Xie Sishen

Subsolidus phase relations of the Y2O3-SrO-CuO system

The 960 °C subsolidus phase relations of Y2O3-SrO-CuO system have been determined by X-ray diffraction. The section at room temperature in the Y2O3-SrO-CuO ternary system can be divided into six three-phase and two-phase regions. In this system, there are five binary compounds: Y2SrO4, Y2Cu2O5, Sr2CuO3, SrCuO2 and Sr14Cu24O41 as well as a solid solution YxSr14−xCu24O41 (0 <x≤ 4). The structure of the solid solution is discussed. The variation of the lattice parameters of the solid solution with increasing yttrium content has been measured. Electrical resistivity measurements of the solid solution show that there is no superconductive phase in the Y-Sr-Cu-O system.

Phase relations and compounds in the Sm2O3-BaO-CuO system at 950 °C in air

Abstract The subsolidus phase relations of the Sm2O3-BaO-CuO system at 950 °C in air were investigated. The system can be divided into eight three-phase regions and two two-phase regions. There is one ternary compound Sm2BaCuO5, a solid solution Sm1+xBa2−xCu3Oy, and three binary compounds Sm2CuO4, BaCuO2, and Sm2BaO4. Sm2BaO4 was isolated with orthorhombic unit cell, space group Pbna, and lattice constants a = 12.313 A , b = 10.535 A and c = 3.564 A . The solid solution range of Sm1+xBa2−xCu3Oy was determined from x = 0 to 0.4, and a phase transition from orthorhombic to tetragonal symmetry occurs at x = 0.25. With an increase in x, Tc decreases monotonically from 94 K (onset), and the compounds of Sm1+xBa2−xCu3Oy finally become semiconducting.

The role of precursors in making Bi(Pb)-Sr-Ca-Cu-O superconductors

Sr-Ca-Cu-O compounds were used as precursors to prepare Bi system superconductors. When Sr2Ca2Cu3O7 and Sr2Ca2Cu4O8 react with Bi2O3 (PbO) for 30 h, samples of Tc(0) higher than 100 K were obtained. Bi2O3 may have been directly inserted into the layered structures of Sr-Ca-Cu-O compounds and hence Bi-system superconductors formed; the authors found that the existence of Ca7Bi10O22 in the Bi system superconductors reduced Tc(0), and extra CuO assisted the formation of the superconducting phase.

The critical current density Jc(T,H) of high-Tc superconducting oxides

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 preparation, superconductivity and thermal characteristics of the Tl−Ba−Ca−Cu oxide superconductor

The high-Tc Tl-Ba-Ca-Cu oxide superconductor with a critical current density Jc=1630 A cm-2 at 77 K has been prepared and high-Tc properties have been observed in this system. The zero-resistance transition temperatures T(c0)=120.3 K and Tc(AC chi )=119 K were observed by resistance and magnetic susceptibility measurements, respectively. The stability and reproduction of the materials are absolutely necessary. Thermal characteristics were investigated.

Study of C70 Adsorbed on Silver Surface by Surface Enhanced Raman Scattering

Twelve new features from our Raman measurements of C70 have been observed by using the silver surface enhanced Raman scattering substrate with very high enhanced factor and highly sensitive Raman set. The results and discussion in this letter would make new knowledge to vibration modes of C70. The experimental data of the study confirm the validity of Jishis calculation with a small error.

Fabrication of Intrinsic Josephson Junctions on Bi2Sr2CaCu2O8+? Single Crystals with Reproducible Surface Junctions

Intrinsic Josephson junctions on Bi2Sr2CaCu2O8+δ single crystals are successfully fabricated using photolithography and Ar ion milling. Here we discuss the properties of the surface CuO2/metal bilayers and surface junctions prepared with different crystal cleavage conditions and metal film deposition techniques. We show that, by cleaving the crystal at liquid nitrogen temperature in vacuum, the contents of the (interstitial) oxygen in the Bi-O layers become stable upon cleavage, leading to a CuO2/metal bilayer and to surface junctions with reproducible properties. These results can be useful for practical device fabrications as well as for the studies of the contact properties between high Tc superconductors and normal metals.

A high-Tc superconducting phase in the Ba-Y-Cu-O system

The crystal structure of high-Tc superconductors in the Ba-Y-Cu-O system has been investigated by means of X-ray powder diffraction and electron microscopy. The results indicate that the superstructure based on the distorted cubic perovskite subcell is responsible for the high-Tc superconducting transition at about 90 K. The high-Tc superconducting phase is pseudo-tetragonal with triple periods (3ap) along the (001) direction. The different diamagnetic and resistance behaviour is connected with different proportions of this phase in the samples.

Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2

We have performed low temperature resistivity ?(T) and specific heat C(T) measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is ~ 4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat ?n = 4.51 mJmol?1K2 and the Debye temperature ?D = 419K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/?nTc = 2.84exp(-1.21Tc/T). This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.

Core-Shell Structure and Photoluminescence of CdS Quantum Dots

A double-potential-well model is proposed to describe the core-shell thickness-dependent photoluminescence peaks and energy relaxations in semiconductor quantum dots (QDs). The surface effect plays an important role in the formation of new states - polaronic states around the surface of QDs. The polaronic states formed emit light due to the strong interaction between the core state (confined state) and the surface state with an enhanced participation of the size effect.