Inhomogeneous crystallinity and its influence on piezoelectricity of Bi12TiO20-BaTiO3 polar composites fabricated by thermal gradient sintering

We have previously described the enhancement of piezoelectricity in low crystallinity Bi12TiO20–BaTiO3 (BTO-BT) nanocomposites. This poses a question regarding the effect of the crystallinity on piezoelectricity. Here, the variation of crystallinity and structure that was developed along the temperature gradient was confirmed. The magnitude of the piezoelectric constant was found to have great relationship with the crystallinity and distortion of BiO5 polyhedra of amorphous Bi12TiO20. The highest piezoelectric constant of 13pC/N was obtained together with the lowest crystallinity and highest degree of distortion of BiO5 polyhedra. These results highlight the key role of the amorphous phase and further confirm the importance of distortion of BiO5 polyhedra in influencing the piezoelectricity. In this view, one may also expect that macroscopic polarity could be improved by increasing the amorphous content and the degree distortion of the BiO5 bonding units in the system.