NEUTRON POWDER DIFFRACTION AND MAGNETIC-PROPERTIES OF PB-0212

Several cuprates of type Pb-0212 are prepared. The crystal structure i s refined from neutron powder diffraction and X-ray diffraction data a s 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 T-c 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 signific ant improvement is obtained in bulk materials by use of flux. Mossbaue r and susceptibility measurements of Fe substituted materials indicate the development of a spin glass like behaviour at low temperatures.