Comparison of superconductivity-depression for lanthanum and potassium replacing barium in YBa2Cu3Oy ceramic cuprate

The nominal composition of YBa2-xKxCu3Oy (YBKCO) cuprates with x less than or equal to 0.50 has been synthesized by the standard solid state reaction technique. X-ray diffraction (XRD) and the resistivity measurements are used to characterize the structure and the superconductivity of YBKCO cuprates. There was no impurity phase detected with x less than or equal to 0.20. The structure of the main phase ("123") is orthorhombic with Pmmm symmetry in the whole doping range. With increasing potassium content, the lattice constants and some other structural parameters are almost unchanged. The refined potassium content is consistent with that of the nominal one. The zero resistance temperature T-c0 decreases sharply with the increase of potassium content in YBKCO as x less than or equal to 0.20, and is almost unchanged as x > 0.20. We compared these results with those of La-doped YBa2-zLaxCu3Oy cuprates. The difference in superconductivity depression may result from the shift oxygen which transfer conducting carriers from Cu(1)-O chains to Cu(2)-O-2 sheets. (C) 2000 Elsevier Science B.V. All rights reserved.