H. Bao, National Institute for Materials Science, Tsukuba, 305-0047, Ibaraki, Japan, Tsukuba, Japan; L. Zhang, Xi’an Jiaotong University, Xi’an, 710049, China, Xi'an, China; Y. Wang, National institute for Materials Science, Japan, Tsukuba, Japan; W. Liu, National Institute for Materials Science, Tsukuba, Japan; X. Ren, National Institute for Materials Science, Tuskuba, Japan
Generally, shape-memory materials refer to the martensitic alloys that can remember the original shape on changing temperature or stress. Recently a larger recoverable electro-shape-memory effect is reported in piezoelectrics based on the new symmetry-conforming principle of point defects. Such a shape memory effect in piezoelectrics is due to the aging effect which is induced by acceptor dopants. However, the KF-flux-grown BaTiO3 single crystals, which are known to contain acceptor impurities K+, show no aging effect. There has been no explanation for this exception. To solve this puzzle, we compared the ferroelectric and dielectric aging effect of as-grown and annealed KF-flux-grown BaTiO3 single crystals, and found the as-grown BaTiO3 showed almost no aging behavior, but the annealed BaTiO3 showed clear aging effect. Chemical analysis revealed that such a difference is related to their difference in composition: the as-grown crystals contain not only acceptor impurity K+, but also higher concentration of anion donor F-; on the other hand, the annealed crystals mostly K+ as a result of F- evaporation. Based on a defect chemistry analysis and the microscopic mechanism of the aging, the aging behavior of the two kinds of crystal can be fully explained. Our result suggests that oxygen vacancy, rather than acceptor dopant, is the crucial factor for determining whether or not the aging effect exists.
Summary: based on the study on the aging properties of electro-shape-memory materials K doped BaTiO3 and KF doped BaTiO3, we prove that oxygen vacancy, rather than acceptor dopant, is the crucial factor for determining whether or not the aging effect exists.
