Search results for "ABSORPTION FINE-STRUCTURE"
showing 4 items of 4 documents
Negative thermal expansion in cuprite-type compounds: A combined synchrotron XRPD, EXAFS, and computational study of Cu2O and Ag2O
2006
Cuprite-type oxides (Cu2O and Ag2O) are framework structures composed by two interpenetrated networks of metal-sharing M4O tetrahedra (M = Cu, Ag). Both compounds exhibit a peculiar negative thermal expansion (NTE) behaviour over an extended temperature range (9 240 K for Cu2O, 30-470 K for Ag2O). High-accuracy synchrotron powder diffraction and EXAFS measurements were performed from 10 K up to the decomposition temperature to understand the nature of the NTE effects. The critical comparison of the diffraction and absorption results concerning the temperature dependence of the interatomic distances and of the atomic vibrational parameters proves to be fundamental in defining the local dynam…
Multiple scattering approach for two-electron resonant emission studied by angle-resolved coincidence spectroscopy.
2008
International audience; We have developed a generalization of the multiple-scattering formalism to deal with Auger-photoelectron coincidence spectroscopy APECS in the solid state. We have merged the exact atomic treatment of the angular correlations between the two electrons and the single-particle approach, on which the multiplescattering description of condensed matter relies. This allows the recovering, even in extended systems, of the entangled form of the electron-pair wave function characterizing the coincidence angular diffraction pattern. In the atomic limit our formalism correctly reproduces the cross section, as calculated within the statistical-tensors approach, usually employed …
Decorated pottery study: Analysis of pigments by x-ray absorbance spectroscopy measurements
2007
Characterization of pigments on decorated pottery fragments has been fully carried out by nondestructive x-ray absorbance spectroscopy (XAS). The samples were a series of pottery shards excavated from the archeological site of Caltagirone (Sicily, Italy), a well-known ceramic production center. Aesthetical criteria and morphological observations allowed us to attribute the samples to quite different historical periods, starting from the 18th century B.C. up to the 16th century A.D. An extensive time interval led us to suppose that different materials and techniques were used for the production of the ceramic paste and also for the preparation of pigments. XAS measurements were performed at …
X-ray absorption spectroscopy study of local dynamics and thermal expansion in ReO3
2015
The thermal expansion of polycrystalline ${\mathrm{ReO}}_{3}$ is studied in vacuum by x-ray diffraction from 300 to 600 K and by extended x-ray absorption fine structure (EXAFS) at the Re ${L}_{3}$ edge from 30 to 600 K. A detailed EXAFS analysis is presented up to the sixth coordination shell around Re. The crystal thermal expansion is weak throughout the explored range, negative below 100 K, positive from 150 to 500 K, and negative again above 500 K. The analysis of mean square relative displacements obtained by EXAFS and of mean square displacements available from x-ray and neutron diffraction measurements confirms the presence of significant static disorder in the investigated samples. …