Aging effects in pure and doped barium titanate ceramics

Ferroelectric properties of 9% mol (Hf,Zr)-doped BaTiO₃ ceramics have been studied by comparison with those of pure tetragonal BaTiO₃ ceramics. The addition of doping ions lead to a shift of the rhombohedral to orthorhombic and orthorhombic to tetragonal transition temperatures above 0°C, and to a decrease of tetragonal to cubic (ferroelectric to paraelectric) transition temperature from 122°C to 95°C on heating and from 120°C to 85°C on cooling. In pure tetragonal ceramics at room temperature, aging develops by a thermally activated process, leading to a linear dependence of the relative permittivity and dielectric loss on the logarithm of time. In the case of doped ceramics, the experiments showed a decreasing reversed-S dependence of capacitance and tan δ on the logarithm of time, suggesting that dielectric aging in these materials is related with defect diffusion. It was concluded that in doped BaTiO₃ ceramics the aging mechanisms depend on the crystalline symmetry, which influences the twinning process and the domain-wall dynamics. Aging of (Hf,Zr)-doped BaTiO₃ ceramics depends on temperature and the phase symmetry, which imposes the twinning rate and the rearrangement speed of ferroelectric domains minimizing the elastic energy of the lattice