electron-electron scattering contribution to due to deformation cannot be precisely determined.     

Equation of state of3He near its liquid-vapor critical point

We report high-resolution measurements of the pressure coefficient (P/T) for³He in both the one-phase and two-phase regions close to the critical point. These include data on 40 isochores over the intervals–0.1t+0.1 and–0.2+0.2, wheret=(T–T _c )/T _c and =(– _c )/ _c . We have determined the discontinuity (P/T) of (P/T) between the one-phase and the two-phase regions along the coexistence curve as a function of . The asymptotic behavior of (1/) (P/T) versus near the critical point gives a power law with an exponent (+–1)^–1=1.39±0.02 for0.010.2 or–1×10 ^–2t–10 ^–6 , from which we deduce =1.14±0.01, using =0.361 determined from the shape of the coexistence curve. An analysis of the discontinuity (P/T) with a correction-to-scaling term gives =1.17±0.02. The quoted errors are fromstatistics alone. Furthermore, we combine our data with heat capacity results by Brown and Meyer to calculate (/T) _c as a function oft. In the two-phase region the slope (²/T ²)_c is different from that in the one-phase region. These findings are discussed in the light of the predictions from simple scaling and more refined theories and model calculations. For the isochores 0 we form a scaling plot to test whether the data follow simple scaling, which assumes antisymmetry of – ( _c ,t) as a function of on both sides of the critical isochore. We find that indeed this plot shows that the assumption of simple scaling holds reasonably well for our data over the ranget0.1. A fit of our data to the linear model approximation is obtained for0.10 andt0.02, giving a value of =1.16±0.02. Beyond this range, deviations between the fit and the data are greater than the experimental scatter. Finally we discuss the (P/T) data analysis for ⁴ He by Kierstead. A power law plot of (1/) P/T) versus belowT _c leads to =1.13±0.10. An analysis with a correction-to-scaling term gives =1.06±0.02. In contrast to ³ He, the slopes (²/T ²)_c above and belowT _c are only marginally different.Work supported by a grant from the National Science Foundation.     

Relaxations in semicrystalline polyethyleneterephthalate using thermally stimulated currents

Relaxation processes at temperatures above 20 °C in semicrystalline polyethylene-terephthalate have been studied using thermally stimulated depolarization currents (TSDC). The discharge curve shows three relaxation peaks (c, c and *) whose positions and intensities depend on the polarization conditions and the crystallinity. Relaxations c and c are heteropolar, while * may be homopolar or heteropolar according to the polarization temperature used. The effect of the crystallinity on these relaxations has been analysed by the thermal steps stimulation (TSS) method applied to an amorphous sample. Results show that c is fundamentally a dipolar relaxation associated with the amorphous interlamellar zone. The relaxation c is associated with the release of a free charge trapped in the amorphous regions, and * is a Maxwell–Wagner–Sillars relaxation associated with crystalline – amorphous interphases. For polarization temperatures above 150 °C, two relaxations are observed only as a consequence of overlapping C and * relaxations. © 1998 Chapman & Hall     

Temperature dependence of electrical resistivity of deformed and undeformed V-rich V3Si single crystals

The electrical resistivity (T) of V-rich V₃Si single crystals (T _c-11.4 K) was measured from 4.2 to 300 K along the directions of [1 0 0] and [1 1 1] before and after plastic deformation at 1573 K. Anisotropy of (T) was observed although V₃Si has the cubic A15 structure. Plastic deformation does not affect the normal-state (T) behaviour but changes the normal-superconducting transition width T_c. At low temperatures (T _c<T 40 K), (T) varies approximately as T ⁿ where n-2.5 and this behaviour does not contradict the (0)- phase-diagram plot proposed by Gurvitch, where is the electron-phonon coupling constant and (0) is the residual resistivity.     

Velocity of second sound and superfluid density near the superfluid transition in3He-4He mixtures

Using superleak condenser transducers, the velocity of second soundU ₂ has been measured near the superfluid transition temperature T in³He-⁴He mixtures with molar concentrationsX of³He of 0.0, 0.038, 0.122, 0.297, and 0.440. We have obtained the superfluid density _s/ fromU ₂ on the basis of linearized two-fluid hydrodynamics. The results for _s/ are consistent with those obtained from the oscillating disk method, as expected from two-fluid hydrodynamics. The value of _s/ at eachX could be expressed by a single power law, _s/=k, where =1-T/R, with the experimental uncertainty. It is found that the exponent is independent of concentration forX0.44 within the experimental uncertainty. This concentration independence of is in agreement with the universality concept. From the conclusion that the values of are universal forX0.44, the concentration dependence of the superfluid component _s is expressed by an empirical equation _s(X, )=²_s(0, ). It is found that corresponds to the volume fraction of⁴He in the superfluid³He-⁴He mixture. The value of is in agreement with that obtained from the measurement of the molar volume by others.This paper is based on a thesis submitted to Tokyo University of Education in partial fulfillment of the requirements for the Ph.D. degree.     

Varistor characteristics in PTCR-type (Ba,Sr)TiO3 ceramics prepared by single-step firing in air

This paper deals with donor, acceptor-codoped (Ba_0.4Sr_.6)TiO₃ ceramics with distinct varistor characteristics at room temperature, which were prepared by single-step firing in air. The materials, with the Curie point at around –90 °C, exhibited a large PTCR (positive temperature coefficient of resistivity) effect of more than seven orders of magnitude in the temperature range –90 °C (the resistivity 10³ · cm) to room temperature ( > 10¹⁰ · cm). An apparent dielectric constant of >20000 and tan < 0.05 (at 100 kHz) were observed for the present materials at room temperature, and moreover, the materials exhibited nonlinear current-voltage characteristics with the nonlinear coefficient, , in the range 7–12 and the varistor field, E_v, in the range 0.3–1.0 kV/cm. The value of in the present materials increased systematically with increasing in their PTCR temperature range. It has been found that there exists a close correlation between and the grain-boundary potential barrier height, e, obtained from the -T characteristic of the materials. An almost linear relationship was also found to exist between and log E_v for the present materials.     

Temperature-density parameters of Freon-13 on the saturation line

Experimental data of a high degree of accuracy are presented on the temperature-density parameters of Freon-13 on the saturation line in the density range of (0.08246–1.6061)·10 kg/m³.Notation T absolute temperature of phase transition from two-phase to one-phase state (or vice versa) - T_c critical temperature - , densities of liquid and vapor, respectively, on saturation line - _c density at critical points - average density - =(T_c–T)/2 reduced temperature - parameter of order, equal to ' – _c – b for the liquid phase and _c + b – "for the vapor phase Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 830–834, November, 1979.     

Temperature dependence of resistivity for thermally diffused V3Si multilayer films

Results concerning V₃Si films produced by a simple annealed multilayer technique are reported together with X-ray diffraction patterns, Auger spectroscopy, and Rutherford backscattering analysis. Low-temperature electrical resistivity measurements are discussed. It is found that the V₃Si films exhibit aT ² dependence in the temperature rangeT _c T23 K and aT ^2.6 dependence in the rangeT _c T40 K. The normal-state resistivity in the whole temperature range (T _c T600 K) is analyzed in the framework of Cote-Meisel theory. Consistent values of the saturation resistivity _m and of the Debye temperature are obtained by fitting the experimental data with the Cote-Meisel expression for (T).     

Electrical resistivity of nickel-rich nickel-chromium alloys between 4 and 300 K

Electrical resistivity of Ni–Cr alloys containing 5.5, 11.3, 15.7, 16.8, 19.4, 22.0, 24.6, and 27.0 at % Cr has been measured as a function of the absolute temperatureT between 4 and 300 K. The sample with the Cr content of 22.0 at % exhibits a small minimum at about 10 K. No minimum has been observed in any other of the above samples, although an anomalousT dependence has been found in alloys containing 15.7, 16.8, and 19.4 at % Cr. The minimum has been discussed from the viewpoint of the Béal-Monod theory for the Kondo effect in concentrated systems and the mechanism by Greig and Rowlands based on aT-dependent decrease of the impurity electrical resistivity. It is concluded that the minimum in the Ni–Cr system is still a phenomenon which is not well understood at the present time.     

Question of determining the composition of composites by a tomographic method

One possible method of determining the volume content of composite components by using x-ray calculational tomography is examined.Notation , _T, _fi, P_b, _b, _w, _im material densities, theoretical, fiber, binder, pore, water, impregnating fluid - _fi, _b, _p fiber, binder, pore volume contents - f_fi, f_b, f_p, f_di, f_di ^*, f_cij, f_im linear coefficients of attenuation of the fiber, binder, air of the i-th layer of the dry specimen - n quantity of cells in the i-th layer, m_fi, m₁ m₂, weight of the dry and impregnated specimens in air and in water - C_cl closed porosity - S_f rms deviation of the linear attenuation coefficients - volume closed pore content Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 738–745, May, 1989.     

Crossover equation of state of normal hexane in the critical region

The coefficients of the basic crossover equation of state of n-hexane are determined in the critical region from experimental P, , T and C_p, P, T data. In the reduced density and temperature ranges 0.35_c1.65 and 0.982T/T_c1.23 the root mean square errors of the calculated pressure, isobaric heat capacity, and isochoric heat capacity were 0.115%, 4.87%, and 3.04%, respectively.Academician M. D. Millionshchikov Petroleum Institute, Grozny, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 2, pp.185–191, August, 1993.     

Solution of thermal conductivity problems with boundary condition of the third kind and arbitrary coordinate and time dependence of the biot number

An analytical solution of the thermal conductivity problem with boundary conditions of the third kind and arbitrary coordinate and time dependence of the Biot number is found in the form of a converging series of quadratures.Notation , z dimensionless coordinates - dimensionless temperature - Q dimensionless volume heat-liberation density per unit time - Fo=/² Fourier number - Bi₁(, Fo)=(, Fo) · / Biot number - thermal diffusivity coefficient - plate thickness - time - (, Fo) heat-liberation coefficient - thermal conductivity coefficient - i summation index - Jo zero order Bessel function of the first kind Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 536–540, September, 1981.     

Anisotropic Electrical Transport in MgB2 Single Crystals

We report on study of transport properties of MgB₂ single crystals. The normal state resistivity has been found to be anisotropic with resistivity ratio _c / _ab =3.5. In agreement with the results of band structure calculations the normal state Hall effect measurements with H//ab-planes and H//c-axis show two type carrier behavior. Below T _c, the in-plane as well as the out-of-plane Hall resistivity, _xy and _zx , display no sign change anomaly. Furthermore, both _xy and _zx have been found to scale with corresponding longitudinal resistivity with the same exponent =1.5.     

Some transport properties of palladium films

The effect of deposition rate and substrate temperature on the electrical resistivity (), temperature coefficient of resistance (TCR) and thermolelectric power (TEP) of palladium films, in the thickness range 2 to 25 nm, is found to be marked. Higher rates of deposition and substrate temperatures are found to result in larger grains and hence changes in transport properties. The Fuchs-Sondheimer theory is used to explain the size effect in palladium films while the Mayadas-Shatzkes and Meyer relations are employed to study these effects on, TCR and TEP.     

Joule-Thompson effect in a disperse medium

An expression for the Joule-Thompson coefficient of a polydisperse medium subject to throttling is derived in the relaxation approximation of thermodynamics of irreversible processes, with both temperature and velocity relaxation in the phases taken into account.Notation A_qk, A_fk thermal and momentum interphase exchange affinities - _qk, _fk relaxation parameters - T, w temperature and velocity of a phase relaxation in the mixture - density of the mixture - T_o, T_k temperature of the carrier phase and of the k-th group of solid particles - p pressure of the carrier phase - h enthalpy of the mixture - W _o ² /2 specific kinetic energy of the carrier phase - _o, _k volume concentration of the carrier phase and of the k-th group of solid particles - _o, _k true density of the carrier phase and of the k-th group of solid particles - c_v and c_p constant-volume and constant-pressure specific heats of the mixture - c_k specific heat of the k-th group of solid particles - c_v, c_p constant-volume and constant-pressure specific heats, respectively, of the mixture referred to volume - _qk, _fk temperature and velocity relaxation times, respectively, of the k-th group of solid particles - t times - frequency in the Fourier series expansion - differential Joule-Thompson coefficient (adiabatic throttle effect) - N number of groups of particles in the mixture Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 825–829, November, 1979.     

The crystal growth and thermoelectric properties of chromium disilicide

Single crystals of chromium disilicide about 8 mm in diameter and 35 mm long were grown using the floating zone technique. Measurements of electrical resistivity , Hall coefficient R and thermoelectric power were carried out in the temperature range from 85 to 1100 K. The values of and showed the anisotropy over the temperature range studied. The ratios parallel and perpendicular to the c-axis were / =1.9 and /=1.7 respectively, at room temperature. It was found to be a degenerate semiconductor having the hole concentration of 6.3×10²⁰ cm^–3 below 600 K. The effective masses of holes parallel and perpendicular to the c-axis determined from the thermoelectric power and the hole concentration near room temperature were estimated to be five and three times as large as a free electron mass, respectively. The calculation on the values of and was made using those effective masses. These values showed good agreement with the observed values in the temperature range from 150 to 1100 K.