Study of the negative thermal expansion of cuprite-type structures by means of temperature-dependent pair distribution function analysis: preliminary results

Copper (I) and silver (I) oxides crystallize with the same structure, and both show a wide range of negative thermal expansion (NTE): Cu2O contracts with temperature up to about 200 K and then expands, while Ag2O has a NTE up to its decomposition temperature at about 450 K. Here we report a careful temperature-dependent pair distribution function (PDF) analysis that showed that copper oxide, at about 200 K, exhibits geometric distortions of the tetrahedral units, probably related to a change in the solid angle of the polyhedra. Silver oxide, on the other hand, showed the same distortions even at the lowest temperature measured (10 K): structural refinements of the PDF confirmed the presence of local distortions (below 10A˚ ) at all temperatures.