TEM study of phases and domains in NaNbO3 at room temperature

It is found with TEM that there is a new phase, called M phase, coexisting with the normal P and Q phases at room temperature. All kinds of ferroelectric domains in the Q phase and antiferroelectric domains in the P phase are observed. They are in good agreement with the results given by the symmetry theory on domains and domain wall orientations in the ordered phase. Translation domain walls (TDWs) are also observed in the P phase as well as in the Q phase. The translation vector was determined as [100]p (here p means pseudocubic unit cell). In addition, the effect of translation domain walls on electron diffraction is reported and interpreted theoretically. It is concluded that NaNbO3 (NN) is a heterogeneus system both in phases and in domains at room temperature.