Considerations for BaTiO₃ Ceramics with High Piezoelectric Properties Fabricated by Microwave Sintering Method

A decrease in the domain size of barium titanate (BaTiO 3 ) improves the piezoelectric constant ( d 33 ). Other considerations suggest the high d 33 of BaTiO 3 may be caused by the enhanced high dielectric constant ( ε 33 T / ε 0 ) at room temperature due to the size effect. However, we have clarified that even a sample with a low ε 33 T / ε 0 shows high d 33 according to the optimization of microwave sintering conditions. We have verified that the d 33 of BaTiO 3 ceramics fabricated by microwave sintering is as high as 370 pC/N despite the ε 33 T / ε 0 of 2100. Mechanisms affecting d 33 in microwave sintering and in conventional sintering of BaTiO 3 are thought to be different. The relationship between the grain size, the mechanical quality factor Q m , and the frequency constant N p , which was obtained from microwave sintering, has assumed that a decrease in grain size causes a decrease in internal stress. We suggest that a decrease in internal stress induces continuity of strain in a grain boundary, resulting in continuity of domains across a grain boundary.