Structure refinement of infinite-layer superlattices

The structure of (BaCuO2)(2)/(CaCuO2)(2) superconducting superlattices (SLs), obtained by the pulsed-laser deposition technique, was investigated by X-ray diffraction (XRD) and X-ray specular reflectivity (XSR). Simulations of XRD and XSR data obtained by varying the structure factor and, consequently, the chemical composition of the hypothesized structure lead to an accurate structural determination of the investigated SLs. For the (BaCuO2)(2), layers of the investigated superconducting SLs we found that the copper-to-barium ratio obtained by the simulations is less than one. Moreover, the copper vacancies are localized only in the CuO2 planes between barium atoms. Nonstoichiometric compounds with an excess of oxygen are compatible with the experimental data, indicating the Ba2Cu2-xO4-y layers to be the 'reservoir charge blocks' in the superconducting SLs.