Effect of Internal Stress on the Strength of BaTiO 3

The strength of BaTiO 3 which had been hot‐pressed to ∼99% of theoretical density and tested above the Curie temperature was—9000 psi greater than at room temperature. This measured difference in strength is attributed to internal stress from the cubic→tetragonal phase transformation. Correction of measured strength to zero porosity predicts internal stresses of ∼11,000 psi, in good agreement with the dielectric theory for fine‐grain BaTiO 3 . The internal stress is nearly independent of grain size in the range ∼1.5 to 150 μm, showing that 90° domains do not reduce internal stresses causing failure. Lower internal stress in commercial BaTiO 3 is attributed to greater porosity, large flaw sizes, and possibly the effects of additives.