Hole filling and hole creation in the superconducting compounds Bi2Sr2-xRxCuO6+y (R=La, Pr, Nd, and Sm)

The superconducting properties, hole content, and lattice constants of several rare-earth-doped compounds Bi2Sr2-xRxCuO6+y have been investigated as a function of rare-earth doping and oxygen content. The maximum superconducting transition temperature, Tc, obtained for each of the rare-earth dopants was 23 K (La), 25 K (Pr), 21 K (Nd), and 12 K (Sm). The Tc's of these compounds exhibited a parabolic dependence on the La and Pr concentration (00.2, the samples were single phase and exhibited unusually sharp superconducting transitions (width of ac-susceptibility transition less than 2 K). The high quality of the samples allowed a precise study of the variation of the orthorhombic cell parameters with the rare-earth and oxygen content