In oxidizing conditions, a negative space charge potential is induced at the surface, which results in a repulsive interaction with Ni dopants of relative negative charge compared to the host cations. The magnitude of the space charge potential decreases with decreasing oxygen activity, that is, under reducing conditions, and allows for the exsolution of Ni to the surface region, which serves as a sink of Ni dopants forming metallic nanoparticles. In consequence, a concentration gradient of Ni dopants evolves, which further promotes the exsolution of dopants to the surface. At highly reducing conditions, an inversion of the SCR towards a positive surface potential may promote the exsolution of dopants by attractive electrostatic interactions. The presence of near-surface SCRs is strongly entangled with the surface redox chemistry of the perovskite host lattice and widely dictates the exsolution kinetics. The electrostatic gradient of the SCR, critical for the release of dopants to the perovskite surface, is mainly determined by oxygen activity and temperature during thermal treatment.
