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EnglishHigh-resolution x-ray powder diffraction and extended x-ray-absorption fine-structure EXAFS measurements have been performed on the iso-structural framework crystals Cu2O and Ag2O as a function of temperature. According to diffraction, both compounds exhibit a negative thermal expansion NTE of the lattice parameter over extended temperature intervals from 9 to 240 K for Cu2O, up to 470 K for Ag2O and anisotropic thermal displacements of M atoms M=Cu,Ag. EXAFS measures a positive expansion of the nearest-neighbors M-O pair distance and a perpendicular to parallel anisotropy of relative motion, much stronger than the anisotropy of the absolute M motion. The M-O bond is much stiffer against stretching than against bending. According to EXAFS, out of the 12 M-M next-nearest-neighbor pairs, the 6 connected via a bridging oxygen undergo negative expansion, while the 6 lacking the bridging oxygen undergo positive expansion. These results show a rather complex local behavior, which, while confirming the connection of NTE to strong perpendicular vibrations, is inconsistent with rigid unit modes models and suggests a more flexible model based on rigid M-O rods.
| Titolo: | Negative thermal expansion and local dynamics in Cu2O and Ag2O |
| Autori: | Sanson, Andrea; Rocca, Francesco; Dalba, Giuseppe; Fornasini, Paolo; Grisenti, Rolly; M., Dapiaggi; G., Artioli |
| Autori Unitn: | |
| Titolo del periodico: | PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS |
| Anno di pubblicazione: | 2006 |
| Codice identificativo Scopus: | 2-s2.0-33745283386 |
| Codice identificativo ISI: | WOS:000238696200064 |
| Digital Object Identifier (DOI): | 10.1103/PhysRevB.73.214305 |
| Handle: | http://hdl.handle.net/11572/91213 |
| Appare nelle tipologie: | 03.1 Articolo su rivista (Journal article) |
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