High-pressure synthesis of (Cu,C)(Ba,Y) 2YCu 2O z and (Cu,C)Sr 2(Y,Sr)Cu 2O z

Abstract

Cupric oxides (BaY) 2YCu 3− x C x O z (C-213) and (Cu 1− x C x )Sr 2(R,Sr)Cu 2O z (R  Y or Ho; C-1212) have been synthesized under various oxygen pressures. Its composition, structure and superconductivity are investigated. Two kinds of C-213 phases have been crystallized depending on carbon content oxygen pressdure. One of them is excessin copper, Cu = 3.03–3.16, while the other phase is deficient in copper and barium, Cu ≈ 2.8 and Ba ⩽ 1.91 per formula unit. The copper-excess composition for the former phase is due to intergrowths of double CuO chains. The latter phase crystallized only under high oxygen pressures. The phase transition from orthorhombic to tetragonal structures takes place by increasing the carbon content in the C-213 phase. All C-213 cuprates exhibit superconductivity below ≈ 92 K when they are adequately oxidized. Sr analogues of (Ba,Y) 2YCu 3− x C x O z ( x ⩾ 0.1) cannot be synthesized. Moreover, none of the C-1212 phases examined exhibit bulk superconductivity in spite of the oxygenation at high pressures of oxygen.