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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

High temperature superconductors in electromagnetic applications

Richens, P. E. January 2000 (has links)
No description available.
22

High-temperature thermoelectric properties of Ca0.9−xSrxYb0.1MnO3−delta (0<=x<=0.2)

Kosuga, Atsuko, Isse, Yuri, Wang, Yifeng, Koumoto, Kunihito, Funahashi, Ryoji 13 May 2009 (has links)
No description available.
23

A study of the effects of oxygen environment on the stoichiometry, phase assemblage and stability of BiSCCO 2212 and 2201 using EPMA

Rowan, Fraser S. January 2001 (has links)
A method of performing accurate oxygen analysis on cuprate based superconducting materials was established using electron probe micro analysis (EPMA). A range of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>δ</sub> ceramics with varying oxygen concentration were used to test the method. Using YBCO as a reference material, a suitable standard for oxygen analysis of Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>δ</sub> (BiSCCO-2212) materials was obtained. This standard was used to perform full elemental analysis of a range of BiSCCO-2212 crystals, post annealed in pO<sub>2</sub>'s between 10<sup>-5</sup>-2atm. When the average Cu valence of each crystal was calculated and plotted as a function of the critical temperature (T<sub>c</sub>) for each crystal, it was shown that BiSCCO-2212 materials conformed to the 'universal' trend illustrated by most other HTS and did not exhibit anomalous behaviour as had been previously believed. The phase assemblage and superconducting properties of BiSCCO-2212 Ag-clad multifilamental wires, prepared using the powder-in-tube (PIT) method by BICC, were studied as a function of a time/temperature profile. pO<sub>2</sub> of the processing atmosphere was found to be the predominant factor in determining the stoichiometry of the 2212 phase within wires. The phase assemblage is not simply a function of pO<sub>2</sub> as previously believed and can be controlled, in part, by the post annealing temperature. Homogenisation of the phase assemblage in BiSCCO-2212 Ag-clad wires can be achieved by prolonged heating (96hrs) at an appropriate temperature. An investigation into the 10K superconducting BiSCCO phase has shown the Sr-rich solid solution to extend towards the ideal stoichiometry of 2:2:1 (Bi:Sr:Cu) with increasing pO<sub>2</sub>. Using a combination of high pO<sub>2</sub> (60atm) to achieve the appropriate Bi:Sr stoichiometry followed by post annealing in N<sub>2</sub> to adjust the oxygen content, it was possible to prepare single-phase ceramics of stoichiometry Bi<sub>2.11(2)</sub>Sr<sub>1.90(2)</sub>Cu<sub>0.99(2)</sub>O<sub>δ</sub> with a T<sub>c</sub>=10.5K(5).
24

Ultrafast processes in high temperature superconductors

Gay, Pierre January 2000 (has links)
Using time-resolved photo-induced reflectivity, we reported for the first time a systematic work on the ultrafast response of Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+δ</sub> (BSCCO-2212) and Tl<sub>2</sub>Ba<sub>2</sub>CuO<sub>6+δ</sub> (TBCO-2201), measurements of detwinned YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> (YBCO-123) single crystal with the electric field ̲E parallel to the a and b-axis and high-resolution measurements of the rising edge dynamics of YBCO-123 thin films. We identified similar photo-induced responses for BSCCO, TBCO and for YBCO with ̲E ⊥ ̲b, which indicates that we observed a universal response of HTSC coming from the CuO2 superconducting planes. This latter dynamics is composed of three different components corresponding to the superconducting, pseudogap and normal state. A bi-molecular model has been put forward to explain the linear temperature dependence of the decay rate; the model implies that the re-formation of the condensate is limited by the rate at which quasiparticle interact. Moreover, we observed superconducting fluctuations up to 13K above T<sub>c</sub> and a divergence of the long-lived component magnitude at very low temperature, which is explained by a cw heating model. In the pseudogap state, we have several indications that the negative peak observed between T<sub>c</sub> and T* has a different origin from that of the superconducting signal below T<sub>c</sub>. We argued that the probe mechanism of the pseudogap signal is electronic excitations of the pseudogap correlations. In the normal state, the observed dynamics is similar to that of simple metals. In the second part of this thesis, the rising edge dynamics of YBCO has been resolved in time. The model developed to interpret the results implies that the hot quasiparticles relaxation time down to the Fermi energy is 55fs. In this context, we proved that the Mazin model cannot explain both the oscillatory and the non-oscillatory part of the dynamics in YBCO. Finally, in YBCO-123, a new response has been observed with ̲E ∥ ̲b. We argued that the origin of this component is intraband transitions. This dynamics is solely responsive to the pseudogap, coming from the difference in scattering rate between pre-formed pairs and quasiparticles in the Drude reflectivity. The response with ̲E ⊥ ̲b exhibits a strong a-b plane anisotropy in its long-lived component, which can be interpreted as a d-wave gap symmetry using the thermally-activated model.
25

An investigation of stoichiometetry and thermo-mechanical processing parameters of (Pb,Bi)←2Sr←2Ca←2Cu←3O←x superconducting tapes

Feltham, Stuart Paul January 2001 (has links)
No description available.
26

Magnetic separation using high-T←c superconductors

Bolt, Livia January 2001 (has links)
No description available.
27

The magnetic properties of superconductors

Lloyd, Sion January 1999 (has links)
No description available.
28

Characterisation of practical high temperature superconductors in pulsed magnetic fields and development of associated technology

Saleh, Paul Matthew January 2000 (has links)
No description available.
29

Doped alkaline earth (nitride) hydrides

Verbraeken, Maarten Christiaan January 2009 (has links)
The work in this thesis relates to the preparation and structural and electrical characterisation of calcium and strontium hydrides, imides and nitride hydrides. Conventional solid state methods in controlled atmospheres were used to synthesise these materials. High temperature neutron diffraction, thermal analysis and conductivity studies performed on calcium and strontium hydride suggest an order – disorder transition in these materials at 350 – 450°C. Disordering is believed to involve rapid exchange of hydride ions across two crystallographic sites. This manifests itself in a lowering of the activation energy for bulk hydride ion conduction. The hydride ion conduction is good in these undoped materials: σ[total]subscript = 0.01 S/cm for CaH₂ at 1000K; for SrH₂, σ[total]subscript = 0.01 S/cm at 830K. Doping of SrH₂ with NaH causes a significant increase in the low temperature conductivity, due to presence of extrinsic defects. The high temperature conductivity is negatively affected by NaH doping. Calcium nitride hydride (Ca₂NH) was obtained as a single phase material by reacting either calcium metal or calcium hydride (CaH₂) in an argon atmosphere containing 5 – 7% H₂ and 1 – 7% N₂. Imide ions substituting for hydride and nitride ions constitute a major chemical defect in this material. Long range ordering of the nitride and hydride ions occurs, giving rise to a double cubic crystal symmetry. This order breaks down at 600 – 650°C. Applying the same reaction conditions to strontium metal results in a mixed phase of strontium nitride hydride and imide. No long range order in the nitride hydride phase could be observed. Doping Ca₂NH with lithium hydride (LiH) causes the appearance of a second calcium imide phase, whereas doping with sodium hydride (NaH) increases the amount of imide ions as a defect in the nitride hydride structure, thereby decreasing the long range ordering of nitride and hydride ions.
30

Thermoelectric properties of electron doped SrO(SrTiO3)n (n=1,2) ceramics

Wang, Yifeng, Lee, Kyu Hyoung, Ohta, Hiromichi, Koumoto, Kunihito 18 May 2009 (has links)
No description available.

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