Annealing and structure studies on Tl-2223 and Tl-1223 crystals

摘要

Single crystals with nominal stoichiometry Tl2Ca2Ba2Cu3O10 (Tl-2223) and TlCa2Ba2Cu3O9 (Tl-1223) have been annealed in flowing oxygen or nitrogen and the complete crystal structure determined by least-squares refinement of Mo K(alpha) x-ray diffraction data. Small atomic displacements are found after the anneals that are consistent with a model in which small amounts of Tl(sup 1+) present in the Tl-O layer are subsequently reversibly oxidized/reduced during mild oxygen/nitrogen anneals to Tl(sup 3+). Despite substantial changes in oxygen content in the Tl-O layers with annealing, Meissner data show very modest shifts in the superconducting transition temperature, suggesting little change in the carrier concentration in the Cu-O(sub 2) planes. 2 refs.