EXAFS and local thermal expansion: the case of silver oxide.

Temperature dependent extended X-ray absorption fine structure (EXAFS) measurements give original information on local structure and dynamics of materials with framework structure, exhibiting negative thermal expansion. By proper cumulant data analyses, the temperature dependence of the nearest neighbours distance can be directly measured and the degree of rigidity of basic structural units monitored. Recent results obtained for Ag2O show that the contraction of the lattice parameter is accompanied by the expansion of the 1st-shell Ag-O distance, and that the deformation of the Ag4O tetrahedral units is not negligible