Cation distribution and composition of the Tl-2223 superconductor from combined powder neutron and resonant X-ray diffraction

Abstract

A combined powder neutron and resonant X-ray diffraction study of a post-annealed Tl-2223 (“Tl 2Ba 2Ca 2Cu 3O 10”) superconductor with T c(0)=124.5 K shows that Cu substitutes for Tl in the TlO layers and Tl substitutes at the Ca sites. The resulting composition is (Tl 1.72Cu 0.28)Ba 2(Ca 1.86Tl 0.14)Cu 3O 10, and some indications of how the stoichiometry of Tl2223 varies with starting composition have been obtained. Using excess Cu in the synthesis of Tl2223 gives more phase-pure material than other starting compositions, resulting in a T c=127 K sample after only 3.5 h synthesis time.