Application of Optical Techniques in the Characterization of Thermal Stability and Environmental Degradation in High Temperature Superconductors

This Book Contains A Collection Of Works Intended To Study Theoretical And Experimental Aspects Of Superconductivity. Here You Will Find Interesting Reports On Low-tc Superconductors (materials With Tc 30 K), As Well As A Great Number Of Researches On High-tc Superconductors (materials With Tc 30 K). Certainly This Book Will Be Useful To Encourage Further Experimental And Theoretical Researches In Superconducting Materials. These results show that optical techniques are valuable tools to obtain information about the behaviour of superconducting materials, relevant to the design of different technological applications. In particular, problems with quench generation and environmental degradation have been studied. DSPI can be used to visualize different heat generation processes that take place in superconducting materials depending on the cooling conditions. It can be used to detect where a hot spot will take place before damaging the sample. In consequence, it can help to find out which are the microstructural defects that are more important in heat generation and propagation. This has been applied in the analysis of bulk Bi-2212 monoliths and 2G HTS wires. In the case of bulk materials this information can be used to modify the processing parameters in order to eliminate these defects or to distribute them in the sample in order to homogenise the transition to the normal state. In the case of 2G HTS wires DSPI measurements visualize if the sample presents a homogeneous or an inhomogeneous transition to the normal state. This information has been confirmed with the direct measurement of the electric field and temperatures profiles. The main advantage is that DSPI does not require soldering voltage taps or thermocouples in the sample. One of the objectives for the future research is to obtain quench parameters from the optical observations. This is not a simple task because the deformations that are observed also depend on the sample mechanical constraints. For this reason, in order to obtain quantitative information from these measurements, thermo-mechanical models are being developed in order to be able of determining the temperature profile from the mechanical deformation. DSP has provided useful information about environmental degradation of bulk superconducting materials. The chemical reactions that take place modify the surface characteristics and, in consequence, reduce the correlation coefficient values. The main advantage of this technique in comparison with other experimental techniques is that it provides 2D local information in the very early stages of the degradation process. In addition, if the reference image is changed from the initial state to any other at a given time Important improvements have been accomplished recently concerning a detailed description and evaluation of the gamma radiation damage effects in solids, and particularly in high Tc superconductors, were Monte Carlo simulation tools have been introduced in different approaches. In Monte Carlo assisted Classical Method approach, MCCM, the OenHolmes-Cahn classical atom displacement rate calculation algorithm was expanded. For this, secondary electron in-depth energy profiles calculated by means of Monte Carlo based codes was introduced, particularly to YBCO superconducting material. On the other side, a new theoretical description of the conditions favoring the occurrence of single fast electron elastic scattering in solids has been developed. Further works in this field are in course, comparing this new atom displacements rate calculation algorithm with previous ones, like MCCM. On the basis of MCCM approach, gamma quanta induced YBCO in-depth atom displacement rate distributions were calculated up to incident energies lower than 10 MeV. At very low incident energies, oxygen atom displacements take place on Cu(1)-O chain sites. With increasing incident energy, firstly Oxygen displacements in Cu(2)-O2 planes and other crystalline sites, while at higher energies Cupper displacements are also induced, which begins to be dominant at about 4 MeV and reaches a maximum contribution of 65% at 10 MeV. The corresponding in-depth dpa profiles at different incident energies due to electrons and positrons were characterized as being very similar. It was concluded, that gamma radiation induced oxygen displacements in both, Cu(2)-O2 planes and Cu(1)-O chains, as well as secondary electrons are eventually trapped in unoccupied O(4) in Cu(1)-O chain sites in basal planes, favoring oxygen rich nearest neighbor configuration around the Cu(1) sites, provoking a strengthening of the We believe that the simple model proposed in this paper in the case of p-type oxide superconductors could also be extended to estimate the optimal doping of n-type oxide superconductors. However, in the case of n-type oxide superconductors, the reaction produced by oxygen doping is a reduction reaction instead of an oxidation reaction that occurs in p-type oxide superconductors. Since we have not found in the literature any experimental determination of the oxygen content in the case of n-type oxide superconductors we shall not discuss this issue here. This question will be addressed in a future work. We have proposed a simple model to estimate the relative concentrations of the ions involved to estimate the oxygen content for optimal doping of p-type oxide superconductors. The predictions based on this model are in good agreement with experimental results reported in the literature (Table 3). However, we emphasize that this simple model is not a theoretical model, it is a phenomenological model. In Sections 5, 6, 7 and 8 we have discussed some questions in order to give theoretical support for this model Impressum_Superconductor.indd......Page 1 01_Luiz......Page 11 02_Shepelev......Page 27 03_Paul......Page 57 04_Bagraev......Page 79 05_Zhang......Page 103 06_Li......Page 121 07_Hernandez......Page 145 08_Bandyopadhyay......Page 171 09_Angurel......Page 189 10_Miryala......Page 213 11_Aldica......Page 239 12_Muhammad......Page 259 13_Takahashi......Page 273 14_Cataltepe......Page 283 15_Ozdemir......Page 301 16_Kuo......Page 321 17_Gainov......Page 337