Selective formation of apical oxygen vacancies in La2-xSrxCuO4

The superconducting properties of high-T-c materials are functions of the concentration of charge carriers, which is controlled by the concentration of defects including heterovalent cations, interstitial oxygen ions, and oxygen vacancies. Here we combine low-temperature thermal treatment of La2-xSrxCuO4 epitaxial thin films and confocal Raman spectroscopy to control and investigate oxygen vacancies. We demonstrate that the apical site is the most favorable position to accommodate oxygen vacancies under low-temperature annealing conditions. Additionally we show that in high-quality films of overdoped La2-xSrxCuO4, oxygen vacancies strongly deform the oxygen environment around the copper ions. This observation is consistent with previous defect-chemical studies, and calls for further investigation of the defect-induced properties in the overdoped regime of the hole-doped lanthanum cuprates.