Bipolar strain hysteresis of poled composites with Nd-Mn-doped PZT fibres

Nd-Mn-doped PZT fibres were produced using the sol-gel process. The PZT was doped with 2 mol% neodymium and an amount of 1.1 mol% or 0.75 mol% manganese. The fibres were investigated with respect to microstructure, composition after sintering and phase content. Strain and polarisation were measured after imbedding the fibres in a polymer matrix. The resulting 1-3-composites were poled with constant electric field. Measurements of strain and polarisation were done using a sinusoidal voltage of high amplitude. Instead of a shifted strain hysteresis (butterfly loop) an asymmetric strain-field relation was observed. The asymmetry depends on the direction of the applied voltage. For the half wave with voltage parallel to former poling voltage the strain curve is linear. For the other half wave the strain curve inflates and there is a region with no change of strain. Possible explanations for the asymmetric strain behaviour are discussed.