J.W. Li

The high-pressure synthesis and superconductivity of Pr0.5Ca0.5Ba2Cu3Oz

The bulk superconductorss of Ca-doped Pr-123 phase, Pr0.5Ca0.5Ba2Cu3Oz were prepared at 1000 degrees C under high pressure of 5GPa. The superconducting properties of the sample depend on the synthesis conditions. The sample synthesized under high oxygen pressure was a nearly single orthorhombic 123 phase, and shows a superconducting transition at 52K with a Meissner signal of 12%. However, the sample prepared under a reduced environment is a high purity tetragonal 123 phase and has a much higher critical temperature (T-c = 97K) than that in orthorhombic phase. The results demonstrate that suppression of superconductivity by Pr in bulk Pr-123 phase can be compensated by appropriate hole doping with Ca.

Epitaxial growth of Bi2Sr2-xLaxCuO6+δ thin films by RF-magnetron sputtering

Superconducting Bi2Sr2-xLaxCuO6+delta thin films were successfully deposited on (100) LaAlO3 and (100) SrTiO3 substrates by in situ RF-magnetron sputtering. The highest zero resistance temperature T-c0, reached 29 K. The film morphology is shown to be related with the sputtering gas pressure. The microstructures. of the films show ab-twinning. Atomic force microscopy image showed the films grow as terrace islands with no screw dislocation. For obtaining high quality La-2201 superconducting thin films, the sputtering gas pressure should be higher, and the compositions of the targets have to be modified by trial and error

Radial n-i-p structure SiNW-based microcrystalline silicon thin-film solar cells on flexible stainless steel

Radial n-i-p structure silicon nanowire (SiNW)-based microcrystalline silicon thin-film solar cells on stainless steel foil was fabricated by plasma-enhanced chemical vapor deposition. The SiNW solar cell displays very low optical reflectance (approximately 15% on average) over a broad range of wavelengths (400 to 1,100 nm). The initial SiNW-based microcrystalline (μc-Si:H) thin-film solar cell has an open-circuit voltage of 0.37 V, short-circuit current density of 13.36 mA/cm2, fill factor of 0.3, and conversion efficiency of 1.48%. After acid treatment, the performance of the modified SiNW-based μc-Si:H thin-film solar cell has been improved remarkably with an open-circuit voltage of 0.48 V, short-circuit current density of 13.42 mA/cm2, fill factor of 0.35, and conversion efficiency of 2.25%. The external quantum efficiency measurements show that the external quantum efficiency response of SiNW solar cells is improved greatly in the wavelength range of 630 to 900 nm compared to the corresponding planar film solar cells.

Superconductivity and ferroelectricity of Pb(Zr,Ti) O3/YBa2Cu3O7 integrated films

Abstract The superconductivity, ferroelectricity and dielectric properties of Pb(Zr,Ti)O 3 .YBa 2 Cu 3 O 7 integrated films fabricated by the DC/RF magnetron sputtering method have been investigated. The integrated films are homogeneous and epitaxially grown on the substrate. In a relatively broad band, from 120 to 1o kHz, the dielectric loss at 77 K was low. The PZT film exhibited saturation and remanence polarizations of 40 and 25 μC/cm 2 , respectively and a coercive field of 98 kV/cm. The zero resistance temperature T c0 did not decrease after an overlayer PZT was deposited onto the YBCO layer. But the T c0 was degraded when an ultrathin YBCO layer was used in the heterostructure and further degraded by ion milling.

La1.6Sr0.4CaCu2O4+delta Cl2-y superconductor synthesized at ambient pressure

A copper oxy-chloride superconductor La1.6Sr0.4CaCu2O4+deltaCl2-y is prepared at ambient pressure using the traditional solid state reaction method.

Structural, transport and magnetic properties of PrBa2−xSrxCu3O7-δ

Abstract Structural, electrical transport and magnetic properties of polycrystalline samples of PrBa 2−x Sr x Cu 3 O 7-δ were investigated. The results were discussed based on the variation of hybridization between Pr ions and O2p of the CuO 2 planes induced by Sr doping.

Magnetization investigation of phase separation in La2CuO4+δ system

Abstract Magnetization measurements were performed on Cu-, Sr-doped and undoped La 2 CuO 4+δ samples before and after electrochemical oxidation. Experimental results showed that different samples exhibited different behaviors at various phase separation stages. Possible explanation is presented.

Scaling behavior of magnetic hysteresis loops and critical current density in melt-textured (Y1−xPrx)Ba2Cu3O7−δ

Abstract Magnetization measurements are performed on MTG (Y 1−x Pr x )Ba 2 Cu 3 O 7−δ samples with x=0 and 0.08. The magnetic hysteresis loops and related critical current densities for different temperatures are found to exhibit scaling bejavior when H, M and J c are normalized correspondingly. It is shown that this behavior can be described qualitatively well for low scaled field ( h ) region based on an extended critical-state model. Also, Pr doping is found not to affect the scaling behavior itself in the investigated level.

Epitaxial growth of Bi2Sr2−xLaxCuO6+δ thin films by in-situ DC- and RF- magnetron sputtering

Abstract Bi2Sr2−xLaxCu1O6+δ (La-2201) thin films were prepared by magnetron sputtering process. The microstructures of the films are related to the sputtering gas pressure. For getting high quality 2201 superconducting thin films, sputtering gas pressure could not be very low, and the target composition needs compensated. A-b twinning structure was observed for film growing on well-aligned STO and LAO substrates, while the structure could absent on vicinal STO substrates.

The morphology and interfacial effects on the R-T curve of two unit-cell thick ultrathin YBa2Cu3O7−δ film

Abstract Two unit-cell thick ultrathin YBa2Cu3O7−δ films were grown on (100) SrTiO3 substrates with a 400 A thick PrBa2Cu3O7−δ buffer layer by DC magnetron sputtering. The morphology was observed by both scanning electron microscopy and atomic force microscopy. An island-like growth mode was found; the heights of the islands differ mostly from each other by the YBCO c-axis length or half of the c-axis length. The zero-resistance temperature Tc0 of the film is 35 K, with a transition width of about 40 K. The R-T curve in the superconducting transition state can be analyzed by the Kosterlitz-Thouless transition and fluctuation-enhanced conductivity, and in the normal state can be described by the effects of interface (surface) and buffer layer conductance.