Intergranular Critical Current Density in Polycrystalline (Bi-Pb)-2223 High Temperature Superconductor by ac Susceptibility Measurements

The field dependence of real () and imaginary () component of ac susceptibility of superconductors within the critical state model can conveniently be used for evaluating the critical current when field amplitude is larger than the penetration field. A method to analyze the real () and imaginary () component of fundamental ac susceptibility with the objective of extracting the temperature dependence of critical current density J _c(T) is reported. The procedure makes use of the ac susceptibility data of two polycrystalline (Bi-Pb)-2223 samples measured with different excitation amplitudes below and close to the critical temperature. The temperature dependence of J _c is extracted using the isothermal scan over and data. Results obtained from this procedure are found to be in fair agreement with J _c(T) calculated from traditional loss-maximum data.     

Thermal Expansion and Isothermal Compressibility of TlIn1 – xNdxSe2 (0 ≤ x≤ 0.08) Crystals

The thermal expansion coefficient () and isothermal compressibility ( _T ) of TlIn_{1 – x} Nd _x Se₂(0 x 0.08) crystals were measured between 77 and 400 K. In the range 77–160 K, both and _T increase with temperature, the increase in being much steeper. At higher temperatures, and _T change very little. The observed composition dependences of and _T are interpreted in terms of energy-band structure.     

Morphology, crystallography and defects of the intermetallic χ-phase precipitated in a duplex (δ + γ) stainless steel

The ferritic matrix in the Fe-22Cr-5Ni-3Mo-0.03C ferritic-austenic duplex stainless steel undergoes a variety of decomposition processes when aged in the temperature range 650–750°C. These processes involve the precipitation of the austenite and of the and Frank-Kasper phases. The intermetallic -phase is found at both the grains boundaries (homo and heterophase interfaces) and inside the ferritic grains where it adopts an unexpected hexagonal shape. At the early stage of its precipitation, it nucleates at the / and /heterophase interfaces and then grows by expanding exclusively in the ferritic matrix. This study is basically focused on this intermetallic -phase. The crystal structure and the chemical composition are respectively studied by electron diffraction and energy dispersive X-ray spectroscopy. The -phase exhibits rational orientation relationships with the austenite and the -phase with which it is in contact and an invariably cube-on-cube orientation relationship with the ferritic matrix into which it grows. Based on the orientation relationship, the morphology and the number of variants of this -phase are understood in terms of the group theory. The planar defects present in a large density in the -phase, are roughly parallel to {0 1 1}//{0 1 1}. The fault vectors are determined as: 110 and 111, the latter corresponding for a bcc structure to a phase shift, the defects can be simply described as boundaries. Based on the obtained results, a structural proximity between the -phase and a super-cell derived from the ferritic matrix has been brought to light. This super-cell is described as a stacking of corrugated and planar layers obeying the following parallelism {0 1 1}//{0 1 1}. Indeed this super-cell approach provides an interpretation for several microstructural features such as the / interface plane, the planar defects in the -phase and their related fault vectors.It has been also stated that Mo is an efficient -phase forming element. Upon these considerations a detailed characterization provided valuable insights into the precipitation mechanism associated with the -phase formation.     

Effect of composition on the transformation behaviour of duplex 316 weld metal

Several 316 manual metal arc weld metals produced with commercial and experimental consumables were aged between 600 and 850 °C. This resulted in the dissolution of the -ferrite with the appearance of new austenite, M₂₃C₆, intermetallics , and phase. During transformation, the -ferrite becomes progressively enriched in Cr, Mo and Si and, depending on the local composition of the -ferrite, eventually transforms to intermetallic or phases. A transformation model has been developed which indicates that solute diffusion via the / interface is the controlling mechanism. This enrichment process has been found to be important in controlling the formation of intermetallics. In the weld metals containing controlled residual additions of Ti and Ti + B, ageing resulted in the a fine dispersion of MX phase in the austenitic matrix.     

Correlation of burst pressure of GRP cylinders with the stress wave factor

Glass fibre-reinforced plastic (GRP) cylinders are increasingly used for highly stressed structural elements. The higher the demands on the materials, the higher are the fault detection requirements to be met by non-destructive materials testing methods. Acousto-ultrasonics is a valuable aid for the non-destructive evaluation of GRP composite materials, because it may be the answer to evaluating effects of subtle defects in composites. The aim of the research is to evaluate the burst pressure of GRP cylinders by acousto-ultrasonics techniques. The theoretical results have been found to be in good agreement with the experimental values. Hence the results strongly suggest that stress wave factor measurements can be exploited successfully to predict burst pressure of GRP cylinders.Nomenclature P Internal pressure, kgf cm^–2 - d Internal diameter, cm - t Thickness of cylinder, cm - (N ,N ,N ) Resultant forces, kgf - (M ,M ,M ) Moments, kg cm - [A] Extensional stiffness matrix - [B] Bending stretching coupling matrix - [D] Flexural stiffness matrix - ( ⁰ , ⁰ , ⁰ ) Midplane strains - (k ,k ,k ) Curvatures - n Number of laminae - Z Distance from midplane, cm - _u Ultimate tensile strength of GRP composite, kg cm^–2 - S _W Stress wave factor - m Material parameter - Filament winding angle     

Magnetic properties of highly dilutedPdFex andPtFex-alloys. Part II. Susceptibility at micro- and milli-kelvin temperatures

We have measured the 16 Hz susceptibility of the giant magnetic moments induced by Fe impurities in highly dilutedPdFe_x andPtFe_x samples with 2.5 ppm x 75 ppm in a wide temperature range, 30 K T 300 mK, and at static magnetic fields 0,01 mT B 25 mT. We find spin glass freezing at Tf(X)/X0,19mK/ppm Fe forPdFe_x and the larger value 0.26 mK/ppm Fe forPtFe_x. This is the first observation of spin glass freezing inPtFe_x. In the low-temperature range T 0.5T_f(x), the susceptibilities follow — ₀ T with small zero-temperature ₀ values forPdFe_X and vanishing ₀ values forPtFe_x. In the paramagnetic high-temperature range, we find (T — )^it-1 at T 10 mK independent of x forPdFe_x, and at T 2Tf(x) dependent of x forPtFe_x with vanishing values for both systems. The data compare well to the predictions of the Thouless-Anderson-Palmer TAP approach of the Sherrington-Kirkpatrick SK model for spin glasses.     

Hierarchical three dimensional curved beam element based on p-version

This paper presents a three node curved three dimensional beam element for linear static analysis where the element displacement approximation in the axial () and transverse directions ( and ) can be of arbitrary polynomial orders p , p and p . This is accomplished by, first constructing one dimensional hierarchical approximation functions and the corresponding nodal variable operators in , and directions using Lagrange interpolating polynomials and then taking the products (also called tensor product) of these hierarchical one dimensional approximation functions and the corresponding nodal variable operators. The resulting approximation functions and the corresponding nodal variables for the three dimensional beam element were hierarchical. The formulation guarantees C ⁰ continuity. The element properties are established using the principle of virtual work. In formulating the properties of the element all six components of the stress and strain tensor are ratained. The geometry of the beam element is defined by the coordinates of the nodes located at the axis of the beam and node point vectors representing the nodal cross-sections. The results obtained from the present formulation are compared with analytical solutions (when available) and the h-models using isoparametric three dimensional solid elements. The formulation is equally effective for very slender as well as deep beams since no assumptions are made regarding such conditions during the formulation.     

Nonlinear Response of a Continuous Wave NMR Spectrometer for Samples with a Large Magnetization

We present a new insight in the response of a CW NMR spectrometer for highly magnetized samples above 100 MHz. The spectrometer is a bridge made of a magic T. The output of the bridge is proportional to the reflection coefficient, , of a resonant circuit, which is built with a coil containing the sample. The sensitivity of the reflection coefficient to the complex susceptibility of the sample, () = () – j(), depends on the quality factor, Q, of the circuit and filling factor, . When the condition Q 1 is not fulfilled, we show indeed that the use of a simple crystal detector, which is only sensitive to || gives rise to a strong nonlinear response of the spectrometer. Measurements of the complex value of by means of phase sensitive detection allow to recover a linear behavior. We discuss and illustrate those issues with a few circuits we designed for our measurements on liquid ³ He with spin polarizations up to 15 %. A method is described to build in a reproducible and predictable way resonant circuits matched to 50 in the frequency range 100 – 400 MHz with a quality factor as high as 1000 at 4 K.     

Paramagnetic resonance in a “dirty” spin-glass

For a spin-glass with nonmagnetic defects (n _m ^1/3l 1, where n _m is the magnetic impurity concentration and l is the mean free path) an absorption function () is derived. Three ranges of temperature and external magnetic field are considered. In the vicinity of the transition the value of () d is estimated as a function of temperature and field.     

Does Vortex Lattice of YBa2Cu3O6.94 in H⊥c Melt Below Intrinsic-Pinning Irreversibility Line?

Vortex lattice melting in the Hc configuration of an YBa ₂ Cu ₃ O _6.94 single crystal has been investigated by means of the ac susceptibility – i and the magnetic torque . The melting transition of vortex lattice occurs in Hc, too. Since the torque curve shows a sharp peak in the irreversible torque at _c 90° due to intrinsic pinning at lower temperatures, we can determine the irreversibility line for the intrinsic pinning. The melting transition in the Hc configuration appears at temperatures where the intrinsic-pinning peak is absent. We consider that the intrinsic pinning does not affect the nature of the vortex melting transition in the Hc configuration.     

Environmental stress cracking of glassy polymers and solubility parameters

The use of solubility parameters to predict critical stress ( _c ^* ) or strains (_c) for environmental cracking/crazing in several glassy polymers (e.g. PMMA, PPO, PS, PVC, PSF and PC) is re-examined. It is shown that the enthalpic component ( _H ) of the Flory-Huggins semi-interaction parameter () does not always give a good correlation between _c and _H even though solvent molar volume and polymer-solvent molecular interactions have already been considered. Re-analysis of available experimental data using Gent's theory shows that there is a general trend for _c ^* (or _c) to increase with . These results, therefore, support Gent's proposed mechanism of environmental stress crazing/cracking. It is finally concluded that unless a definite relationship can be established between _c or _c ^* with _H it is not possible to predicta priori _c or _c ^* , given the empirical solubility parameters of a solvent. Unfortunately, there are not many such relationships as discovered in this paper.     

Effect of the weight of the admixture on the turbulence structure of a two-phase jet

The effect of gravity on the turbulence structure of an inclined two-phase jet is evaluated according to the Prandtl theory of mixing length.Notation C_x drag coefficient for a particle - D_p particle diameter - g_i components of the acceleration g due to gravity acting on a particle in the direction of jet flow (g_i=g sin ) and in the direction normal to it (g_i=g cos ) - V_poi ^±, V_goi ^± fluctuation components of the velocities of the particles and gas, respectively, at the end of a mole formation - V_fi free-fall velocity of a particle - l _u mixing length - m_p particle mass - t _p length of time of particle-mole interaction - V_pi ^±, V_gi ^± positive and negative fluctuation velocities of particles and of the gas respectively, with the components u_p ^±, u_g ^±, v_p ^±, v_g ^±, k=V_goi/V_fi - V_i ^± relative velocity of the gas - jet inclination angle relative to the earth's surface - empirical constant - _u, jet boundaries in terms of velocity and concentration - _u=y/ _u dimensionless velocity ordinate - =y/ dimensionless concentration ordinate - admixture concentration - u_m, _m velocity and the concentration of the admixture at the jet axis - _g dynamic viscosity of the gas - _s, _g densities of the particle material and of the gas - _g, _p shearing stresses in the gas and in the gas of particles - _m, ₀ shearing stresses in the mixture and in pure gas, respectively Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 3, pp. 422–426, March, 1981.     

Density of States in Superconductor-Normal Metal-Superconductor Junctions

We consider the ₀ -dependence of the density of states inside the normal metal of a superconductor-normal metal-superconductor (SNS) junction. Here ₀ is the phase difference of two superconductors of the junction. It is shown that in the absence of electron-electron interaction the energy dependence of the density of states has a gap which decreases as ₀ increases and closes at ₀ = . Both the analytical expressions for the ₀ -dependence of the density of states and the results of numerical simulations are presented.     

Pair-field susceptibility of superconducting Al-Er films

Measurements of the imaginary part of the pair-field susceptibility have been carried out on dirty-limit superconducting Al films doped with Er impurities at temperatures within 20% of the critical temperature T _c. These studies are the first measurements of (, k) as a function of the pair-breaking parameter . Samples exhibiting values of up to 0.1 were studied. At temperatures above T _c the diffusive time-dependent Ginzburg-Landau equation for order-parameter fluctuations was found to be valid in the presence of pair-breaking, with the Ginzburg-Landau time an increasing function of the pair-breaking, in quantitative agreement with theory. The characteristic frequencies of the transverse and longitudinal modes of the order parameter disequilibrium were determined from the measurements of (, k) below T _c by fitting to a functional form which exhibits the essential features of the most detailed theories, in particular those of Orbach and Entin-Wohlman, Dinter, and Schön and Ambegaokar, The propagating charge-imbalance wave was found to be overdamped for large values of , consistent with the theory of the transverse mode in the presence of finite pair-breaking. The peak in the excess current found near the gap voltage appears to be due to a resonance in the longitudinal mode pair-field susceptibility and not the result of single-particle tunneling as previously suggested by imanek and Hayward. The width of this resonance as derived by Schön and Ambegaokar for the gap regime is equal to the reciprocal of the spin-flip scattering time. The other characteristic feature of the pair-field susceptibility is the peak associated with the longitudinal mode, which occurs at a frequency which is a measure of the relaxation of the amplitude of the order parameter. Dinter's theory, in particular, describes the dependence of the width of this peak on the pair-breaking parameter .Support for this research was initially provided by the Department of Energy and later by the NSF under Grant DMR-8006959. The Office of Naval Research provided He gas used in these experiments.     

New Universal Relations for Liquid-Vapor Phase Equilibrium

Universal relations between the saturation pressure p _LV and the value of =h _LV/ _LV–p _LV, where h _LV .is the latent heat of evaporation and _LV is the volume change of the vapor-liquid transition, and the product of the orthobaric densities _L and _V of the liquid and vapor at coexistence have been discovered. In the temperature range from the triple point to T/T _c0.9, these relations obey a power law with universal exponents. At temperatures 0.9<T/T _c1, p _LV and depend linearly on ln( _{L V}) with retention of universality for substances of different nature.     

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.     

Interplay of Nuclear Magnetism and Superconductivity

The ratio of nuclear saturation magnetization and superconducting critical field, ₀ M _sat / B _S0*, classifies the strength of mutual influence of nuclear magnetism and superconductivity. In order to investigate the interplay of both phenomena for the three distinct cases 1, 1, and 1 we have measured the ac susceptibility of Al, of the intermetallic compound AuIn ₂ , and of the metal hydride TiH _2.07 at ultralow temperatures, 17 K T 1 K, as function of static field 0 B 15 mT. For Al, the interplay enables an absolute measurement of the nuclear magnetization. For AuIn ₂ , we get a steep decrease of B _S (T) and a broadening of the superconducting transition in its nuclear ferromagnetic phase. Surprisingly, the nuclear ferromagnetic state coexists with type-I superconductivity in AuIn ₂. The metal hydride TiH _2.07 , which is under present investigation, is a good candidate to show reentrant superconductivity.     

Critical review of the thermodynamics of the Na-Al-O system

The free energies of formation of various phases in the Na-Al-O systems are critically reviewed for the composition range between pure alumina and sodium-aluminate. The results clearly indicate that in the temperature range between 600 and 1100 K neither-alumina nor'-alumina (Na₂O.5Al₂O₃) are stable with respect to sodium; the most stable phase in that range being sodium aluminate. Least square fitting and statistical analysis of all the available data on the free energy of formation of-alumina deemed accurate yields G _form ⁰ (from oxides) = –8772+1.53T (J/mole of O) (600 T 1200K) If the composition of-alumina is assumed to be Na₂0.11Al₂O₃ then G _form ⁰ (Na_1/17Al_11/17O, from elements) = –565100+109.6T (J mole of O) (600 T 1200 K) If the composition is assumed to be 19 then: G _form ⁰ (Na_1/14Al_9/14O, from elements) = –564000+109.6T (J/mole of O) (600 T 1200K) Based on the only study to date, the best estimate for the free energy of formation of-alumina is G _form ⁰ (Na_1/8Al_5/8O, from the elements) = –567860+114T (J/mole of O) (600 T 1200 K)The uncertainty (95% confidence band) is estimated to be about ±200 J/mole of O. Based on these results-alumina should be thermodynamically stable at lower temperatures, but become unstable at temperatures >900 K and should, kinetics permitting, dissociate into-alumina and sodium aluminate. Experimental evidence, however exists that conclusively shows that-alumina is thermodynamically stable at much higher temperatures than 900 K which leads to the conclusion that G °_form for-alumina reported to date is too high and should be more negative.     

Fabrication and Properties of Semiconducting Barium Lead Titanate Ceramics Containing Low-Melting Glass Additions

The structural parameters of yttrium-doped (Ba,Pb)TiO₃ solid solutions containing low-melting B₂O₃–PbO–SiO₂ (BPS) glass additions were determined by Rietveld powder-diffraction analysis. It is shown that the introduction of BPS enables dense, semiconducting ceramics containing up to 60 mol % PbTiO₃ to be produced by solid-state reactions followed by sintering at markedly reduced temperatures. Increasing the Pb content increases the lattice strain in the solid solutions, while BPS additions have the opposite effect. Sintering of BPS-containing materials leads to the formation of (_{1 – – y} PbY _y )(Ti_{1 –} Pb)O₃ solid solutions on grain surfaces (core–shell structure).     

Effect of Ba and Zn doping in Bi2Pb0.6Sr2Ca2Cu3Oδ superconductors using ac susceptibility measurements

Ac complex susceptibility, = – i, measurements were done on the samples doped with barium and zinc (Bi₂Pb_0.6Sr₂Ca_{2 – x}M_xCu₃O, M = Ba, Zn and x = 0.02 and 0.10). The data of shows that coupling of the grains in Zn-doped samples are weaker than that of Ba-doped samples and hence it could be concluded that Zn-doped samples are dominated by the S-I-S type of weak links, whereas the Ba doped samples are dominated by the S-N-S weak links. Calculated values of I₀ is three times higher in the Ba doped samples such that the values of Josephson coupling energy, E_j is four times that of Zn doped samples. Analysis based on the sensitivity of the data of d(T)/dT versus temperature furnished further information on the two-step transitions related to the coupling of the grains in both systems.