The crystal structure of the superconductor HgBa2Ca2Cu3O8+δ with Pb substitution

Pb-doped Hg1-xPbxBa2Ca2Cu3O8+δ superconductors with x=0.0 to 0.50 and increment steps of 0.1 have been synthesized. For x=0.30, the sample has the highest superconducting transition temperature, TcR=0 135 K (the zero-resistance temperature), and Tconset = 143 K (the diamagnetic onset temperature) (results given by Shao H M, Lam C C, Fung P C W, Wu X S, Du J H, Shen G J, Chow J C L, Ho S L, Hung K C and Yao X X 1995 Physica C 246 207). The crystal structures of these solid solutions have been investigated by synchrotron x-ray diffraction (SXRD) and Raman spectroscopy at room temperature. The lattice parameters decrease with the increase of the content of Pb. From SXRD refinements, one of the most significant features of this study is that there are great differences between some of the cation-oxygen bond distances - such as the (Hg/Pb) - O bond distance - of Pb-free and Pb-doped samples. The impurity phases appearing in our samples are CaHgO2 and BaCuO2, which are refined together. The content of each phase is determined from the refined scale factor. Raman studies show that the peaks appearing at 232 cm-1, 671 cm-1, and 632 cm-1 are due to the impurity phase, and four peaks at the frequencies of 107 cm-1, 477 cm-1, 577 cm-1 and 597 cm-1 are due to the vibrations of oxygen atoms in the superconducting phase. No Raman peak shift is observed when the laser irradiation power is changed. (author)