There are mainly two classes of ferroelectric phase transitions: displacive (e.g. BaTiO₃) and order-disorder (e.g. NaNO₂). For displacive ferroelectrics, for instance, Jia et al. [1, 2] observed the distributions of polarizations of Pb(Zr,Ti)O₃ (PZT) in an atomic scale with aberration-corrected transmission electron microscopy (TEM). They proposed that the polarizations were formed with the atomic displacements of about 30 pm.

[1] C. L. Jia, S. B. Mi, K. Urban, I. Vrejoiu, M. Alexe, and D. Hesse, Nature Mater. 7, 57–61 (2008).
[2] C. L. Jia, K. W. Urban, M. Alexe, D. Hesse, and I. Vrejoiu, Science 331, 1420–1423 (2011).