First-principles calculation of the optical properties of the YBa₂Cu₃O_7- oxygen vacancies model

We used first-principles methods to investigate how oxygen vacancy defects affect the optical properties of YBa₂Cu₃O_7- (0 < δ < 1), a high-temperature superconductor with potential applications in optical detectors. We calculated the electronic structure of YBa₂Cu₃O_7- with different amounts of oxygen vacancies at three different sites: Cu-O chains, CuO₂ planes, and apical oxygens. The formation energy calculations support the formation of oxygen vacancies in the Cu-O chain at higher concentrations of vacancy defects, with a preference for alignment in the same chain. The presence of oxygen vacancies affects the optical absorption peak of YBa₂Cu₃O_7- in different ways depending on their location and concentration. The optical absorption peaks in the visible range (1.6-3.2 eV) decrease in intensity and shift towards the infrared spectrum as oxygen vacancies increase. We demonstrate that oxygen vacancies can be used as a powerful tool to manipulate the optical response of YBa₂Cu₃O_7- to different wavelengths in optical detector devices.