Relaxation of induced polar state in relaxor PbMg_1/3Nb_2/3O₃ thin films studied by piezoresponse force microscopy

Polarization state in epitaxial thin films of relaxor ferroelectric PbMg_1/3Nb_2/3O₃ (PMN) was experimentally studied at the nanoscale using a piezoresponse force microscopy (PFM). In the absence of a dc bias applied to the PFM tip, no piezoelectric activity could be found on most of the surface of the film. Under a moderate voltage (≫1.5–2 V), a polar state with a nonzero piezoresponse could be induced. Longer poling resulted in a significant reduction of the initial piezoresponse. After removing the bias field, a long-term relaxation of the piezoelectric signal obeying a Kohlrausch-Williams-Watt dependence was observed.