A recent transmission electron microscopy (TEM) method using precession electron diffraction (PED) was used to obtain LiFePO 4 and FePO 4 phase mapping at the nanometer-scale level on a large number of particles of sizes between 50 and 300 nm in a partially charged cathode. Despite the similarity of the two phases (the difference of lattice parameters is <5%), the method gives clear results that have been confirmed using high-resolution transmission electron microscopy (HRTEM) and energy-filtered transmission electron microscopy/electron energy loss spectroscopy (EFTEM/EELS) experiments. The PED maps show that the particles are either fully lithiated or fully delithiated and, therefore, bring a strong support to the domino-cascade model at the nanoscale level (scale of a particle). A coreÀshell model or spinodal decomposition at mesoscale (scale of agglomerates of particles) is possible. Size effects on the transformation are also discussed.

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A computer program called ARPGE written in Python uses the theoretical results generated by the computer program GenOVa to automatically reconstruct the parent grains from electron backscatter diffraction data obtained on phase transition materials with or without residual parent phase. The misorientations between daughter grains are identified with operators, the daughter grains are identified with indexed variants, the orientations of the parent grains are determined, and some statistics on the variants and operators are established. Some examples with martensitic transformations in iron and titanium alloys were treated. Variant selection phenomena were revealed.