Critical Temperature Ratio Research Articles

Study of superconducting Nb coated 1.5 GHz accelerating cavities

Single cell 1.5 GHz niobium coated accelerating cavities have been developed. Nb film was deposited by cylindrical magnetron sputtering. The film deposited onto the cavities was analyzed by SNMS for depth profile composition and by XRD for microstructure. Critical temperature (Tc) and residual resistance ratio (RRR) of the films were investigated on Al 2O 3 samples, giving (9.25 ± 0.05) K for Tc and 14.5 for RRR. First results of RF measurements on coated cavities showed superficial resistance values in the μΩ range. Possible superficial resistance sources are discussed.

On the surface configuration of solids in relation to the surface free enthalpy excess and its consequences in phase transitions

In previous studies the average number of neighbors (n avrg) of an atom in the surface phase was found to increase by about (5÷20)% between 0 K and the melting temperature for all solid chemical elements in the periodic table. This increment makes the solid surface “geometrically impossible” to exist at the melting temperature. The latter results in the collapse of crystal structure, beginning with the formation of liquid in the surface layers. Ratio of critical and melting temperature is also discussed.

Superconducting state optical conductivity in marginal Fermi liquid model

We have calculated the optical conductivity in the recently introduced phenomenological charge transfer resonance model for the Cu O superconductors. In the pure case, we find that the absorption edge starts as four times the energy gap (Δ o) while it starts at 2Δ o in impure systems because, in the latter case, the momentum can be transferred to the impurities. Also, the structure in the Holstein region is small compared with conventional superconductors with equivalently large values of gap to critical temperature ratio 2Δ o k BT c .

Dependence of the second upper critical field on coupling strength.

We have calculated the second upper critical magnetic field ${\mathit{H}}_{\mathit{c}2}$(T) in the clean and dirty limit for a number of known strong-coupling superconductors based on tunneling-derived kernels. The microscopic theory is used to derive a simple semiphenomenological analytic form for the strong-coupling corrections that involve the single parameter ${\mathit{T}}_{\mathit{c}}$/${\mathrm{\ensuremath{\omega}}}_{\mathit{l}\mathit{n}}$, namely the ratio of critical temperature (${\mathit{T}}_{\mathit{c}}$) to characteristic phonon energy (${\mathrm{\ensuremath{\omega}}}_{\mathit{l}\mathit{n}}$). The parameters in the derived form are fixed through consideration of our numerical data for real materials.

The high residual resistivity of CoSi 2: Evidence for a homogeneity range

In spite of numerous publications dealing with the transport properties of CoSi 2, the very high residual resistivity (about 2 μΩ-cm) of this compound remains to be explained. One possible explanation is the existence of an intrinsic disorder related to some deviation from perfect stoichiometry. To check this hypothesis carefully homogenized bulk samples of different compositions (CoSi 2± x ) have been prepared and characterized. A clear correlation, which provides evidence for a homogeneity range in CoSi 2, between the composition and both the superconducting critical temperature and residual resistivity ratio was found.

Thermodynamic and other properties of a high-Tc excitonic superconductor.

We have calculated the isotope effect, the thermodynamics, and the gap (${\ensuremath{\Delta}}_{0}$) to critical temperature (${T}_{c}$) ratio for an excitonic superconductor. We consider the possibility that some contribution to the pairing interaction is due to the electron-phonon interaction. As the amount of electron-phonon contribution is increased from zero, the thermodynamic ratios start deviating from Bardeen-Cooper-Schrieffer behavior, but in the opposite direction from conventional strong-coupling superconductors. The isotope effect increases very slowly from zero and $\frac{2{\ensuremath{\Delta}}_{0}}{{k}_{B}{T}_{c}}$ remains close to 3.54 for a significant range of phonon coupling strength.

Chiral symmetry breaking with octet and sextet quarks

The finite temperature chiral transition is studied in the quenched approximation for octet and sextet quarks. The ratios of critical temperatures are estimated to be T (8) c/ T (3) c ∼ 7.5 ± 1.5 and T (6) c/ T (3) c ∼ 12.0 ± 2.5.

The plasma dispersion relation near the two–ion hybrid resonance

The dispersion relation of a deuterium –hydrogen plasma is investigated near the ion cyclotron frequency of hydrogen at varying hydrogen temperatures. It is found that at low hydrogen-to-deuterium temperature ratios, only the fast mode and the ion Bernstein mode are coupled around the hybrid layer. Above a certain critical temperature ratio Th< Thc, these two modes become coupled also to a third mode. Around and above Thc, the wave equation is of sixth order rather than of the fourth order previously discussed.

Phase transition in narrow band metals: A model of “superconducting glass”

Abstract Superconducting phase transition in narrow band metal described by Hubbard Hamiltonian with negative U-centers is studied within the mean field approximation. Unlike in the BCS theory of superconductivity, the gap to critical temperature ratio, Δ o /T c , proves to be greater than 2 and is weakly dependent on the occupancy ν (the number of electrons per lattice site). The jump in the specific heat at T c equals ΔC s / C n =5.25/(1+4 ν ) at ν ⪡ 1. Critical temperature diminishes, at even value of ν, which may serve as an explanation of the behavior observed in transition-metal superconductors (Matthias rule).

A comparative study of the thermodynamics of superconducting Nb0.75Zr0.25 and Nb

From the mircoscopic parameters derived from tunneling for Nb/sub 0.75/Zr/sub 0.25/ and Nb we compute and compare their thermodynamic properties using the imaginary frequency axis formulation of Eliashberg theory. While these two materials have similar critical temperatures, Nb/sub 0.75/Zr/sub 0.25/ is found to show much larger strong coupling corrections than does Nb. The substantial increase in the gap to critical temperature ratio observed experimentally can easily be understood by functional derivative techniques.

Preparation of high critical temperature and high resistivity ratio Nb 3Sn films on quartz

Preparation of high critical temperature and high resistivity ratio Nb 3Sn films on quartz

Thermally driven acoustic oscillations, part V: Gas-liquid oscillations

Thermally driven gas oscillations are considered which drive a liquid column at the cold open end. The frequency of the oscillations is lowered by the inertia of the liquid and the Stokes boundary layer is thick. Optimal conditions for thermal driving in the gas occur at correspondingly big tube radii. Experiments conducted inN2 confirm the theoretically calculated stability limits. With hot air driving a water column, a low critical temperature ratio for the oscillations of about 1.5 was observed.

Correlation between critical temperature and other electrical properties for thin tantalum films

Measurements on thin tantalum films prepared by evaporation in ultrahigh vacuum show definite correlation between the critical temperature (Tc) and resistivity ratio (ρ300/ρ10). Empirical relationships are given for films having resistivity ratios in the range 1.2–6 corresponding to a thickness range 11⋅5–965 nm.

Equation for the interfacial tension between demixed polymer solutions

AbstractThe theory of Cahn and Hilliard is used to derive an equation for the interfacial tension (free energy) between some demixed polymer solutions, applying a simple solution model treated by Debye in his theory of light scattering near the critical solution temperature. For a (symmetrical) system containing two polymers in a common solvent it is found that the interfacial tension is given by σ = (l/12½)Ωφp 2σr, where l is the Debye l parameter for the range of molecular interaction—here equal to (2S2)½, where (S2)½ is the radius of gyration of both polymers, Ω is a heat of mixing parameter for polymer‐polymer interaction, φp is the total volume fraction of polymer and σr is a function of the ratio of temperature and critical solution temperature. The equation is in qualitative agreement with experiments of Langhammer and Nestler.

Flux jumping phenomena in sputtered cylindrical niobium films

Measurements of the critical temperature and resistance ratio of cylindrical niobium films, prepared by getter sputtering, indicate that their purity is high. Magnetic measurements on the superconducting films show that flux penetrates to the bore of the cylinder, either in the form of regular jumps or continuously, in a manner resulting in regular hysteresis. The variation of the magnitude of the jumps with applied field and temperature is reported, and the magnitude is also found to be proportional to the square root of film thickness. The latter result is also obtained from a thermodynamic energy balance calculation, but predictions of the flux jump height as a function of the applied field and temperature yield only partial agreement with experiment.

A quartz thermometer: Instrument Practice, 19, No. 10, 907 (1965)

Oil palm boiler clinker (OPB) is a waste byproduct obtained at elevated temperature in an oil palm processing mill. Moreover, in recent years, Concrete filled steel tube (CFST) has been used widely in structures throughout the world. This paper presents an experimental and numerical study on novel sustainable composite beam by using OPB as replacement of natural coarse aggregate in CFSTs. Steel hollow beams (3.2 m length) infilled with natural aggregate concrete and OPB concrete were subjected to flexural load and elevated temperature. The parameters selected for the experimental tests were the cross-section type (square, rectangular) and the infilling type (natural aggregate concrete and OPB concrete). The thermal response, failure modes, critical temperature, temperature distribution in steel tube and infilled concrete, deflection along the span and fire concrete contribution ratio were evaluated. The critical temperature and fire concrete contribution ratio of OPB CFST was found to be higher than natural aggregate CFST, showing superior performance of OPB CFST. Thereafter, simulations were performed and more than 50 models were analyzed to evaluate the effect of yield strength of steel (235–400 MPa), compressive strength of infilled concrete (30–75 MPa), load ratio (0.3–0.6), width-to-depth ratio (2–0.5) and steel ratio (4.4%–2.1%) on the fire resistance time of CFST beam. It was found that the increase in load ratio, steel ratio and yield strength of steel has adverse effected on the fire resistance (FR) time of CFST member. However, the FR time increased significantly with an increase in compressive strength of infilled concrete and cross-sectional dimension of CFST member. Finally, the experimental results were compared with existing equations for CFST columns filled with natural aggregate concrete. It was found that current equations may underestimate the fire resistance of CFST filled with OPB.

Computation of the Critical Flow Function, Pressure Ratio, and Temperature Ratio for Real Air

A method of computing the critical flow function, critical pressure ratio, and critical temperature ratio is presented. Use is made of the NBS Circular 564 tabulated data of the speed of sound, enthalpy, and compressibility. Computations are made for dry real air at stagnation temperature from 60 to 100 F and stagnation pressure from zero to 300 psia. The change in the flow function and ratios is 0.9, 0.5, and 0.4 percent, respectively, over this range. Calculations are also performed at elevated pressure and temperature.

Closure to “Discussion of ‘Computation of the Critical Flow Function, Pressure Ratio, and Temperature Ratio for Real Air’” (1964, ASME J. Basic Eng., 86, pp. 173–174)

Closure to “Discussion of ‘Computation of the Critical Flow Function, Pressure Ratio, and Temperature Ratio for Real Air’” (1964, ASME J. Basic Eng., 86, pp. 173–174)

Solutions of the BCS Integral Equation and Deviations from the Law of Corresponding States

The BCS integral equation has been studied for nonseparable interactions of the Bardeen-Pines form, V(|εε’|). Numerical solutions were obtained using an IBM 7090 for a simple interaction of this form which included the effect of the Coulomb repulsion. The results for the ratio of the energy gap to the critical temperature and for the temperature dependence of the energy gap, the electronic specific heat, and the critical field in terms of the proper reduced quantities were rather insensitive to the form or strength of the interaction. This indicates that the BCS theory gives the law of corresponding states. The calculated ratio of energy gap to critical temperature varies with the ratio of critical temperature to the Debye temperature, and this variation is of the correct order of magnitude if the Coulomb interaction is included. The same model is used to study the isotope effect. With the plausible assumption that the Coulomb cutoff is independent of the ionic mass, there are deviations from the M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−½</sup> law that are larger for small T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> /θ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> superconductors.

On the range of existence of the liquid state

AbstractThe contention sometimes met with that the ratio of critical and triple point temperature is about constant for different substances, is shown to be erroneous. It actually may have values from 1.07 to 12.3. Though some compounds, usually classed as one group, show about the same value for this ratio, other related compounds have largely different values. As a first approximation a linear relation is found between this ratio and the logarithm of the triple point pressure. On the strength of this relation it is suggested that when the vapour pressure of a solid has been measured to about 120 at no reversible melting is to be expected. Reasons are advanced that mercuric sulphide and paracyanogen may be cases in point.