Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films

Abstract

The ability to manipulate oxygen anion defects rather than metal cations in complex oxides is facilitating new functionalities critical for emerging energy and device technologies.However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of an important defect, oxygen vacancies. Here, strontium cobaltite (SrCoO x ) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 °C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by ~30%, resulting in a tunable oxygen deficient steady-state under conditions that would normally fully oxidize unstrained cobaltite. These strain-induced changes in oxygen stoichiometry drive the cobaltite from a ferromagnetic metal towards an antiferromagnetic insulator. The ability to decouple the oxygen vacancy concentration from its typical dependence on the operational environment is useful for effectively designing oxides materials with a specific oxygen stoichiometry.2

Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo2O5.5+δ Thin Films

“…Moreover, a larger number of oxygen vacancies formatted in the LBCO films will induce the increase of c -axis lattice parameter, which is in agreement with our RSM measurements31323334.…”

Strain control of oxygen kinetics in the Ruddlesden-Popper oxide La1.85Sr0.15CuO4

“…Although the thermodynamics of defect formation could also play a role in the differences observed between the two strain states, the formation energy differences for the two favorable defects (i.e., peroxide interstitials and equatorial vacancies) in each case were very small, only on the order of 100 meV. Thus, a lower defect formation energy cannot be the dominant cause of the large differences in oxygen stoichiometry between compressive-strained and tensile-strained films observed in this work, although such changes may be dominant in perovskites 15, 16, 31 .…”

Equilibrium oxygen storage capacity of ultrathin CeO2-δ depends non-monotonically on large biaxial strain

“…showed that strained La 0.5 Sr 0.5 CoO 3–δ thin films undergo cation ordering (unlike the bulk oxide), facilitated by lower oxygen vacancy formation energy and enhanced cation mobility under biaxial strain. Another recent ex situ study of strained SrCoO 3-δ observed an increase in oxygen nonstoichiometry with tensile strain41, though the non-equilibrium nature of the experiment convolutes the kinetics and thermodynamics of oxygen vacancy formation. As can be seen, the difficulty of isolating strain effect from that of the buried interface and misfit dislocations, and the lack of in situ measurements, have precluded a clear connection between biaxial strain and oxygen storage capacity.…”