Figure 9

Fourier analysis of the HRTEM image in the [110] orientation. (a) unprocessed HRTEM image and (b) fast Fourier transform of HRTEM image. The frequencies marked with red circles describe the Pm − 3m symmetry. The weak frequencies marked with green circles are caused by the Fm − 3m ordering in the lattice. Areas depicted in (e) and (f) are Fourier filtered images using only the frequencies from the Pm − 3m symmetry and with additional Fm − 3m frequencies, respectively. The areas are taken from the position marked by the red box in the HRTEM image. (c) and (g) are differential images subtracting the Pm − 3m from the Fm − 3m filtered images. Areas with clear two-dimensional periodicity can be used to estimate the domain size with the Fm − 3m symmetry.