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In the contactless determination of critical current density in a DC or AC magnetization experiment, the use of an appropriate assumption about the field and current distribution in the sample is of key importance. While there exist generally accepted theoretical models describing the flux penetration into some simple shapes such as the slab, strip or disc, the case of composite tape containing many superconducting filaments in a metallic matrix is far from being completely understood. We compare the values of the critical current density obtained from transport measurements and the values evaluated from the AC susceptibility data for two Bi-2223/Ag multifilament tapes of different filament architecture. In one tape the filaments form two columns; in the other they are arranged in an overlapping pattern. The pattern of flux penetration into the two filamentary structures is examined and its consequences for the critical current density evaluation from the AC susceptibility measured in the perpendicular geometry are presented. As a result, the typical dimension to consider in the critical state induced by external magnetic field is the thickness of the column of filaments in the case of the columnar tape, and the thickness of an individual filament in the case of the tape with overlapping filaments.

High-resolution measurements have been made of the low-temperature (1 to 9 K) electrical resistivity of Ag following successive stages of cold work. Above about 3 K the effects of cold work depend upon whether the sample has had a chance to recover; this behaviour is consistent with the idea that recovery involves the relaxation of the long-range strain fields associated with dislocations. At lower temperatures cold work appears to enhance the temperature dependence of the resistivity, irrespective of recovery; this dependence is approximately quadratic in temperature with coefficient ∼1 × 10-13 Ω cm K-2, and may be associated with electron-electron scattering. Cold work without recovery seems to increase the incremental resistivity (ρT - ρ0) in Ag above about 5 K, in sharp contrast to the behaviour of Al, and in a manner that is difficult to understand on the basis of any model involving anisotropy of scattering. After recovery (ρT - ρ0) behaves much like that in an alloy of similar residual resistivity.

Results of the first ultra-high-resolution studies of the low-temperature electrical resistivity of thin metal foils are reported. 10 and 25 μm thickness high-purity foils of Ag and Au, and a single 25 μm foil of Cu have been measured over the temperature range 1·2 to 8 K. In all the foils, surface scattering was the dominant resistive mechanism. For all three metals the temperature dependence of the resistivity in the foils appears to be almost the same as that of bulk material having the same residual resistivity. Thus there is no evidence of an additional temperature dependence arising solely from the presence of the surface.

Microstructures of c-axis oriented YBCO thin films made by high-pressure d.c. sputtering on LaAlO3and MgO substrates were examined by TEM. The a-axis oriented grains, second phases and micro-twins were frequently observed in the film. The a-axis oriented grains expanded along their c-axis directions during film growth. The a- and b-axis misorientations were observed in the film on MgO due to serious lattice mis-match between YBCO and MgO. The second phases were often accompanied with a-axis oriented grains suggesting they act as nuclei. These observed results were correlated with the measured Tcand Jcof the films.

Detailed measurements have been made, for the first time, of the refractive index, n, of molten sulphur at temperatures up to 200°C. The melt is highly dispersive; at 120°C n varies between 1·94 and 1·86 over the wavelength range 0·6 to 1·8 μm, The data have been analysed to obtain information on the electronic structure of molten sulphur. The effect of melting is small. Below 159°C, S8 rings are the stable species; above that temperature they polymerize into long chains. The reported measurements suggest that the chains are about 6% more polarizable than the rings, and have an average valence-to-conduction-band gap that is about 1 eV less. Measurements of the absorption coefficient show no anomaly associated with the ring-to-chain polymerization.

Current-voltage characteristics of high-critical-current Bi2Sr2CaCu2O10/Ag ribbons were measured using both transport and magnetization techniques. The slope of these curves changes with magnetic field and temperature in a way very similar to the observedjc(H, T) behavior. This correspondence between the critical current and the slope of theI–V characteristics can be explained within the thermally activated flux creep framework. The dependence ofjc on the angle between field and ribbon is compared to the existing intrinsic anisotropy models.

The thermopower of polyerystalline Pb has been measured from 4·2 to 30 K in magnetic fields up to 48 kG. The magneto-thermopower peaks at about 8 K, the maximum showing a displacement toward higher temperatures as the field increases; at lower temperatures, the field dependence of the thermopower tends to saturate. This behaviour is similar to that for uncompensated metals; any successful theory must therefore predict similar results for compensated and uncompensated metals.

It has been shown, that different starting materials result in Tl-Ca-Ba-Cu-O superconductors of different type even at the same heat treatment process. This manifests itself in the developing structure, in the number, share-rate and superconducting properties of the occurring phases as well. Microcrystals, phase-compositions, crystallinities, unit cells, onset and critical temperatures, magnetic flux exclusions, critical currents, magnetizations and critical magnetic fields essentially unlike from each other have been observed, depending on the starting materials. The presence of a starting compound having low melting point, as Ba(NO3)2 can cause a more compact, better superconducting final product, implying better connection between the grains.

The refractive indices and absorption edges of liquid bromine and iodine have been measured over the temperature ranges 19 to 57°C and 114 to 181°C respectively, and at wavelengths from the absorption edge (700 nm in bromine and 1100 nm in iodine) up to 1800 nm. At 1800 nm the indices are 1.604 in bromine at 19°C, and 1·934 in iodine at 114°C; both liquids are strongly dispersive. The temperature dependence of the refractive index appears to result largely from the thermal expansion of the liquids, and is fairly well accounted for by the Lorenz-Lorentz equation. The absorption edges in both liquids show well-defined exponential regions; neither the positions nor the slopes of the edges depend strongly on temperature. The optical properties of liquid bromine show little evidence of molecular interactions; in liquid iodine they are significant but not dominant. The experimental data on molecular electronic polarizabilities are in good agreement with calculated values.

It was found from plan-view transmission electron microscopy (TEM) observations that c-oriented YBa2Cu3O7−δ(YBCO) films on LaAlO3, prepared by the magnetron sputtering technique had a single crystalline-like YBCO matrix, but always contained some precipitates of impurity phases. A large number of highly defective twin boundaries were also observed in all of these epitaxial films. Such highly defective twin boundaries are thought to be flux pinning centres and also paths for the diffusion of water into YBCO films. Therefore the films need to be passivated against attack from humid air.

An attempt has been made, using high-purity single crystals of tin at 1-2°K, to reproduce the paramagnetic resonance (p.m.r.) reported by Khaikin (1960). No such signal could be found in the range of g-factors between 1.75 and 2.40, and an alternative explanation of Khaikin's observation is suggested. The absence of a p.m.r. signal can be accounted for by either spin relaxation at the specimen surface, or anisotropy of the g-factor over the Fermi surface. Both hypotheses suggest that the g-shift in tin is at least 10%, which is consistent with a theoretical estimate of this quantity.