Stress-strain behavior during compression of polycrystalline La1-xCaCoO3 ceramics

Mechanical stress-strain behavior of LaCoO3, La0.8Ca0.2CoO3 and La0.7Ca0.3CoO3 was studied under compression at 25C and 300C. A hysteresis in the stress-strain relationship due to reorientation of ferroelastic domains (deformation twins) was observed, and a remanent strain is measured after unloading. The cohersive stress, defined as the maximum in effective elastic compliance during first loading, increases with substitution of Ca for La and decreases with increasing temperature. Domain reorientation was confirmed by X-ray diffraction of surfaces parallel and perpendicular to the loading direction. LaCoO3 can be regarded as a soft ferroelastic material while the 30 % Ca substituted material is a hard ferroelastic. The hysteresis of the stress-strain relationship was clearly dependent on both composition and temperature.