Direct measurement and interpretation of electrostatic potentials at 24° [001] tilt boundaries in undoped and niobium-doped strontium titanate bicrystals

Phase contrast techniques in the transmission electron microscope are used to measure electrostatic potentials at 24 degrees [001] tilt boundaries in nominally undoped and Nb-doped SrTiO3 bicrystals, All of the boundaries are found to have lower scattering potentials than the surrounding bulk crystal. Origins for the measured changes in potential are investigated through the application of high-resolution transmission electron microscopy, diffuse dark-field imaging, energy dispersive X-ray spectroscopy, and parallel electron energy loss spectroscopy. Significantly, we show that space charge is not the dominant contribution to the potential because the magnitudes of the potentials seen cannot be explained on the basis of ionic space charge theory alone.