Cation distribution in the superconducting Tl, Pb-1223 phase (“Tl 0.5Pb 0.5Sr 2Ca 2Cu 3O 9”) from resonant synchrotron powder X-ray diffraction

Abstract

The cation distribution in a polycrystalline sample of nominal composition “Tl 0.5Pb 0.5Sr 2Ca 2Cu 3O 9” with T c = 118 K has been determined from resonant synchrotron X-ray diffraction data collected at the Cu K, Tl L III, Pl L III and Sr K edges. Cation disorder is found at all the non-copper sites according to the formula ( Tl 1− x Pb x ) ( Sr 2− y Ca y ) ( Ca 2− z Tl z ) Cu 3 O 9 where x = 0.53(2), y = 0.42(2) and z = 0.064(4) for our sample. The overall composition Tl 0.53Pb 0.53Sr 1.58Ca 2.36Cu 3O 9 confirms that an excess of Ca and a deficiency of Sr can stabilise the Tl, Pb-1223 structure.