4,330 research outputs found
Superconductivity devices: Commercial use of space
The high T(sub c) superconducting ceramic materials, developed in 1987, are now being extensively investigated for a variety of engineering applications. These applications include such devices as conducting links, rotating and linear bearings, sensors, filters, switches, high Q cavities, magnets, and motors. Some of these devices take advantage of the material's ability to lose all electrical resistance at a critical temperature, T(sub c), while others make use of the repulsion forces generated between the magnetic field of a permanent magnet and a superconductor which is cooled below its T(sub c), Meissner effect. This report describes the work accomplished to date by: (1) reviewing the present state of the art in actuator technology, (2) evaluating processing and fabrication of high strain electrostrictive materials, and (3) testing these electrostrictive materials
Superconductivity devices: Commercial use of space
High T sub C superconducting thick film were prepared by a screen printing process. Y-based (YBa2Cu3O(7-x) superconducting thick film were printed on 211/Al2O3, SNT/Al2O3, and YSZ substrates. Because of poor adhesion of the superconductor thick films to 211/Al2O3 and SNT/Al2O3 substrates, relatively low T sub C and J sub C values were obtained from the films printed on these substrates. Critical temperatures (T sub C) of YBa2Cu3O(7-x) thick films deposited on 211/Al2O3 and SNT/Al2O3 substrates were about 80 K. The critical current densities (J sub C) of these films were less than 2 A/sq cm. Higher T sub C and J sub C YBa2Cu3O(7-x) thick films were printed on YSZ substrates. A YBa2Cu3O(7-x) thick film with T sub C=86.4 and J sub C= 50.4 A/sq cm was prepared by printing the film on YSZ substrate and firing at 990 C for 10 minutes. Multiple-lead samples were also prepared on the YSZ substrates. The multiple-lead samples showed lower T sub C and/or J sub C values than those of the plain samples. The electrical properties of YBa2Cu3O(7-x) thick films were determined by the microstructures of the films. The YBa2Cu3O(7-x) thick films printed on the YSZ substrates, which had the best properties among the films printed on the three different kinds of substrates, had the highest density and the best particle interconnection. The YBa2Cu3O(7-x) thick films with preferred orientation in (001) direction were obtained on the YSZ substrates. Cracks, which retard the properties of the films, were found from the films deposited on the YSZ substrates. Currently, a MSZ (Magnesium Stabilized Zirconia) substrate, which had higher thermal expansion coefficient than the YSZ substrate, is used as substrate for the YBa2Cu3O(7-x) thick film in order to eliminate the cracks on the film. Bi-based superconductor thick films were printed on polycrystalline MgO and YSZ substrates. Interactions between BSCCO thick films and the YSZ substrates were observed. Various buffer layer materials were applied onto the substrates in order to avoid the interactions between the BSCCO thick films and the ZrO2-based substrates. So far, a BSCCO printed on MgO substrate with T Sub C=89K was obtained. The J sub C of the film was lower than 0.1 A/sq cm by reason of poor interconnectivity of the BSCCO particles
Structural and electrical transport properties of superconducting Au{0.7}In{0.3} films: A random array of superconductor-normal metal-superconductor (SNS) Josephson junctions
The structural and superconducting properties of Au{0.7}In{0.3} films, grown
by interdiffusion of alternating Au and In layers, have been studied. The films
were found to consist of a uniform solid solution of Au{0.9}In{0.1}, with
excess In precipitated in the form of In-rich grains of various Au-In phases
(with distinct atomic compositions), including intermetallic compounds. As the
temperature was lowered, these individual grains became superconducting at a
particular transition temperature (Tc), determined primarily by the atomic
composition of the grain, before a fully superconducting state of zero
resistance was established. From the observed onset Tc, it was inferred that up
to three different superconducting phases could have formed in these
Au{0.7}In{0.3} films, all of which were embedded in a uniform Au{0.9}In{0.1}
matrix. Among these phases, the Tc of a particular one, 0.8 K, is higher than
any previously reported for the Au-In system. The electrical transport
properties were studied down to low temperatures. The transport results were
found to be well correlated with those of the structural studies. The present
work suggests that Au{0.7}In{0.3} can be modeled as a random array of
superconductor-normal metal-superconductor (SNS) Josephson junctions. The
effect of disorder and the nature of the superconducting transition in these
Au{0.7}In{0.3} films are discussed.Comment: 8 text pages, 10 figures in one separate PDF file, submitted to PR
Interface induced high temperature superconductivity in single unit-cell FeSe films on SrTiO3
Searching for superconducting materials with high transition temperature (TC)
is one of the most exciting and challenging fields in physics and materials
science. Although superconductivity has been discovered for more than 100
years, the copper oxides are so far the only materials with TC above 77 K, the
liquid nitrogen boiling point. Here we report an interface engineering method
for dramatically raising the TC of superconducting films. We find that one
unit-cell (UC) thick films of FeSe grown on SrTiO3 (STO) substrates by
molecular beam epitaxy (MBE) show signatures of superconducting transition
above 50 K by transport measurement. A superconducting gap as large as 20 meV
of the 1 UC films observed by scanning tunneling microcopy (STM) suggests that
the superconductivity could occur above 77 K. The occurrence of
superconductivity is further supported by the presence of superconducting
vortices under magnetic field. Our work not only demonstrates a powerful way
for finding new superconductors and for raising TC, but also provides a
well-defined platform for systematic study of the mechanism of unconventional
superconductivity by using different superconducting materials and substrates
Self-fields in thin superconducting tapes: implications to the thickness effect in coated conductors
Most applications of superconductors, such as power transmission lines,
motors, generators, and transformers, require long cables through which large
currents circulate. Impressive progress has recently been achieved in the
current-carrying capability in conductors based on high-temperature
superconductors. Coated conductors are likely the best examples, consisting of
very good quality thin layers of YBCO superconductor grown on top of a metallic
tape with some intermediate layers. However, there is an important problem for
achieving large currents: a large decrease in transport critical-current
density Jc when increasing film thickness has been observed in coated
conductors made by all available techniques. Here, we theoretically explain the
nature and the ubiquitous presence of this so-called thickness effect by
analyzing the self-field created by the transport currents in the
superconductor, assuming a realistic field-dependent Jc. This knowledge can
help finding new ways to improve transport current in thick superconducting
films.Comment: 7 pages, 3 figure
Superconducting properties of MgB2 thin films prepared on flexible plastic substrates
Superconducting MgB2 thin films were prepared on 50-micrometer-thick,
flexible polyamide Kapton-E foils by vacuum co-deposition of Mg and B
precursors with nominal thickness of about 100 nm and a special ex-situ rapid
annealing process in an Ar or vacuum atmosphere. In the optimal annealing
process, the Mg-B films were heated to approximately 600 C, but at the same
time, the backside of the structures was attached to a water-cooled radiator to
avoid overheating of the plastic substrate. The resulting MgB2 films were
amorphous with the onset of the superconducting transition at T_(c,on) about 33
K and the transition width of approximately 3 K. The critical current density
was > 7x10^5 A/cm^2 at 4.2 K, and its temperature dependence indicated a
granular film composition with a network of intergranular weak links. The films
could be deposited on large-area foils (up to 400 cm^2) and, after processing,
cut into any shapes (e.g., stripes) with scissors or bent multiple times,
without any observed degradation of their superconducting properties.Comment: 3 figure
Recent developments in the characterization of superconducting films by microwaves
We describe and analyze selected surface impedance data recently obtained by
different groups on cuprate, ruthenate and diboride superconducting films on
metallic and dielectric substrates for fundamental studies and microwave
applications. The discussion includes a first review of microwave data on MgB2,
the weak-link behaviour of RABiTS-type YBa2Cu3O7-d tapes, and the observation
of a strong anomalous power-dependence of the microwave losses in MgO at low
temperatures. We demonstrate how microwave measurements can be used to
investigate electronic, magnetic, and dielectric dissipation and relaxation in
the films and substrates. The impact of such studies reaches from the
extraction of microscopic information to the engineering of materials and
further on to applications in power systems and communication technology.Comment: Invited contribution to EUCAS2001, accepted for publication in
Physica C in its present for
Construction of a Versatile Ultra-Low Temperature Scanning Tunneling Microscope
We constructed a dilution-refrigerator (DR) based ultra-low temperature
scanning tunneling microscope (ULT-STM) which works at temperatures down to 30
mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these
extreme operation conditions, this STM has several unique features not
available in other DR based ULT-STMs. One can load STM tips as well as samples
with clean surfaces prepared in a UHV environment to an STM head keeping low
temperature and UHV conditions. After then, the system can be cooled back to
near the base temperature within 3 hours. Due to these capabilities, it has a
variety of applications not only for cleavable materials but also for almost
all conducting materials. The present ULT-STM has also an exceptionally high
stability in the presence of magnetic field and even during field sweep. We
describe details of its design, performance and applications for low
temperature physics.Comment: 6 pages, 9 figures. accepted for publication in Rev. Sci. Instru
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Importance of low-angle grain boundaries in YBa2Cu3O7-delta coated conductors
Over the past ten years the perception of grain boundaries in YBa2Cu3O7-δ
conductors has changed greatly. They are no longer a problem to be eliminated but an
inevitable and potentially favourable part of the material. This change has arisen as a
consequence of new manufacturing techniques which result in excellent grain alignment,
reducing the spread of grain boundary misorientation angles. At the same time there
is considerable recent evidence which indicates that the variation of properties of grain
boundaries with mismatch angle is more complex than a simple exponential decrease in critical
current. This is due to the fact that low-angle grain boundaries represent a qualitatively
different system to high angle boundaries. The time is therefore right for a targetted
review of research into low-angle YBa2Cu3O7-δ grain boundaries. This article does
not purport to be a comprehensive review of the physics of grain boundaries as found in
YBa2Cu3O7-δ in general; for a broader overview we would recommend that the reader
consult the comprehensive review of Hilgenkamp and Mannhart (Rev. Mod. Phys., 74, 485,
2002). The purpose of this article is to review the origin and properties of the low-angle grain
boundaries found in YBa2Cu3O7-δ coated conductors both individually and as a collective
system.EPSR
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