Effect of the Phase Transformation on the Fracture Behavior of BaTiO ₃

The fracture energy of BaTiO ₃ increased with increasing grain size at 25°C in the ferroelectric 4 mm symmetry state and remained constant at 150°C in the paraelectric m 3 m state. In general, observed flaw sizes agreed with those predicted from fracture mechanics equations. The fracture energy measurements combined with previously reported strength measurements were analyzed in terms of fracture mechanics principles to determine the effect of internal stresses on fracture. The analysis showed that the effect of internal stress on fracture for a given flaw size can be determined from a combination of fracture energy and strength measurements at two temperatures. The increase in fracture energy with grain size in the ferroelectric state is attributed to ferroelastic twin formation and wall motion.