Direct observation of apical oxygen vacancies in the high-temperature superconductor YBa2Cu3O7−x
Steven T. Hartman, Bernat Mundet, Juan-Carlos Idrobo, Xavier Obradors, Teresa Puig, Jaume Gázquez, Rohan Mishra
DOI 10.1103/PhysRevMaterials.3.114806 · Physical Review Materials
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Abstract
The properties of the high-temperature superconductor YBa2Cu3O7−x (YBCO) depend on the concentration of oxygen vacancies (VO). It is generally agreed upon that VO form in the CuO chains, even at low concentrations where the critical temperature for superconductivity peaks (x≈0.07), with only a handful of reports suggesting the presence of VO at the apical sites. In this paper, we show direct evidence of apical VO in optimally doped YBCO samples. Using density-functional-theory calculations, we predict that isolated VO are equally favorable to form in either the CuO chains or the apical sites, which we confirm using atomic-resolution scanning transmission electron microscope imaging and spectroscopy. We further show that apical VO lead to significant lattice distortions and changes in the electronic structure of YBCO, indicating they should be considered on an equal footing with chain VO to understand the superconducting properties of YBCO in the optimal doping region.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| YBa2Cu3O7-x Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 92 | Pressure not reported | onset |
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