Determination of crystal point group by a high-resolution electron microscope image

Crystal symmetry is exposed in a high-resolution electron microscope image more clearly at the thick part than at the thin part of the crystal, through the dynamical scattering. The crystal point group can be determined by observing how the symmetry in the image changes with thickness. A proposed method is demonstrated with an example of a bismuth titanate, Bi₇Ti₄NbO₂₁.