Absolute values of the London penetration depth in YBa2Cu3O6+y measured by zero field ESR spectroscopy on Gd doped single crystals

Zero-field electron spin resonance (ESR) of dilute Gd ions substituted for Y in the cuprate superconductor YBa$_2$Cu$_3$O$_{\rm 6+y}$ is used as a novel technique for measuring the absolute value of the low temperature magnetic penetration depth $\lambda(T\to 0)$. The Gd ESR spectrum of samples with $\approx 1$ substitution was obtained with a broadband microwave technique that measures power absorption bolometrically from 0.5 GHz to 21 GHz. This ESR spectrum is determined by the crystal field that lifts the level degeneracy of the spin 7/2 Gd$^{3+}$ ion and details of this spectrum provide information concerning oxygen ordering in the samples. The magnetic penetration depth is obtained by relating the number of Gd ions exposed to the microwave magnetic field to the frequency-integrated intensity of the observed ESR transitions. This technique has allowed us to determine precise values of $\lambda$ for screening currents flowing in the three crystallographic orientations ($\hat a$, $\hat b$ and $\hat c$) in samples of Gd$_{\rm x}$Y$_{\rm 1-x}$Ba$_2$Cu$_3$O$_{6+{\rm y}}$ of three different oxygen contents ${\rm y}=0.993$ ($T_c = 89$ K), ${\rm y}=0.77$ ($T_c=75$ K) and ${\rm y}=0.52$ ($T_c=56$ K). The in-plane values are found to depart substantially from the widely reported relation $T_c\propto 1/\lambda^2$.Comment: 14 pages, 12 figures; version to appear in PR

EXTENSION DES POSSIBILITÉS QUANTITATIVES DE LAMICROANALYSE PAR UNE FORMULATION NOUVELLE DES EFFETS DE MATRICE

Quelques applications d'un nouveau modèle de calcul en microanalyse, combinant les effets d'absorption et de numéro atomique, sont présentées. Un accent particulier est mis sur l'amélioration notable des corrections d'absorption, ainsi que sur la possibilité d'aborder quantitativement l'étude d'échantillons chimiquement inhomogènes en profondeur.Some applications of a new model for microanalysis,involving a combined computation of absorption and atomic number effects, are presented. A special attention is paid to the improvement of absorption corrective factors. The capability of a genuine quantitative approach for studying in-depth chemical heterogeneities is also emphasized

ANALYSE D'ÉCHANTILLONS STRATIFIÉS À LA MICROSONDE ÉLECTRONIQUE

Quelques applications d'un nouveau modèle de calcul adapté à l'étude quantitative d'échantillons inhomogènes en profondeur sont présentées.Some applications of a new model allowing quantitative study of in-depth heterogeneous samples are presented

X-ray microanalysis of stratified specimens

To be published in Analytica Chimica ActaSIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1993 n.50 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Standardless x-ray analysis of bulk specimens

Communication to : 3rd workshop on modern developments and applications in microbeam analysis (EMAS 93), Rimini (Italy), May 9-13, 1993. To be published in Microchimica ActaSIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1994 n.66 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Analysis of high-temperature creep deformation in a polycrystalline nickel-base superalloy

International audienceA new quantitative method has been developed for the analysis of the high-temperature creep deformation of polycrystalline nickel-base superalloys. Local deformation was measured by means of microextensometry using ceramic square grids deposited on flat specimens thanks to an electron lithography technique. The efficiency of this method has been proved for tensile creep tests performed under vacuum at 750 degrees C and 525 MPa on the NR6 superalloy and for a wide range of creep strains. This study revealed localization of deformation at grain boundaries and slip bands within the grains. A specific analysis method based on image correlation was developed to quantify the local strain fields. Electron back-scatter diffraction analysis showed that grain boundary sliding is mainly concentrated at general grain boundaries

Quantitative EDS analysis in the SEM applying the XPP procedure

Tire de XIIth International congress for electron microscopy, Seattle (Calif.), August 12-18, 1990SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1990 n.99 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc