[en] The authors describe here the first observation of terahertz emission from unbiased YBa₂Cu₃O_7-δ (YBCO) thin films. These films are excited by 150 fs, 1.5 eV and 3.0 eV, optical pulses for a range of temperatures, T, 4 K < T < 300 K and for a range of oxygen doping from optimally-doped (δ = 0) to insulating (δ = 0.8). They demonstrate that this emission is generated by optical rectification due to the bulk electric quadrupole source term, comprising the first observation of such a source term in terahertz emission

[en] Bismuth-based superconductors ar now thoroughly studied and are thought to be one of the best High Critical Temperature Superconductors (HSTC) that could be industrially developed. Though their synthesis is one of the easiest to achieve, their strong anisotropy affects drastically their transport properties under magnetic field, especially in the low field regime. In order to avoid vortices motion, two main methods have been used to introduce pinning centers: irradiation defects or dissemination of non-superconducting particles. An original method of synthesis has been developed in our laboratories, alternating electrolytic depositions and heat treatments with which one can obtain Bi 2212 tapes on silver substrate. Though we have good performances at 77 K, the J_c drops by a factor of 5 at 7 T for B parallel to c-axis. By including Ag, MgO and ZrO₂ particles, we tried to introduce efficient pinning centers in the superconducting matrix. Some of these dopants played also a role on intergranular connectivity. By magnetisation and transport studies, we have been able to improve the situation in these two fields. (author)

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[en] Thermally stimulated current (TSC) techniques provide information about oxide-trap charge densities and energy distributions in MOS capacitors exposed to ionizing radiation or high-field stress that is difficult or impossible to obtain via standard capacitance-voltage or current-voltage techniques. The precision and reproducibility of measurements through repeated irradiation/TSC cycles on a single capacitor is demonstrated with a radiation-hardened oxide, and small sample-to-sample variations are observed. A small increase in E5' center density may occur in some non-radiation-hardened oxides during repeated irradiation/TSC measurement cycles. The importance of choosing an appropriate bias to obtain accurate measurements of trapped charge densities and energy distributions is emphasized. A 10 nm deposited oxide with no subsequent annealing above 400 ampersand deg;C shows a different trapped-hole energy distribution than thermally grown oxides, but a similar distribution to thermal oxides is found for deposited oxides annealed at higher temperatures. Charge neutralization during switched-bias irradiation is found to occur both because of hole-electron annihilation and increased electron trapping in the near-interfacial Si0₂. Limitations in applying TSC to oxides thinner than 5 nm are discussed

[en] High critical current YBa₂Cu₃O_7-y (referred to as YBCO) coated conductors were fabricated with a layer sequence of YBCO/YSZ/CeO₂/Ni. The cube (100) texture in the starting Ni substrates was obtained by cold rolling followed by recrystallization. A thin CeO₂ (Cerium Oxide) layer with a thickness of 100-200 was grown epitaxially on the biaxially textured-Ni substrates using an e-beam evaporation technique. This was followed by the growth of a thick (<= 0.77 m) YSZ (Yttria Stabilized Zirconia) layer using either e-beam evaporation or rf magnetron sputtering. The e-beam CeO₂ film had a dense microstructure. The microstructure of the e-beam YSZ film was porous whereas the sputtered YSZ film was dense. The YBCO films were grown by pulsed laser deposition on both e-beam and sputtered YSZ layers. A transport critical current density of 1 x l0⁶ A/cm² at 77 K was obtained for 0.8 m thick YBCO Rims on both YSZ surfaces in zero field. To demonstrate the quality and compatibility of the e-beam CeO₂ layers; YBCO films were also grown on CeO₂-buffered YSZ (100) single crystal substrates using e-beam co-evaporated Y-BaF₂-Cu precursors followed by a post-annealing process. A transport critical current density of over 1 x lO⁶A/cm² at 77 K was obtained on a 0.3 m thick YBCO film in zero field

[en] It is demonstrated that a combination of neutron irradiation with uranium doping introduce fission tracks through a Bi-2223 tape which act as effective pinning centres, leading to a substantial increase in critical current. Preliminary data suggests that the combination of uranium doping and neutron irradiation produces improved flux pinning in Bi-2223 tapes over neutron irradiation alone. Before irradiation, SEM, DTA and XRD analyses were performed on the tapes. Both before and after irradiation the trapped maximum magnetic flux was measured at 77K. Before neutron irradiation, uranium doping has no effect on critical current. Preliminary SEM data suggested that the uranium is homogeneously distributed throughout the oxide core of the tape. The presence of 2212 and other secondary phases in the doped tapes suggest further refinement of the sintering procedure is necessary. (authors)

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[en] Thermal conductivity of zirconia based inert matrix and analogous fuel materials were measured and modelled. Measurements were performed using the laser flash method and systematically applied for binary and ternary zirconia-yttria-erbia as well as quaternary systems including thoria or ceria. Measurements were carried out from room temperature to 1250 K. Thermal conductivity was also modelled taking into account the dopant effect on the lattice parameter of the cubic solid solution, the oxygen vacancy size and their concentration. Experimental and modelled lattice parameter values are compared prior to full justification of the results. In the temperature range from 300 to 950 K, the thermal conductivity of the single phase solid solution with yttria, erbia and ceria as analogous fuel material is about 2 W·m^-1K^-1. Energy transfer in these materials is discussed on the basis of both photonic and phononic conductivities. (author)