We report on the direct observation of apical oxygen vacancies (VO) in optimally doped YBa2Cu3O7-x films by HR-STEM. DFT calculations evidence that isolated apical and chain VO have similar formation energy, for low vacancy concentrations. Also, apical VO significantly distorts the surrounding lattice and the electronic structure of YBCO. An influence to the superconducting properties is suggested.

Direct observation of apical oxygen vacancies in the high-temperature superconductor YBa2Cu3O7x
Steven T. Hartman, Bernat Mundet, Juan-Carlos Idrobo, Xavier Obradors, Teresa Puig, Jaume Gázquez, Rohan Mishra
Physical Review Materials 3, 114806, 2019
DOI: 10.1103/PhysRevMaterials.3.114806

Figure: (a) The atomic structure of fully oxygenated YBa2Cu3O7-x. The locations of the three possible oxygen vacancies are marked. (b) ABF image with its contrast inverted to show the atomic columns as bright spots. (c) Panel showing two horizontal intensity profiles measured along the BaO planes showing different concentration of VO. (d) The orbital-projected DOS of the superconducting CuO2 plane with Cu atom directly adjacent to an apical vacancy. The planar Cu 3dz2 states are in gold.

 

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