Local thermal expansion in a cuprite structure: the case of Ag(2)O.

The local thermal behavior of the Ag(2)O framework structure has been studied by extended x-ray absorption fine structure. The average Ag-O nearest-neighbor distance expands upon heating, while the Ag-Ag next-nearest-neighbor distance contracts. An original implementation of the cumulant analysis shows that the Ag-O expansion is a joint effect of potential anharmonicity and geometrical deformation of the Ag(4)O basic tetrahedral units. Accordingly, the negative thermal expansion of the lattice parameter in Ag(2)O cannot be explained uniquely in terms of rigid unit modes.