Origin of fatigue in ferroelectric perovskite oxides

We calculated the electronic states of ferroelectric perovskite oxides, ATiO(3), using the discrete variational X alpha cluster method. The bond order of the pi bonds between Ti 3d and O 2p as a function of titanium ion displacement in PbTiO3 shows a maximum. This result suggests that the magnitude of ferroelectricity is related to the magnitude of the pi bonds. We also found that the occupancy of s electrons in A ions increases the strength of pi bonds between a titanium ion and oxygen ions. This result also suggests that the magnitude of ferroelectricity is related to the magnitude of the pi bonds. Therefore, we propose that the appearance of oxygen vacancies is one of the origins of fatigue in PZT because the pi bonds between a titanium ion and oxygen ions are weakened by remaining electrons of oxygen vacancies.