EXAFS and XRD Study of Local Dynamics in Cu2O and Ag2O

Copper and silver oxide share the rather unusual cuprite structure,formed by two interpenetrating networks of corner-sharing M4O tetrahedra (M=Cu,Ag).Negative thermal expansion of the cell parameter has been observed from 5 to about 200 K for Cu2O and up to 470 K for Ag2O by powder diffraction.In the case of Ag2O, it has been shown by EXAFS that the lattice contraction is accompanied by an expansion of the Ag-O distance and that the deformation of the Ag4O tetrahedral is not negligible.In this work we present a comparison between EXAFS and XRD results for both compounds. The comparison between local and lattice thermal expansions,measured by EXAFS and XRD,respectively,and the differences found between the two compounds,allow to gain original insight on the mechanism of negative thermal expansion in framework structures