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Abstract

The elastic behavior of solids with a large concentration of
interacting point defects has been analyzed. The analysis predicts
that, in such solids, mechanical stress may be partially relieved by a
shift in the association/dissociation equilibrium of the point defects.
Association/dissociation of the point defects in response to an
external stress will proceed until the decrease in elastic energy is
balanced by the increased chemical energy of the defect distribution.
The resulting change in the linear dimensions may be called "chemical
strain", in analogy to the previously studied "chemical stress". A
solid in which chemical strain may develop in response to external
stress should exhibit two distinct Young's moduli: relaxed, on a time
scale which allows the defects to reach equilibrium; and unrelaxed, on
a time scale which is too short for the defect equilibrium to be
established. Our analysis suggests that materials exhibiting the
chemical-strain effect are capable of reversible adaptation to external
mechanical constraints. Measurements on a self supported film of
Ce0.8Gd0.2O1.9 strongly support the theoretical predictions.