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Persistent URL http://purl.org/net/epubs/work/36487
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Record Id 36487
Title Negative thermal expansion and local dynamics in Cu2O and Ag2O
Abstract High-resolution x-ray powder diffraction and extended x-ray-absorption fine-structure (EXAFS) measurements have been performed on the iso-structural framework crystals Cu<sub>2</sub>O and Ag<sub>2</sub>O 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 Cu<sub>2</sub>O, up to 470 K for Ag<sub>2</sub>O) 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.
Keywords Physics
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Language English (EN)
Type Details URI(s) Local file(s) Year
Journal Article Phys Rev B 73 (2006): 214305. 10.1103/PhysRevB.73.214305 2006