Person: Díaz-Guerra Viejo, Carlos
Loading...
First Name
Carlos
Last Name
Díaz-Guerra Viejo
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Física Aplicada
Identifiers
4 results
Search Results
Now showing 1 - 4 of 4
Item 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.Item Cathodoluminescence microscopy of superconducting and non-superconducting Tl_2Ba_2CuO_(6+ δ) polycrystals(Physica C, 1996) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Opagiste, C.Luminescence properties of Tl_2Ba_2CuO_(6+ δ) samples with different superconducting transition temperatures have been studied by cathodoluminescence (CL) in the scanning electron microscope. Independent of the crystal structure, tetragonal or orthorhombic, the Cl spectra show two resolved bands at about 430 nm (2.9 eV) and 540 nm (2.3 eV), respectively. The results show that the 2.3 eV emission is related to oxygen content and is more intense in low-oxygen content superconducting samples. It is proposed that this band is related to a complex center involving oxygen vacancies. A comparison of spectra from Tl_2Ba_2CuO_(6+ δ) and from precursors used in the synthesis (CuO_x, Tl_2Ba_2O_5) has been carried out.Item 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.Item Cathodoluminescence and photoluminescence studies of sintered BaCuO_2(Journal of Luminescence, 1997) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; García, J. A.; Remon, A.; Opagiste, C.The capability of luminescence techniques to characterize BaCuO_2 and in particular to detect the presence of this compound as impurity phase in high-T-c superconductors (HTSC) has been investigated. Cathodoluminescence (CL) in the scanning electron microscope and photoluminescence (PL) have shown that the luminescence emission of BaCuO_2 can be separated from those of Y-, Bi- and Tl-based HTSC. The main luminescence bands and their decay times in BaCuO_2 are described.