K. Wu

The process of forming 2223 phase from 2212 phase in Bi(Pb)-Sr-Ca-Cu-O System

The process of forming (2223) phase was studied by x-ray diffraction, thermal analysis, as well as electric and magnetic measurements. It was discovered that the formation of (2223) from (2212) is a phase transition-like process. Some possible mechanisms of (2212) to (2223) phase transition-like are discussed. Our results not only explain the difficulty for getting pure (2223) phase sample, but also give a way to prepare high quality (2223) phase sample.

Specific heat studies of high-Tc superconductor YBa2Cu3O7−x

Abstract Specific heat studies of the high-T c superconducting compound YBa 2 Cu 3 O 7− x with bulk transition temperature at 92K are reported. A distinct anomaly of electronic origin in the specific heat is observed with granular-like behavior corresponding to a Sommerfeld constant γ = 7±2mJ(moleCuK 2 ) ±1 Debye temperature ( φo ≈ 400K) is obtained by fitting the experimental data with the theoretical Debye specific heat.

RECTIFICATION PROPERTIES AND INTERFACE STATES OF HETEROJUNCTIONS BETWEEN SOLID C60 AND N-TYPE GAAS

Solid C60/n‐GaAs heterojunctions have been fabricated by deposition of solid C60 film on the (100)‐oriented epitaxial n‐type GaAs substrates and their electrical characteristics have been measured. The rectification ratio is greater than 106 at a bias of ±1 V. The current for a fixed forward bias is an exponential function of reciprocal temperature, from which the effective potential barrier height of the heterojunction is determined to be 0.58 eV. A trap with an energy level 0.35 eV below the conduction band of GaAs at the C60/GaAs interface has been observed by the deep level transient spectroscopy technique.

Superconductivity at 77K in (Pb, Cu)Sr2(Ca, Y)Cu2O7 by post-annealing

Abstract The Pb-based layered copper oxide of (Pb 0.7 Cu 0.3 )Sr 2 (Y 0.6 Ca 0.4 )Cu 2 O z was prepared by solid state reaction. X-ray diffraction analysis showed that the sample had a structure isomorphous to the Tl-1212 phase. By a post-annealing, without any high pressure treatment, the sample showed superconductivity at 77K, which is higher than the reported values to our knowledge. Our experiments not only simplify the process for preparing Pb-based superconductors, but also give a quite new view for this superconductor.

Josephson effects observed in constricted YBaCuO films at liquid nitrogen temperature

Abstract The DC and AC Josephson effects have been observed in constricted superconducting Y-Ba-Cu-O films at liquid nitrogen temperature. The temperature dependence of the critical current was studied. It was found that I c ∝ (T c -T) 3 2 . The induced steps were seen in the I-V characteristics when the sample was irradiated by a microwave field. Separations between steps agrees with the Josephson relation.

STRUCTURE MODIFICATION OF BiSrCaCuO SUPERCONDUCTORS DUE TO Pb-SUBSTITUTION

Pb-substitution to BiSrCaCuO superconductors has modified the crystallographic structure, in addition to the enhancement of the superconducting properties.

Planar organic microcavity of Eu-chelate film with metal mirrors☆

Abstract A new kind of planar organic microcavity consisting of Langmuir-Blodgett (LB) films of rare-earth Eu-chelate Eu(NTA)4HDP sandwiched by silver metal mirrors has been successfully fabricated for the first time by solving the difficulty for preparing of microcavity containing with a sharp luminescence emission medium. The microcavity effects in λ 2 resonant microcavity were demonstrated.

Observation of post-deposition resistance relaxation during growth of semicontinuous metal films

Abstract Semicontinuous niobium and silver films were made in an ultra-high-vacuum (UHV) chamber and in-situ d.c. resistance measurements were performed. After interrupting the deposition, we investigated the immediate ageing phenomenon (relaxation) of the sample resistance on a time scale of about 10 min. Resistance increase and decrease were observed for niobium and silver samples, respectively. The intensity of the relaxation is sensitive to substrate temperature and film thickness. We suggest that edge diffusion and coalescence of islands due to thermomigration of the metal atoms are responsible for the resistance relaxation.

CARRIER CHARACTER OF BI CONTAINING 2223-PHASE DOPED BY MO AND W

Abstract Single-phase samples of the Mo, W doped BiSrCaCuO 2223 phase were synthesized. No impure phases appeared in the X-ray diffraction patterns. The samples, as-prepared and after annealing in O 2 and N 2 atmospheres, were characterized by using thermal analysis, Hall effect and R-T relationship measurement, as well as the X-ray diffraction technique. The experiments showed that there is a close relationship between T c and carrier concentration in these doped samples. To our knowledge, this relationship is obtained for the first time. The effects of Mo and W on the superconductivity were discussed. We suggest that the effect of W and Mo is to change the overall content of oxygen in the samples, hence influencing the superconductivity. The metallic ions in the Bi sites do not directly dominate the superconductivity.

THERMOELECTRIC POWER OF SOME HIGH-TcBi AND Tl COMPOUNDS

Thermoelectric power(S) measurements are reported in several high-Tc Bi and Tl compounds. It is positive and decreases with increasing temperature. In samples which are rich in superconducting phase, an enhancement of S just above Tc was observed. For Bi compounds with two superconducting phases, S(T) measurement has some advantages.