Cell parameters refinements showing an influence of the chemical nature ofthe grain surface on the crystalline characteristics of fine grained powders

The evolution of the cristalline state of fine grained BaTiO3 powders has b een investigated by X-ray diffraction during desorption - adsorption cycles in order to study the effect of the chemical nature of the surface of fine grains on their internal crystalline structure. A weak but significant inc rease in the cell parameter has been observed after adsorption of water on a nanometric BaTiO3 powder, showing that the physico-chemical interactions between the solid and the adsorbent are responsible for a tension state in the material. Similar evolution has been previously observed on nanometric MgO powders;this phenomenon can be generalized to all kind of fine grained materials.