Bulk synthesis of Ln 1− xCa xBa 2Cu 4O 8 (Ln = Y, Ho) by the oxygen-hip technique

Abstract

The synthesis conditions of Ca-doped Ln 1 − x Ca x Ba 2Cu 4O 8 (Ln = Y, Ho) under high pressure oxygen are investigated. The process which goes through the 1-2-3 phase shows a low superconducting volume fraction of 35%, but the direct process which does not go through the 1-2-3 phase showed a high superconducting volume fraction of 95% in both Y and Ho compounds. The maximum volume fraction is obtained at a Ca concentration of x = 0.1. With increasing Ca-substitution, T c increases to 90 K and remains constant for x ∥#62; 0.1. The critical current density, J c = 5.6 × 10 4 A/cm 2, and Anderson's thermal activation energy, U = 2.1 × 10 -2eV, are estimated at T = 4.3 K and H = 1 T from M-H hysteresis curve measurements and the time dependence of remanent magnetization measurements, respectively.