DOPANT SOLUBILITY, PHASE-STABILITY AND SUPERCONDUCTIVITY IN SR-DOPED LA2-XSRXCACU2O6

We report the synthesis and characterization of the Sr-doped cuprate s uperconductor La2-xSrxCaCu2O6 (326) for doping levels ranging from x=0 to 0.35. Powder neutron diffraction studies of these sample show that single-phase Sr-doped 326 is obtained only within the narrow range: 0 .05 < x < 0.2 with the synthetic conditions used. At low values of x, La2-ySryCuO4 (214) is produced and the 326 material is Ca rich. At hig her values of x, it becomes progressively more difficult to produce th e 326 phase and both La8-zSrzCu8O20 (z almost-equal-to 1.9) and CaO ap pear as extra phases. Although it is not possible to refine the La/Sr ratio in samples with x=0.30 and 0.35, structural changes with doping suggest that additional Sr continues to be incorporated. The observed changes in superconducting behavior with doping are discussed in terms of structural changes, the role of the interstitial oxygens, and chan ges in the hole concentration.