ALKALINE-EARTH DOPING IN LANTHANUM NEODYMIUM CALCIUM CUPRATES WITH THE 212-STRUCTURE

The solid solutions La1-xNdSrxCaCu2Oy (0 less-than-or-equal-to x less-than-or-equal-to 0.6) and La1-xNdCa1+xCu2Oy (0 less-than-or-equal-to x less-than-or-equal-to 0.5) were synthesised by conventional solid state reaction methods. All compounds were subsequently annealed at high oxygen pressures (almost-equal-to 450atm). Both series of materials have been characterised by powder x-ray diffraction and oxygen stoichiometries for unannealed and high pressure annealed samples were determined by thermogravimetric analysis. Structures of two of the unannealed calcium doped series (x=0 and x=0.4) were determined by Rietveld analysis of powder x-ray diffraction data. Structural studies showed low oxygen levels, y < 6, and that the O3 site between Cu-O planes is vacant. The structures also showed increasing Cu-Cu interplanar distance with increasing calcium content. Resistivity measurements showed no superconducting transitions in these materials. Structural aspects of these and other 212 phases are discussed in relation to the observation or absence of superconducting behaviour.