Electronic phase separation is known to occur in complex oxides ranging from high-Tc superconductors to colossal magnetoresisitive (CMR) manganites. Accumulating experimental evidences show regions of temperature dependent conducting and insulating regions, whose exact origin is unknown. Theoretically, it is has been shown that these systems are unstable from the strong interplay between the lattice, charge and spin degrees of freedom.

The key to understand the electronic phase separation in complex oxides is the structure. Electron diffraction is the only probe that covers the length scales from angstroms to microns. Characterization at these length scales is critical (electronic phase separations are typically about nanometers in sizes). Traditionally, electron diffraction has been played important roles in discovering the new types of phase separations, but has contributed little to the quantitative understanding. The reason is the strong interaction of electrons with matter, which gives both strong inelastic background and multiple scattering.