New Hg based oxycarbonate superconductor HgBa 2Sr 2Cu 2O 6+ δ(CO 3)

Abstract

A new Hg based oxycarbonate superconductor HgBa 2Sr 2Cu 2O 6+ δ (CO 3) has been found by resistivity and magnetization measurements. The superconductivity has been observed at 66 K by magnetization measurement. The electron-diffraction and HRTEM studies show that the crystal structure basically consisted of [HgBa 2O 2+ δ ] and [Sr 2CO 3] block layers and has a tetragonal unit cell, with a=3.88 A ̊ , c=16.94 A ̊ , with an orthorhombic superstructure, with A≈4.5√2a=24.71 A ̊ ,B≈√2a=5.49 A ̊ , C=c=16.94 A ̊ , due to the three times periodic replacements of a CO 3 block for HgO δ in the same c-planes or to a c/2 shift approximately at intervals of three tetragonal cells along the (110) direction. The crystal structure of this compound is described by the following combination: [(Hg 0.5C 0.5)(Ba,Sr) 2O 2.5+ δ ]+CuO 2+[(Ba,Sr) 2(C 0.5Hg 0.5)O 2.5+ δ ]+CuO 2.