Direct study of nucleation and domain-wall motion in ferroelectric triglycine sulphate

The pyroelectric probe technique is now capable of visualizing details as small as 1 μm in a ferroelectric triglycine sulphate (TGS) crystal. Following observations are made: 1. There is a specific microscopic domain texture in a virgin TGS crystal. 2. Wall motion in a TGS crystal is directly observed for the first time during the course of investigation. Walls do not move smoothly. They often leave nonswitched, or partially switched microsopic domains, which need several minutes to reverse after the bulk crystal. These irregularities lead probably to the well-known Barkhausen pulses which are observed during, and sometime after wall motions. The average wall velocity, v, depends on electric field, E, according an exponential law: v = v∞ e−δ/E with a limiting value v∞ = 4750 mm/s, and an activation field δ = 1.15 MV/m for a plate thickness e = 20 μm. 3. There is a distribution of nucleation field values in the crystal. 4. The distribution of the nucleation field values depends on the wall motion history of the crystal. This distribution can be modified with a suitable electric treatment. 5. For very thin films the equation for the wall velocity has to be replaced by v = v0 eαE which has also been used for ferromagnetic films. At room temperature v0 = 10−6 mm/s is independent on thickness e, while α is increasing with e.