Platinum-assisted phase transition in bismuth-based layer-structured ferroelectric CaBi4Ti4O15 thin films

The phase transition of nonferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depends on platinum bottom electrodes. Rather than the strain and crystallinity of the bottom electrode, matching of the atomic arrangement to the Ca-Bi-Ti-O thin films is predominant. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650 deg. C showed c-axis orientation. In contrast, thin films crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore grains which were about several tens of nanometers in diameter and located in the interface region. They showed P-V hysteresis loops. The remanent polarization and coercive electric field depended on platinum top electrode size