Contrasting aging behavior of as-grown and annealed BaTiO3 single crystals grown by KF-flux technique

Acceptor-doped ferroelectrics generally show a pronounced aging effect. However, the KF-flux-grown BaTiO3 single crystals, which are known to contain acceptor impurities K+, show no aging effect. This exception poses a potential challenge to the current understanding of ferroelectric aging and may provide a clue for reducing aging effect in acceptor-doped ferroelectrics. To solve this puzzle, we compared the ferroelectric and dielectric aging effects of the as-grown and annealed KF-flux-grown BaTiO3 single crystals. We found that although the as-grown BaTiO3 showed almost no aging effect, the annealed BaTiO3 showed clear aging effect. Chemical analysis revealed that 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 contain mostly K+, as a result of F- evaporation. Based on defect chemistry analysis and the microscopic mechanism of the aging, the difference in the aging behavior of the two kinds of crystal is fully explained. Our result suggests that besides the thermodynamic driving force due to the symmetry-conforming short-range ordering of point defects, kinetic factors (the mobility of point defects) also play a crucial role in determining whether or not aging appears. Donor doping is an effective way to reduce the aging effect through eliminating mobile oxygen vacancies. (c) 2007 American Institute of Physics.