L.F. Li

Development and Test of 10.5 kV/1.5 kA HTS Fault Current Limiter

Superconducting Fault Current Limiter (SFCL) is an attractive appliance for modern electrical power system. A 10.5kV/1.5 kA three-phase HTS fault current limiter was developed by IEE, CAS. This improved rectifier-type SFCL with HTS coil of 6.25 mH is going on a demonstrated long-term reliable operation in a real 10.5 kV substation located in Hunan, China. In a three-phase-to-ground short circuit test of grid, the prospective fault current of 3.5 kA was limited to 635 A at the pre-setup short-circuit point successfully

Robust Manipulation of Magnetism in Dilute Magnetic Semiconductor (Ga,Mn)As by Organic Molecules.

We firstly demonstrated the organic molecular manipulation of the magnetism of (Ga, Mn)As. Mn-doped GaAs thin films with various thicknesses were grown by low-temperature molecular-beam epitaxy (LT-MBE), and organic charge-transfer molecules were deposited on the surface of (Ga, Mn)As films by either solution-based self-assembly or vacuum thermal evaporation, which led to large carrier density modulation, and significant changes in the Curie temperature (Tc) and magnetization (Ms). Electron donor (acceptor) molecules were found to decrease (increase) both Tc and Ms. Moreover, through proper preparation of the (Ga, Mn)As surface, self-assembled monolayer (SAM) patterns of organic molecules with sub-75 nanometer line width were successfully created via dip-pen nanolithography (DPN). These results could open a new pathway to control nano-scale manipulation of magnetism in DMS, with potential applications in reconfigurable, non-volatile and hybrid molecular nano-spintronics.

Near Full-Composition-Range High-Quality GaAs1–xSbx Nanowires Grown by Molecular-Beam Epitaxy

Here we report on the Ga self-catalyzed growth of near full-composition-range energy-gap-tunable GaAs1-xSbx nanowires by molecular-beam epitaxy. GaAs1-xSbx nanowires with different Sb content are systematically grown by tuning the Sb and As fluxes, and the As background. We find that GaAs1-xSbx nanowires with low Sb content can be grown directly on Si(111) substrates (0 ≤ x ≤ 0.60) and GaAs nanowire stems (0 ≤ x ≤ 0.50) by tuning the Sb and As fluxes. To obtain GaAs1-xSbx nanowires with x ranging from 0.60 to 0.93, we grow the GaAs1-xSbx nanowires on GaAs nanowire stems by tuning the As background. Photoluminescence measurements confirm that the emission wavelength of the GaAs1-xSbx nanowires is tunable from 844 nm (GaAs) to 1760 nm (GaAs0.07Sb0.93). High-resolution transmission electron microscopy images show that the grown GaAs1-xSbx nanowires have pure zinc-blende crystal structure. Room-temperature Raman spectra reveal a redshift of the optical phonons in the GaAs1-xSbx nanowires with x increasing from 0 to 0.93. Field-effect transistors based on individual GaAs1-xSbx nanowires are fabricated, and rectifying behavior is observed in devices with low Sb content, which disappears in devices with high Sb content. The successful growth of high-quality GaAs1-xSbx nanowires with near full-range bandgap tuning may speed up the development of high-performance nanowire devices based on such ternaries.

Martensitic transformation in ZrO2-based ceramics at cryogenic temperatures

The microstructural changes associated with the tetragonal to monoclinic martensitic transformation at cryogenic temperatures in sintered CeO2-ZrO2 ceramics containing 15.5-16.5 mol% CeO2 have been studied by means of TEM observations. X-ray diffraction analysis indicates that the stress-induced martensitic phase increases with decreases in both temperature and CeO2 content. The effects of martensitic morphologies, anti-phase boundaries (APBs) and various dislocation features on mechanical properties are also discussed in the paper.

Critical current density in GdBaCuO superconducting thin films prepared by d.c. magnetron sputtering using a single planar target

Abstract The critical current density in GdBaCuO superconducting thin films was studied at various temperatures and magnetic fields. The thin films of GdBaCuO, which were of high quality and reproducibility, were prepared in situ on (100) SrTiO 3 substrates by d.c. magnetron sputtering from targets of sintered materials. The best zero resistance transition temperature, T co , was 91.5 K and the critical current density at 77 K was 3 × 10 6 A cm −2 . The magnetic field dependence of the critical current was notably weaker for T co > 90 K samples than for T co

PROPERTIES OF SOME TOUGHENED, RADIATION STABLE EPOXY RESINS

Impregnating resins for use in fusion magnet technology are required to be radiation stable, have a long useable life together with some degree of toughness to minimise the risk of cracking during cool‐down. Some multi‐functional resins in combination with solid aromatic amines have, in the past, been shown to have lost little of their strength after a total absorbed dose of 200 MGy. Using resins that are known to be radiation stable with a liquid aromatic amine hardener, the effect of adding an aromatic epoxy resin as a reactive ‘toughening agent,’ to improve the toughness of otherwise brittle resins has been assessed. Boron free glass composites, using various amounts of added toughening agent were prepared by vacuum impregnation and a number of critical composite properties have been measured, at room temperature and at 77 K.

Transformation and fracture of ZrO2-based ceramics at low-temperatures

Abstract Fracture experiments were done on 3 mol% Y-TZP ceramics from room temperature to 4.2 K. X-ray diffraction analysis was used to study the phase contents of the ceramics. The monoclinic phase content and fracture toughness, K Ic , all increase with decreasing temperature, which is mainly due to the stress-induced transformation. On the other hand, the spontaneous transformation also takes a part in toughening.

Field Test and Demonstrated Operation of 10.5 kV/1.5 kA HTS Fault Current Limiter

Superconducting fault current limiter (SFCL) is an attractive appliance for modern electrical power system. Institute of Electrical Engineering (IEE) at the Chinese Academy of Science (CAS) has successfully demonstrated a three-phase HTS bridge-type fault current limiter (FLC) at a substation in Hunan, China. The FCL suppressed the fault current below 635 A successfully in a 3-phase-to-ground short-circuit field test. Since August 2005, it has been going on a demonstrated long-term reliable operation for one year in the live 110 kV/10.5 kV substation.

Structure and superconductivity of YBa2Cu3−xSnxO7

Abstract Magnetization measurements of the YBa2Cu3−xSnxO7 superconductor were performed at 4.2 K in magnetic fields up to 29 T. The critical current densities are deduced from irreversible magnetization and the pinning forces are evaluated. X-ray diffraction and EPMA analysis indicated that the sintered YBa2Cu3−xSnxO7 (0 ⩽ x ⩽ 0.2) consists of superconducting YBa2(Cu,Sn)xO7 (123) phase and a small amount of Y2BaCuO? (211) and CuO phases. Tin dissolves largely in the 123 phase. no new phase was formed. Sn-doped YBa2Cu5O7 appears to have a higher critical current density than the undoped compound at 4.2 K. This is considered to be due to the substitution of Sn for Cu in the 123 lattice, and the finely dispersed 211 particles in the 123 phase result in an increase of the pinning force.

Foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires on Si (111) by molecular-beam epitaxy

Epitaxial high-quality InAs/InSb axial heterostructure nanowires are of great interest due to their distinct advantages in fundamental research as well as applications in semiconductor electronic and quantum devices. Currently, nearly all the growth of InAs/InSb axial heterostructure nanowires is assisted with foreign catalysts such as Au, and work on foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires is lacking. Here we report on the growth of InAs/InSb axial heterostructure nanowires on Si (111) substrates by molecular-beam epitaxy without using any foreign catalysts. The Sb/In beam equivalent pressure (BEP) ratio is found to have important influence on the heterostructure nanowire morphology, and InSb nanowires can be epitaxially grown on InAs nanowire stems with a hexagonal prism and nanosheet-like shapes when the Sb/In BEP ratio varies from 10 to 20. Transmission electron microscopy studies reveal that the InAs nanowire stems have a mixture of zincblende (ZB) and wurtzite (WZ) crystal structures, while InSb nanowire parts have a pure ZB crystal structure free of stacking faults. Composition analysis of axial heterostructure nanowires provides clear evidence that the InSb nanowires are epitaxially grown on InAs nanowires in an In self-assisted vapor-liquid-solid manner. This study paves a new route for growing narrow-gap semiconductor heterostructures with strong spin-orbit interaction for the study of topological states, and the growth manner presented here is expected to be used to grow other In-based axial heterostructure nanowires.