Characterization of superconductingBi2Sr2Can−1CunO4+2nphases withFe57Mössbauer spectroscopy

In order to study the dependence of superconductivity on sample preparation and the influence of cationic doping, ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$ ${\mathrm{Cu}}_{\mathit{n}}$ ${\mathrm{O}}_{4+2\mathit{n}}$ samples were prepared using various sintering temperatures and nominal starting compositions. After each sintering the samples were characterized with x-ray-diffraction and magnetic-ac-susceptibility measurements. In all cases the corresponding ${}_{}{}^{57}{}_{}{}^{}\mathrm{doped}$ samples were also made for Mössbauer measurements. The Mössbauer measurements usually show three quadrupole components arising from the different phases in the samples. The site assignment of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ is discussed.