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.