Valence changes and structural distortions in "charge ordered" manganites quantified by atomic-scale scanning transmission electron microscopy

We investigate the microscopic nature of the "charge ordering" modulation in mixed-valent manganites in real space using scanning transmission electron microscopy. The modulation in Bi0.5Sr0.4Ca0.1MnO3 has a uniform periodicity appearing as stripes in high angle annular dark field images. Geometric phase analysis shows the modulation to be a displacement wave with transverse amplitude (0.008+/-0.001)a and longitudinal amplitude (0.003+/-0.001)a. Series of energy loss spectra taken across the stripes show no periodic changes and place an upper bound of +/-0.04 on any valence changes of the Mn ions.