Depolarisation of PZT thin films by nanoindentation

The electromechanical properties of lead zirconate titanate (PZT) sol-gel processed thin films with different thickness (70 and 700 nm) have been investigated by nanoindentation. Using conductive (WC/Co) spherical indenters with different radii (100 μm and 500 μm) the current intensity transients were recorded during indentation loading. The depolarisation of non-poled (but self-polarised) and poled films was measured. For the 700 nm, non-poled film the effective self-polarisation was 0.030 C/m². Indentation of the 700 nm film with the 500 μm radius indenter produced highly reversible electric displacements. This enabled us to estimate an effective indentation piezoelectric coefficient, which ranged from 39 to 45 pC/N. The depolarisation appears to be associated with the mechanical stress induced movement of non-180° ferroelectric domain walls. The charge transients at the peak load have different relaxation times, which suggests that the structure and/or environment of the ferroelectric walls is different in the surface and bottom electrode regions of the films.