Negative thermal expansion and local dynamics in Cu{sub 2}O and Ag{sub 2}O

Journal Article · Thu Jun 01 04:00:00 EDT 2006 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.73.2· OSTI ID:20788207

Sanson, A; Rocca, F; Dalba, G; Fornasini, P; Grisenti, R; Dapiaggi, M; Artioli, G ^[1]

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1. IFN, Istituto di Fotonica e Nanotecnologie del Consiglio Nazionale delle Ricerche, Sezione CeFSA di Trento-38050 Povo (Trento) (Italy)

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}O and Ag{sub 2}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}O, up to 470 K for Ag{sub 2}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.

• OSTI ID: 20788207
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 21 Vol. 73; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
ANISOTROPY
BOND LENGTHS
COPPER OXIDES
CRYSTALS
FINE STRUCTURE
LATTICE PARAMETERS
OXYGEN
SILVER OXIDES
TEMPERATURE DEPENDENCE
THERMAL EXPANSION
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY