Cation distribution in Hg sites of (Hg,Pb)-1223 determined by synchrotron X-ray anomalous scattering

Abstract

Site occupancy of Hg, Pb and Cu atoms in the Hg sites of (Hg,Pb)(Ba,Sr) 2Ca 2Cu 3O 8+ δ has been determined by means of two-wavelength anomalous dispersion (TWAD) method. Synchrotron X-ray diffraction experiments were performed for a single crystal in four-circle diffractometry at wavelengths of 1.3906 and 1.0191 Å, which are 0.01 Å longer than Cu K and Hg L III absorption edges, respectively. With sin θ/ λ-independent anomalous scattering factors, the TWAD method is indispensable for determining the cation distribution accurately in a ternary system involving three cations. It is concluded that there is no substitution of copper on the Hg sites. Both mercury and lead occupy the Hg sites in the ratio of Hg:Pb=0.4:0.6(1). The substitutions of lead in the Hg sites and strontium in the Ba sites are sensitive to interatomic distances of Hg–O(3) and Cu(2)–O(3), respectively.