Fig. 2: Time and spatially resolved X-ray diffraction of the electroforming process.

a Optical microscope images during an electrical forming process on a BCFO thin-film device prepared with a 1 mm-wide gap between the coplanar electrodes. b Position-dependent X-ray diffraction performed after completion of the electroforming process. The color scale indicates the diffraction intensity normalized by the monitor count of the incident X-ray beam. The blue mark represents the near-electrode area wherein oxygen vacancies accumulate, but it is observed that the c-axis lattice parameter is not significantly changed from the as-grown state value (not shown here due to ion milling outside the electrode region). The red mark corresponds to the electrically formed region where oxygen vacancies are depleted, resulting in the contraction of the c-axis lattice parameter. The black mark indicates the SrTiO₃ substrate. c Time-dependent L values of the film and substrate peaks around the (002) reflection. The reciprocal lattice unit is defined as 2π/3.905 Å. d Real-time current between the electrodes. Two anomalies in the time derivative of the current clearly indicate the phase transitions. e Time-dependent variations of the c-axis lattice parameters for the initial/intermediate tetragonal phase (blue) and the electrically formed emergent monoclinic phase (red). f Areal ratio of the superlattice peak to the primary diffraction peak