Electron-doped infinite-layer Sr1-xLnxCuO2 superconductors: synthesis, magnetism, and transport

We report the results of SQUID magnetization, x-ray diffraction, and transport studies of polycrystalline specimens of the electron-doped infinite-layer compounds Sr1-xLnxCuO2 (Ln = lanthanide element, x 0-0.16). Samples are synthesized at high pressure (25 kbar), typically at temperatures in the range 950-1085 C. X-ray diffraction data indicate that the solid solution phase boundary occurs at x ∼ 0.10, somewhat lower than previously supposed. Magnetic and superconducting properties are a sensitive function of synthesis conditions, with optimal superconducting behavior (-4πχ ∼ 0.6-0.9) observed for a very narrow (∼10 C) synthesis window. Only a small variation of Tc (Tc ∼ 43 K) with dopant ion size is observed; a smaller Tc for Ln = Gd may imply an appreciable rare-earth ion-conduction electron exchange coupling, J ∼ 11 meV. (orig.)