In situ synchrotron X-ray studies of epitaxial SrCoO_x heterostructures

The reversible topotactic phase transition in strontium cobaltite (SrCoO_x) thin films, controlled by oxygen stoichiometry, holds significant potential for neuromorphic and ionotronic devices. Here transition between the brownmillerite (BM) SrCoO_2.5, an insulating antiferromagnet, and the perovskite (PV) SrCoO₃, a ferromagnetic metal, can be precisely manipulated by varying the oxygen concentration. Despite extensive research into their magnetic and electronic properties, the kinetics and dynamics of oxygen vacancy ordering under different thermal and environmental conditions remain inadequately understood.



In this study, we utilize in situ coherent X-ray scattering at the Advanced Photon Source to monitor the phase evolution and vacancy dynamics of epitaxial SrCoO_x thin films grown on (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7(001) (LSAT) substrates under alternating O₂ and N₂ atmospheres. We study the kinetics of the phase transition from 300ºC to 360ºC, noting distinct behaviors when switching between oxidized and reduced phases. The vacancy ordering kinetics are compared to X-ray Absorption Near Edge Structure (XANES) measurements conducted at the Co K-edge, demonstrating the distinction between oxygen vacancy injection and vacancy ordering. We compare our results with those from films grown on SrTiO₃(STO) substrates, illustrating the influence of epitaxial strain on the phase transition.