TION wileyonlinelibrary. com Adv. Mater. 2012, 24, 523–527 eliminated. This requires post acquisition processing of multiple images recorded under varying imaging conditions. Here, we used the through-focal series reconstruction method in which the exit wave is reconstructed from a set of images taken at different defocus values.[26] The present observations relate to a (110) type twin boundary formed in the orthorhombic Pnma CaTiO3 phase after cooling from the cubic high temperature phase [17] and imaged along its [001] zone-axis in order to maximize the visibility of any expected atomic displacements. The imaging conditions are schematized in Figure 1, also noting the respective definitions for the further discussion. The experimental focal series comprised 20 images separated by a focal increment of–2.4 nm with the series centred around the zero defocus condition (starting defocus+ 27 nm) with a spherical aberration coefficient of+ 50 µm (see the Experimental Section for a full list of experimental parameters). The actual reconstruction of the exit wave is carried out using the TrueImage software. After reconstruction the residual aberrations are corrected using the standard techniques in TrueImage. The amplitude and phase of the reconstructed exit wave are shown in Figure 2a and b, respectively, with a resolution equal to 0.8 Å. An example of a low-magnification image of the relevant area is given in the Supporting Information (Figure S1) including a fast Fourier transform (FFT) revealing the spot splitting confirming the twin nature of the interface. Although the combination of exit wave reconstruction with aberration-corrected TEM significantly improves the visual interpretability, quantitative numbers for the atomic column positions are still lacking. Therefore, techniques such as statistical parameter estimation theory need to be included in order to properly interpret the experimental data. This allows position measurements of all atomic columns with a precision of a few picometers without being restricted by the information limit of the microscope.[23, 24, 27–29] For a further quantitative analysis we will use the phase of the reconstructed exit wave since it is directly proportional to the projected electrostatic potential of the structure. First, the atomic column positions are estimated using statistical parameter estimation theory.[24] Therefore, a local region of the reconstructed phase including the twin wall has been analysed. This region is indicated by the rectangular box in Figure 2b. The estimated atomic positions are shown as an overlay in Figure 3a. Next, the projected