Topotactic lattice healing: A post-growth strategy for eliminating persistent oxygen vacancies in La0.67Sr0.33MnO3 films

Oxygen vacancies in complex oxide films often obscure intrinsic physics and degrade functional performance. Here, we report a post-growth defect-healing strategy via sequential vacuum/oxygen annealing. This process drives a reversible perovskite–brownmillerite topotactic phase transition, effectively eliminating persistent oxygen vacancies that survive conventional thermal annealing. Using La0.67Sr0.33MnO3−δ films as a model system, we validate this strategy on both SrTiO3 and LaAlO3 substrates. Following this defect-healing treatment, the lattice parameters converge to their theoretical stoichiometric values, yielding substantially enhanced physical properties: the metal–insulator transition temperature (TMI) approaches its bulk value; the remanent magnetization increases by nearly an order of magnitude; and the saturation magnetization (Ms) more than doubles at room temperature. With the restored stoichiometry, the intrinsic effects of strain can be directly observed without interference from oxygen vacancies. Structurally, the films on SrTiO3 and LaAlO3 exhibit distinct strain-relaxation behaviors—spatially distributed vs interface-confined relaxation. In transport, TMI exhibits a weaker dependence on substrate strain than in the conventionally annealed states. Moreover, the magnetic and transport responses exhibit opposite substrate dependences: TMI and conductivity are lower on LaAlO3 than on SrTiO3, whereas the room-temperature Ms is higher, pointing to distinct microscopic channels of strain control. These results demonstrate that this topotactic phase transition strategy provides clean material platforms for developing high-quality oxide devices and exploring intrinsic strain physics in perovskite oxides.