Neutron powder diffraction and magnetic properties of Pb-0212

Several cuprates of type Pb-0212 are prepared. The crystal structure is refined from neutron powder diffraction and X-ray diffraction data as tetragonal (space group 14/mmm). Interestingly, Pb is simultaneously present in two atomic positions with CN 8 and 9 and considered as Pb4+ and Pb2+. Superconductivity with Tc between 30 and 75 K is observed in the system Pb0.5La1.5-xSr1+xCu2Oy. However, in as-prepared powdered materials the superconducting volume fraction remains low due to the formation of grain boundaries acting as weak links, whereas a significant improvement is obtained in bulk materials by use of flux. Moessbauer and susceptibility measurements of Fe substituted materials indicate the development of a spin glass like behaviour at low temperatures. (orig.)