Local thermal expansion in a cuprite structure: the case of Ag2O

The local thermal behavior of the Ag2O 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 Ag4O basic tetrahedral units. Accordingly, the negative thermal expansion of the lattice parameter in Ag2O cannot be explained uniquely in terms of rigid unit modes.