Time-dependent space-charge-limited conduction as a possible origin of the polarization offsets observed in compositionally graded ferroelectric films

The effects of free space charges on hysteresis-loop measurement of compositionally graded ferroelectrics were investigated. These effects were quite likely to be responsible for the polarization offsets observed in experiments. An expression for the conduction-current density associated with those free space charges was also derived. The computer simulation of compositionally graded lead zirconate titanate, which was placed in the Sawyer-Tower circuit and driven by an alternating applied voltage, produced shifting of measured hysteresis loops.