Synthesis of Epitaxially Strained Brownmillerite Strontium Cobaltate (SrCoO$_{2.5})$

Strontium cobaltate (SrCoO$_{3})$ is a perovskite oxide predicted to have metal-insulator transitions and magnetic phases induced by epitaxial strain. The related brownmillerite phase SrCoO$_{2.5}$ has a similar structure, but contains alternating planes of oxygen vacancies in the octahedral oxygen cages of the perovskite structure. We demonstrate epitaxial growth of SrCoO$_{2.5}$ on both SrTiO$_{3}$ and LaAlO$_{3}$ substrates by molecular beam epitaxy using RF oxygen plasma. X-ray diffraction measurements show finite thickness oscillations that are characteristic of smooth films, and half-order diffraction peaks that are representative of the brownmillerite phase. We observe a single tetragonal domain when the film is deposited on SrTiO$_{3}$ with the planes of oxygen vacancies parallel to the interface. When grown on LaAlO$_{3}$, the film contains multiple orthorhombic domains. We conclude that the observed domain structures for SrCoO$_{3}$ grown on SrTiO$_{3}$ and LaAlO$_{3}$ are due to ordering of the oxygen vacancies to reduce strain. We will also present strategies to increase the oxygen content to that of SrCoO$_{3}$.