Stress adaptation in ceramic thin films.

Two mechanisms by which an inorganic thin film may reversibly adapt to externally imposed strain have been considered: (1) the chemical strain effect and (2) self-organization of polycrystalline macro-domains. The chemical strain effect is due to the transformation of the elastic energy of an externally applied stress into chemical energy of interacting point defects. This effect may be observed in solids with a large concentration of interacting point defects if the interaction is accompanied by a large change in specific volume. Self-organization of polycrystalline macro-domains may take place when single-domain ferroelastic grains minimize intergrain strain via approximate mutual alignment of their crystallographic axes. Each such macro-domain region has a preferred size and direction of alignment. In the presence of externally applied stress, these regions may reorganize, thereby partially converting the elastic energy of the external stress into the elastic energy of intergrain stress. Although very different in nature, both mechanisms result in reversible strain-relaxation. The conditions under which each of these effects may be present are understood well enough to provide clear guidance for preparation of materials and for their incorporation into practical devices.