• thermal expansion;
  • cuprite structure;
  • Cu2O;
  • Ag2O.

The thermal expansion of two isostructural oxides, Cu2O and Ag2O, has been measured from 10 K to their respective decomposition temperatures by means of high-resolution X-ray powder diffraction. The thermal behaviours of the two oxides are different. Cuprite has a negative thermal expansion up to about 200 K, and above this temperature it becomes positive. Ag2O, on the other hand, has a negative thermal expansion up to its decomposition temperature. A comparison with EXAFS data in the same temperature range shows that the observed difference between the thermal expansion regimes of the two compounds can be ascribed to the vibrational behaviour of the Cu and Ag atoms and, in the ultimate analysis, to the different rigidities of the metal–oxygen bonds.