Polarities of ferroelectric 180° domains observed using scanning electron microscopy and a liquid toner method in an uncoated triglycine sulfate crystal

Both scanning electron microscopy and a liquid toner method have been carried out on an identical uncoated b plate of triglycine sulfate (TGS), to clarify the correspondence between the polarities of ferroelectric 180° domains and the contrast of their secondary electron images (SEI). It has been found that the contrast between the ends of adjacent 180° domains is reversed in a toner pattern, as well as in an SEI, between two temperature regions above and below the aging temperature Ta. This is attributed to the change in the sign of the total surface charge density σt at Ta, which consists of spontaneous polarization Ps and true charge density σn on the ends of adjacent domains. The magnitude of σn, which exactly neutralizes Ps at Ta, remains almost unchanged while the magnitude of Ps increases with decreasing temperature. Negatively charged toner particles are adsorbed on the end with σt≳0 of each domain, which corresponds to the (+) domain of Ps≳0 below Ta and the (−) domain of Ps<0 above Ta. It has been determined, on the basis of the above sign of Ps, that the end with σt<0 of each domain is observed to be bright in the SEI, which corresponds to the (−) domain below Ta and the (+) domain above Ta. Electric fields generated both inside and outside the TGS plate can contribute to the secondary electron emission from the end with σt<0 of each 180° domain.