Substitution studies on copper oxide systems

Four different metal oxide systems having the formulas La2CuO4, Ba2YCu3O6+x, Ca0.85Sr0.15CuO2, and Cu4O3 were prepared at ambient or high pressure using solid state reactions of the appropriate binary oxides. Substitution reactions were performed on these systems in order to examine the structural effects. These substituted products were also examined for superconducting behavior. The critical temperature and magnetic susceptibility were determined for those compounds exhibiting superconducting properties. Fluorine substitution for oxygen in the lanthanum-copper-oxide system produced a superconductor with a critical temperature of 37 K and the formula: La2Cu2+1-yCu3+y O4+zFx (where x = 0.15). The magnetic susceptibility data indicated a broad transition to superconductivity at 37 K with the Meissner fraction in the range of one percent. The electrical resistivity data also indicated the formation of a superconductor at the same critical temperature. The substitution of open-quotes didymiumclose quotes (a mixture of praseodymium, neodymium, cerium and lanthanum) for yttrium in the Ba-Y-Cu-O system, produced superconductors with critical temperatures of 37 K and 55 K, dependent upon the source and composition of the open-quotes didymiumclose quotes oxide. The decrease in the critical temperature from 92 K in Ba2YCu3O6+x was probably caused by site preference of the cations, oxygen vacancies, and/or electronic and chain decoupling