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The upper critical field H-c2 of alpha-Ti1-xAlx(0 less than or equal to x less than or equal to 0.1) alloys has been investigated in detail. The behaviors can well be described by the theory of type-II superconductors. The electronic specific heat deduced from the superconducting properties is in excellent agreement with previous calorimetric measurements. However, the Fermi velocity obtained here is substantially lower than predicted by band calculation. The present work gives clear evidence that pure Ti is an intrinsic type-II superconducting element due to its very low renormalized Fermi velocity.

Tunneling spectroscopy of Al73Ni17Co10 decagonal single quasicrystals has been measured at ultralow temperatures. In addition to the wide pseudogap observed in previous photoemission experiments. very rich fine structures in the density of states around the Fermi energy were discovered. The fine structures strongly depend on the applied magnetic field and disappear above similar to 4 T. The zero-bias resistance of the junction varies with magnetic fields in a complicated way, which is suggested to be related to the hierarchy structure of quasicrystals. A puzzling hysteretic phenomenon was observed in some bias ranges in zero magnetic field, the origin of which needs to be clarified in the future. [S0031-9007(99)08419-7].

The charge density wave gaps of NbSe 3 have been carefully determinated by tunneling spectroscopy. In contrast to earlier work, the gap parameter associated with the 59 K transition obtained in the present measurements is very close to the mean field value. The gap structures for both the 145 K and 59 K transitions are found to be essentially independent of the applied magnetic field H. The present findings strongly suggest that the anomalous magnetotransport properties of the material originate from some other mechanism than a H-induced improvement of Fermi surface nesting.

High Tc superconducting YBCO films have been fabricated by in-situ pulsed laser ablation method. The substrates used were SiTiO3 (100) and were heated to 650°C during deposition. X-ray diffraction results indicate that the asdeposited films are highly oriented with c-axis perpendicular to the film surfaces. The critical currents were measured at 77.5 K under different magnetic fields from 0 up to 7 T by using dc four point method. The zero resistance temperature was 89 K and the highest critical current density was 2.5 × 106 A/cm2 at 77.5 K under zero field.

The superconducting transition temperature Tc of α TiAl alloys has been measured up to 10 atomic percentage of Al. Tc monotonously increases with a tendency to saturation for high Al content.

The current-voltage characteristics in different magnetic fields are measured on a whisker (2 mm x 0.037 mm x 0.007 mm) of highly anisotropic material Bi2212 with field H parallel to c-axis and H parallel to b-axis, respectively. When H parallel to c-axis, the j(c) versus T relation remains normal for all fields. However, when the field H is along the b-axis, we obtained an abnormal j(c) versus T relation with a peak value appearing at T = 25 K in H = 4 T. The possible explanations are discussed. (C) 2000 Elsevier Science B.V. Ail rights reserved.

Superconducting Y—Ba—Cu—O bulk materials were fabricated by melt—textured growth (MTG) method, where cooling slowly under temperature gradient produces an aligned structure exhibiting high Jc value. The critical current density was measured by continuous dc four—probe method with criterion of 1μV/cm. Jc value has reached 23, 800 A/cm 2 at 77K under 2T magnetic field perpendicular to the current. The magnetic field dependences of Jc from 1 to 7 Tesla show the anisotropy for two orientations (H┴I, H┴a—b plane and H┴I, H//a—b plane). The X—ray diffraction patterns show the crystals preferentially aligned. The SEM and TEM observations of the MTG sample reveal that the sample has dense layered—structure with regular alignment of plate—shaped crystals. Twinning planes of fairly high density exist. A great quantity of dislocations, dislocation loops and stacking faults exist around 211 phase. These crystal defects may be main flux pinning centers. We have measured the zero—field cooled (ZFC) and the field cooled (FC) magnetizations as functions of temperature at various external dc magnetic field. The dependence of irreversibility point T * on 2/3 power of field H for MTG sample was demonstrated. The flux jumping was found in the hysteresis loop below 10K.

YBaCuO, EuBaCuO and TlBaCaCuO superconductors have been prepared by solid-state reaction. The superconducting transition of the samples was measured by the four-point and mutual inductance methods. The zero-resistance temperature and onset of diamagnetism of the best TlBaCaCuO sample have reached 120 K and 117 K respectively. Their critical currents have been measured at zero and different magnetic fields in a temperature range of 63.5 K to 78 K. The highest Jc for a TlBaCaCuO sample in zero field at 78 K reached 1630 A cm-2. In low fields, their critical current density decreases sharply when the magnetic field is increased. The results show that superconducting weak links exist among superconducting grains in all the samples. But in higher magnetic fields, their critical current density slowly decreases with increasing field; this behaviour is roughly similar to that of the Nb3Sn superconducting material. The results of the measurement of lc at different temperatures shows that the lc is proportional to (Tc-T).

The pressure dependence of the superconducting transition temperature, T c , has been studied up to 17 kbar ∗ for a stable sample of an SrLaCuO compound. The onset temperature of transition increased from 37.0 to 45.0 K (at 14 kbar). High T c superconductivity of the sample disappeared below 17 kbar.

High-Tc Tl-Ba-Ca-Cu oxide superconductors with Jc up to 1600 A cm-2 at 77 K have been synthesised. The microstructure and local micro-region composition of the materials were investigated.