共查询到20条相似文献,搜索用时 31 毫秒
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Between 0.65 K and 3.2 K, the temperature dependence of the vapor pressure P of 3He is defined by the International Temperature Scale of 1990 (ITS-90). However, the ITS-90 vapor pressure equation was not designed to be consistent with the scaling law required for the second temperature derivative of the vapor pressure in the vicinity of the liquid-vapor critical point. In this paper, two scaling-type equations are used to describe the 3He vapor pressure in the region near the critical point. The first scaling equation contains two unknown coefficients which are obtained by taking as reference the temperature $\bar{T}$ at which the product (T c ?T)P presents a maximum ( $\bar{T}=2.56736$ K). The second scaling equation contains three unknown coefficients which are obtained by using as references $\bar{T}$ and T up=3.2 K, the upper value of the ITS-90 interval. In both equations we take for the critical temperature and pressure the values T c =3.31554 K and P c =114?632.7 Pa. The proposed equations, specially the second one, are satisfactorily compared with experimental data for P and dP/dT within the temperature range (T c ?T)/T c ≤0.065 and with semiempirical data for d 2 P/dT 2 within the temperature range 0.0001≤(T c ?T)/T c ≤0.03. 相似文献
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T. F. Smith 《Journal of Low Temperature Physics》1974,17(3-4):323-329
Recent measurements of the elastic constants at temperatures close toT c for niobium and lead would indicate strong individual quadratic strain dependences ?2 T c /?ε i ε j , which combined would predict a considerableP 2 contribution to the pressure dependences of their superconducting transition temperatures. These predictions are in conflict with the direct experimental observations of the variation ofT c with pressure to 25kbar, which exhibit no evidence of any significant quadratic component. The implications of this discrepancy are discussed. 相似文献
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The parameters of liquid-vapor phase transitions p s , ρ s , T s and critical points p c, ρc, T c were determined from the experimental data on the p, ρ, T, x-dependences of aqueous solutions of aliphatic alcohols (methanol, ethanol, n-propanol) that contain 0.2,0.5, and 0.8 mole fractions (x) of ethanol and correspond to single-phase (gas, liquid), two-phase, or subcritical areas. The dependence of the pressure of saturated vapor in solutions on the temperature and density was described by means of the expansion of the compressibility factor Z = p/RTρ m in powers of the density and temperature along the coexistence curve away from the critical point. The temperature dependence of the density of solutions along the coexistence curve and inside the critical area was fitted using the power functions of parameters ω ~ $\tau ^{\beta _i } $ , τ = (T ? T c) and ω = (ρ1,v ? ρc)/ρc. 相似文献
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A. I. Ponomarev V. I. Tsidilkovski K. R. Krylov T. B. Charikova A. A. Lakhtin L. I. Leonyuk 《Journal of Superconductivity and Novel Magnetism》1996,9(1):27-32
The anisotropy of the resistivity and thermoelectric power (TEP)S of Nd1.85Ce0.15CuO4?δ single crystal (T c =17 K) has been investigated. In the temperature rangeT c <T<300 K the ratioρ c/ρab≈104 and the dependencesρ ab (T) andρ c (T) change from quadratic to linear atT~200 K. The dependencesS ab (T) andS c (T) reach a maximum atT>T c and then decrease almost linearly with increasing temperature, changing sign from positive to negative nearT~ 150 K. The features of the resistivity and TEP temperature dependences (the lawρ∝T 2 changing toρ∝T, the change in the sign of S with temperature, and the low TEP anisotropy at largeρ anisotropy) have been interpreted in the framework of the narrow-band model. 相似文献
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W. Herreman 《低温学》1977,17(7):415-418
The reduced viscosity coefficient ηR for the saturated liquid state of argon, neon, krypton, xenon, oxygen, nitrogen, and fluorine is examined as a function of TR and as a function of 1/ρR ? 1/ρoR. The reduction parameters are the critical ones: ηR = η/ηc where ηc is the viscosity of the liquid calculated at the critical point supposing there is no anomalous behaviour; TR = T/Tc, ρR = ρ/ρc and ρoR = ρo/ρc. The density ρo is the density of the liquid where η = ∞.For the inert gases there is a good ηR(TR) correspondence. From this fact the viscosity of radon is calculated.Where ηR is plotted as a function of 1/ρR ? 1/ρoR, a principle of corresponding states is found for the investigated condensed gases. For densities greater than about 2ρc the reduced fluidity φR = 1.868 (1/ρR ? 1/ρoR). In this range the overall average deviation between the calculated and the experimental fluidity is 2.6%. 相似文献
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R. S. Meena Anand Pal K. V. R. Rao Hari Kishan V. P. S. Awana 《Journal of Superconductivity and Novel Magnetism》2014,27(3):687-691
The superconducting and ground state samples of PrFeAsO0.8F0.2 and PrFeAsO have been synthesised via the easy and versatile single step solid state reaction route. X-ray and Reitveld refine parameters of the synthesised samples are in good agreement to the earlier reported value of the structure. The ground state of the pristine compound (PrFeAsO) exhibited a metallic-like step in resistivity below 150 K followed by another step at 12 K. The former is associated with the spin density wave (SDW)-like ordering of Fe spins and later to the anomalous magnetic ordering for Pr moments. Both the resistivity anomalies are absent in case of the superconducting PrFeAsO0.8F0.2 sample. Detailed high field (up to 12 Tesla) electrical and magnetization measurements are carried out for the superconducting PrFeAsO0.8F0.2 sample. The PrFeAsO0.8F0.2 exhibited superconducting onset ( $T_{c}^{\mathrm{onset}}$ ) at around 47 K with T c (ρ=0) at 38 K. Though the $T_{c}^{\mathrm{onset}}$ remains nearly invariant, the T c (ρ=0) is decreased with applied field, and the same is around 23 K under an applied field of 12 Tesla. The upper critical field (H c2) is estimated from the Ginzburg–Landau equation (GL) fitting, which is found to be ~182 Tesla. Critical current density (J c ), being calculated from high field isothermal magnetization (MH) loops with the help of Beans critical state model, is found to be of the order of 103 A/cm2. Summarily, the superconductivity characterization of the single step synthesised PrFeAsO0.8F0.2 superconductor is presented. 相似文献
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A parametric crossover equation of state for pure fluids is adapted to binary mixtures. This equation incorporates scaling laws asymptotically close to the critical point and is transformed into a regular classical expansion far away from the critical point. An isomorphic generalization of the law of corresponding states is applied to the prediction of thermodynamic properties and the phase behavior of binary mixtures over a wide region around the locus of vapor-liquid critical points. A comparison is made with experimental data for pure R32, R 125 and R 134a, and for R32 + R 134a and R 125 + R32 binary mixtures. The equation of state yields a good representation of thermodynamic property data in the range of temperatures 0.8Tc(x) ≤ T ≤ 1.5Tc(x) and densities 0.35 ?c(x) ≤ ? ≤ 1.65?c(x). 相似文献
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Measurements of the critical mass currentJ c through 0.8-µm-diameter channels in the superfluid phases of3He are reported. Experiments were made at pressures from 0 to 27.4 bar in zero external magnetic field. The pressure difference ΔP along the flow channels is immeasurable within our resolution of ±0.1 µbar for sufficiently low currents in both the A and B phases, implying small or zero dissipation. In the B phase ΔP grows rapidly with increasing current aboveJ c. At low pressuresJ c behaves like (1?T/T cyl)3/2, whereT cyl is interpreted as the reduced superfluid transition temperature inside the flow channels;T cyl/T c=0.935 atP=0. If the liquid in the channels is in the A phase, the behavior of ΔP vs. the mass currentJ s depends on the phase A or B outside the channels. During warming a drop of about30% inJ c is found both atT BA(cyl) and at;T BA(cyl) is the reduced B→A transition temperature in the channels. AboveT BA a second dissipation mechanism, with a smallerd(ΔP)/dJ s, is observed at lower currents. These features indicate that in the A phase the ends of the channels have an important effect on the flow. 相似文献
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Safa Mnefgui Abdessalem Dhahri Jemai Dhahri El-Kebir Hlil 《Journal of Superconductivity and Novel Magnetism》2013,26(2):251-260
We have investigated the structural, magnetic, and electrical transport properties of a series of ABO3-type perovskite compounds, La0.67Sr0.33Mn1?x V x O3 (0≤x≤0.15). The samples were characterized by X-ray diffraction and data were analyzed using Rietveld refinement technique, it has been concluded that these materials have the rhombohedral structure with $\mathrm{R}\overline{3}\mathrm{C}$ space group. The magnetization and resistivity measurements versus temperature proved that all our samples exhibit a ferromagnetic to paramagnetic transition and a metallic to semiconductor one when the temperature increases. Both the Curie temperature T C and the resistivity transition temperature T P of the composites decrease, while the resistance increases as the V content increases. It has been concluded that the electrical conduction mechanism in the metallic regime at low temperatures (T<T P) can be explained on the basis of grain boundary effects and the single electron-magnon scattering process. Resistivity data were well fitted with the relation ρ=ρ 0+ρ 2 T 2+ρ 4.5 T 4.5, whereas the adiabatic Small Polaron Hopping (SPH) and Variable Range Hopping (VRH) models are found to fit well in the paramagnetic semiconducting regime at the high temperature (T>T P). 相似文献
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《低温学》1987,27(7):391-395
A thermometer based on the temperature dependence of the negative ion mobility in superfluid 3He is described. The device can be used for monitoring the temperature of an open geometry sample of 3He in the range 0.4 ≲ T/Tc ≤ 1. The ion thermometer is most sensitive immediately below Tc, in the Ginzburg-Landau region; above T ≈ 0.95Tc a resolution of 0.1 μK can be achieved. The measuring technique provides an on-line display of the relative mobility, μ(T)/μ(Tc), and the ions probe the temperature of the 3He sample directly, which leads to a short time constant τ < 10 s. The relative mobility versusT/Tc is insensitive to the external magnetic field and the pressure of the sample. Only a low electric field, E ≲ 10 V cm−1, with essentially no homogeneity requirements is needed. Parasitic heating due to the flow of ions is of the order of 1 pW. 相似文献
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R. F. Bishop 《Journal of Low Temperature Physics》1974,15(5-6):601-635
A fully self-consistent Hartre-Fock theory, using the Coulomb interaction screened by the polarization insertions calculated in the self-consistent random-phase approximation, is applied to thed-dimensional, dense, charged Bose gas at temperatures close to the transition temperatureT c . The quasiparticle energy spectrum is calculated and shown to behave atT c like ε(k)=Ak σ for smallk, and σ is calculated as a function of the dimensionalityd. The change in transition temperature from that of an ideal gas at the same density, and of the chemical potential are shown to be given by (T c ?T c0 )/T c0 ≈Xr s (d?2)/3 and μ c ≈Yr s 2/3 , wherer s is the ratio of the interparticle spacing to the Bohr radius. Approximate expressions are given for the coefficientsX andY. The critical exponents are calculated, and the system is shown to obey exact scaling. 相似文献
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E. Arushanov S. Levcenko G. Fuchs S.-L. Drechsler 《Journal of Superconductivity and Novel Magnetism》2013,26(8):2727-2734
In Li1?x FeAs, Li1?x FeP, and Na111 (Na1?δ FeAs, Na0.9FeAs, NaFe0.95Co0.05As, NaFeAs0.8P0.2) members of the 111-iron-pnictide superconductor family, the temperature dependent resistivity ρ can be scaled into a single curve described by a scaling function. In particular, the ρ(T) dependences can be reproduced by the expressions $\rho(T) = \rho_{0} + cT\exp( - \frac{2\varDelta }{T})$ and $\rho(T) = \rho_{0} + (a/T)\exp( - \frac{2\varDelta }{T}) + bT$ for Li1?x FeP and Li1?x FeAs, Na-111 crystals, respectively. The scaling was performed using the energy scale 2Δ, the parameters a, b, c, and the residual resistivity ρ 0 as scaling parameters. The existence of a single metallic ρ(T) curve is interpreted as an indication of a few mechanisms in various compounds, which dominates the different scattering of charge carriers in 111-iron-pnictide superconductors studied so far. Thus, the scaling of the normal-state properties seems to be a general feature not only for high-T c cuprates, but also for the iron-pnictides superconductor family. 相似文献
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D. A. Kirzhnits E. G. Maksimov D. I. Khomskii 《Journal of Low Temperature Physics》1973,10(1-2):79-93
A critical temperatureT c of a superconducting transition is calculated for a rather general form of the electron-electron interaction. It is shown that even if both the energy and momentum dependence of the interaction is included, the equation determiningT c coincides formally with the corresponding equation of the BCS theory. The kernel of this equation is a smooth real function of its variables; it is expressed through ρ(k, E), the spectral density of the inverse dielectric function of the system. The expression forT c is written in terms of ρ(k, E); this enables us to analyze the dependence of the critical temperature on the properties of the metal in a normal state. Some simple models illustrating the results are considered, and a discussion of the limits onT c is given. 相似文献
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Y.H. Huang 《低温学》2006,46(12):833-839
A saturation vapor pressure equation, p(T), is an essential component in the 3He state equation currently under development. The state equation is valid over the range 0.01-20 K with pressures from 0 to the melting pressure or 15 MPa. The vapor pressure equation consequently must be valid from 0.01 K to the critical temperature. This paper surveys available 3He critical temperature and pressure measurements, leading to new recommended critical values of 3.3157 K and 114603.91 Pa. The ITS-90 temperature scale is defined by the 3He vapor pressure from 0.65 to 3.2 K. A new vapor pressure equation is developed for the interval from the upper end of the T90 scale to this newly defined critical point, employing a mathematical form in which the second derivative d2p/dT2 diverges in agreement with scaling laws at the critical point. Below 0.65 K, an empirical vapor pressure expression is adopted, consistent with a theoretical expression valid in the limit T → 0. These two new components are fitted to be piecewise continuous with the EPT-76 p(T) scale rather than the ITS-90 T(p) scale between 0.65 and 3.2 K. Probable deviations between this vapor pressure scale and PLTS-2000 melting pressure-temperature scale are recognized, but not reconciled. 相似文献
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I. García-Fornaris A. A. Planas P. Muné R. F. Jardim E. Govea-Alcaide 《Journal of Superconductivity and Novel Magnetism》2010,23(8):1511-1516
We have studied the normal and superconducting transport properties of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) ceramic samples. Four samples, from the same batch, were prepared by the solid-state reaction method and pressed uniaxially at different compacting pressures, ranging from 90 to 250 MPa before the last heat treatment. From the temperature dependence of the electrical resistivity, combined with current conduction models for cuprates, we were able to separate contributions arising from both the grain misalignment and microstructural defects. The behavior of the critical current density as a function of temperature at zero applied magnetic field, J c (T), was fitted to the relationship J c (T)∝(1?T/T c ) n , with n≈ 2 in all samples. We have also investigated the behavior of the product J c ρ sr , where ρ sr is the specific resistance of the grain-boundary. The results were interpreted by considering the relation between these parameters and the grain-boundary angle, θ, with increasing the uniaxial compacting pressure. We have found that the above type of mechanical deformation improves the alignment of the grains. Consequently the samples exhibit an enhance in the intergranular properties, resulting in a decrease of the specific resistance of the grain-boundary and an increase in the critical current density. 相似文献