Person:
Díaz-Guerra Viejo, Carlos

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First Name
Carlos
Last Name
Díaz-Guerra Viejo
URI
https://hdl.handle.net/20.500.14352/75094
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Física Aplicada
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1996 - 19974
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Author: Sadovskaya, N. V. × End date: 1999 ×

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Now showing 1 - 4 of 4
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    Cathodoluminescence microscopy and secondary electron emission in mechanically polished and electron irradiated YBa_2Cu_3O_(7-x) ceramics
    (Physica Status Solidi A-Applied Research, 1996) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Tomashpolsky, Y. Y.; Sadovskaya, N. V.
    Cathodoluminescence (CL) and secondary electron emission (SEE) in the scanning electron microscope have been used to study the effects of mechanical polishing and electron irradiation on YBa2Cu3O7-x ceramics. CL spectra from the mechanically polished superconductors show an enhanced 2.4 eV luminescence band, which is related to oxygen content redistribution or depletion. Electron irradiation induces strong morphological and compositional changes which are proposed to be connected with melting-resolidification processes and surface phase segregation. SEE yield measurements allow to detect an oxygen depleted area with stoichiometric cationic composition surrounding the irradiated region. CL spectra recorded from this oxygen-deficient area also show an enhanced 2.3 to 2.4 eV emission band in comparison with the spectra recorded from the non-irradiated material. Strongly luminescent non-superconducting phases appear in the irradiated regions, showing intense 3.1 and 0.78 to 0.81 eV emission bands.
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    Electron beam induced structural changes in bi_2Sr_2CaCu_2O_(8+x) studied by cathodoluminescence microscopy and secondary electron emission
    (Applied Physics A-Materials Science&Processing, 1997) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Tomashpolsky, Y. Y.; Sadovskaya, N. V.
    Bi_2Sr_2CaCu_2O_(8+x) superconducting ceramics have been irradiated in the scanning electron microscope (SEM), and the irradiation-induced effects investigated by cathodoluminescence (CL), secondary electron emission (SEE) and X-ray microanalysis. Electron beam irradiation causes a slight Bi depletion and an inhomogeneous Ca distribution. A higher CL intensity emission is found in the irradiated areas, where besides an enhancement of the oxygen content related 2.4 eV band, another CL bands probably related to new non-superconducting phases induced by irradiation can be observed. SEE yield measurements allow to detect an oxygen depleted region surrounding the irradiated areas. X-ray microanalysis shows that this intermediate region retains the cationic composition of the unaffected material. CL spectra from bright zones inside the same area also show a dominant 2.4 eV emission band, which supports its relation with oxygen deficiency or rearrangement in high-T-c superconductors.
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    Electron beam induced compositional and structural changes in Tl_2Ba_2CuO_(6+σ)
    (Superconductor Science & Technology, 1996) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Tomashpolsky, Y. Y.; Sadovskaya, N. V.; Opagiste, C.
    Tl_2Ba-2CuO_(6+σ) ceramics have been irradiated in a scanning electron microscope. The resultant changes in the cationic stoichiometry and oxygen content of the samples were investigated by cathodoluminescence (CL), secondary electron emission (SEE) and EDX microanalysis. ii depletion and Ba enrichment are observed in the irradiated areas. CL spectroscopy shows that irradiation causes the increase of a 540 nm emission band attributed to complex centres involving oxygen vacancies. Other features of the CL spectra strongly suggest the presence of radiation induced new phases. The SEE yield, Delta, has been found to depend on the oxygen content of the samples This dependence can be explained on the basis of two charge carrier subsystems and their mutual interaction, Measurements of ∆ allow us to detect an oxygen deficient region, sometimes extending up to a distance of about 1000 mu m, that surrounds the irradiated material.
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    Structural and composition changes in superconducting ceramics locally irradiated by electrons
    (Physics of the Solid State, 1997) Tomashpolskii, Y. Y.; Sadovskaya, N. V.; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Opagiste, C.
    The structural changes and the cation and anion compositions of the surface of superconducting YBa_2Cu_3O_(7-x) and Tl_2Ba_2CuO_(6+x) ceramics after local irradiation for several seconds by an electron probe with an accelerating voltage of 25 kV and a current exceeding 10(-7) A are investigated by secondary-electron emission and by cathodoluminescence and x-ray microanalysis in a scanning electron microscope, Morphologically altered regions are detected in the irradiation epicenter, where the structure, chemical composition, and phase composition of the original compound are completely lost. In the intermediate zone between the epicenter and the periphery a distribution of the secondary emission yield is observed with a complex character that differs for the yttrium and thallium ceramics, and anomalies appear in the cathodoluminescence spectra, The experimental data are interpreted on the basis of ideas of oxygen losses under the direct influence of the electron probe and related electronic processes in superconductors.