A method for forming a heterostructure includes forming a first perovskite crystal structure complex oxide material layer over a substrate to a first thickness. A second perovskite crystal structure oxygen deficient complex oxide oxygen getter material layer is formed upon the first perovskite crystal structure complex oxide material layer. When the second perovskite crystal structure oxygen deficient complex oxide oxygen getter material layer reaches a critical thickness that may approximate one-half to one times the first thickness, the first perovskite crystal structure complex oxide material layer spontaneously transforms into a first brownmillerite crystal structure complex oxide material layer, with an attendant transfer of substantially one-half oxygen atom per perovskite unit cell to the second perovskite crystal structure oxygen deficient complex oxide oxygen getter material layer, thus forming a second perovskite crystal structure oxygen enriched complex oxide oxygen getter material layer. A particular heterostructure derives from the foregoing methodology.