Space charge and polarization in PETP at different temperatures

PETP (polyethyleneterephthalate) samples were poled at constant voltage and at different temperatures. Charge injection and orientation of dipoles as a function of the poling time at temperatures above 60°C were measured with the PPS method under short circuit conditions. At room temperature the temporal injection and migration of space charges were observed. After long poling times a characteristic distribution of charges was observed. For temperatures above 60°C, a strong additional orientation of dipoles in the field direction was observed. In cooling down to room temperature under field the dipoles remained oriented with strong piezoelectricity of the film. A few days later the injected space charges in excess of dipole compensation vanished. Most of the dipoles remained oriented for several months