Role of Sr doping and external strain on relieving bottleneck of oxygen diffusion in La2-xSrxCuO4-δ

In many complex oxides, the oxygen vacancy formation is a promising route to modify the material properties such as a superconductivity and an oxygen diffusivity. Cation substitutions and external strain have been utilized to control the concentration and diffusion of oxygen vacancies, but the mechanisms behind the controls are not fully understood. Using first-principles calculations, we find how Sr doping and external strain greatly enhances the diffusivity of oxygen vacancies in La2-xSrxCuO4-delta (LSCO) in the atomic level. In hole-doped case (2x > delta), the formation energy of an apical vacancy in the LaO layer is larger than its equatorial counterpart by 0.2 eV that the bottleneck of diffusion process is for oxygen vacancies to escape equatorial sites. Such an energy difference can be reduced and even reversed by either small strain (< 1.5%) or short-range attraction between Sr and oxygen vacancy, and in turn, the oxygen diffusivity is greatly enhanced. For fully compensated hole case (2x <= delta), the formation energy of an apical vacancy becomes too high that most oxygen vacancies cannot move but would be trapped at equatorial sites. From our electronic structure analysis, we found that the contrasting change in the formation energy by Sr doping and external strain is originated from the different localization natures of electron carrier from both types of oxygen vacancies.

Automated summary

In many complex oxides, the formation of oxygen vacancies can be a promising method to modify material properties. This study investigates the effects of Sr doping and external strain on the diffusivity of oxygen vacancies in LSCO. The calculations reveal that Sr doping and strain can greatly enhance the diffusivity by reducing the energy barrier for oxygen vacancies to escape from equatorial sites. However, in the case of fully compensated holes, the formation energy of apical vacancies becomes too high, leading to the trapping of most oxygen vacancies at equatorial sites.