Elasticity of Solids with a Large Concentration of Point Defects II. the Chemical Strain Effect in Ce_0.8Gd_0.2O_1.9

The chemical strain effect describes a mechanism of stress relaxation in solids that can be attributed to the conversion of elastic energy into chemical energy of point defects. Experimental confirmation of this effect is presented here for the case of thin self-supported films of the ionic conductor Ce _0.8Gd_0.2O_1.9. If heated slowly, (<5°C min^-1) these films remain flat within the temperature range of 25-180°C. If heated more rapidly than ∼ 20°C min^-1, the films buckle above 53°C, but after ∼ 3-30 min at elevated temperatures, they become flat again, demonstrating that stress-relaxation has taken place. The degree of stress reduction observed is consistent with the value calculated for this system using Boltzmann statistics in the case of small strain. These findings confirm the concept of stress adaptability in solids that we introduced in Part I and suggest that a large class of such materials, which exhibit the chemical strain effect, is likely to be found.