In order to reduce the sintering temperature and enhance the piezoelasticity, a small amount of CuO was added into BaTiO3 during sintering. The aging behaviour of these CuO modified BaTiO3 ceramics was studied systematically. For unpoled ceramic, the P-E loop changes gradually from a normal single-loop curve to a double-loop with aging. Meanwhile, the S-E loop develops gradually from a normal strain curve to one with almost zero strain under electric field below 10kVmm-1. For poled ceramic, it builds a much stronger and more stable internal bias after aging. The P-E loops shift significantly along the electric field and the strain loop shows high asymmetry with one side of high linearity. A dipolar defect model was proposed to explain these aging behaviours. The defect dipoles consisting of Cu2+ occupying B site and oxygen vacancy can re-orientate gradually with time to align with the spontaneous polarisation. Then, the aligned defect dipoles could provide a strong restoring force on the domain wall motion and thus lead to all the observed aging behaviours.
