HIGH-PRESSURE SYNTHESIS OF CUBA2CAN-1CUNOX (N = 3, 4) SUPERCONDUCTORSWITHOUT EXTERNAL OXIDIZING-AGENTS

We have successfully synthesized non-stoichiometric BaCuO2+delta as a precursor for the high-pressure synthesis of CuBa2Can- 1Cu(n)O(x) [Cu- 12(n - 1)n] superconductors. The oxygen content of BaCuO2+delta was de termined by a coulometric titration method. Using this precursor but n o external oxidizing agents, samples which were superconducting with T -c=116 K have been obtained by sintering at 1100 degrees C under 5 GPa . The T-c = 116 K phase was identified to be the CuBa2Ca3Cu4Ox (Cu-123 4) phase. The Meissner volume fraction of the sample was estimated at ca. 30% at 5 K. A sample which contained a superconducting phase with T-c at 80 K was also obtained at a temperature as low as 950 degrees C . The 80 K phase was identified to be the CuBa2Ca2Cu3Ox (Cu-1223) phas e. Thus, the Cu-1234 and Cu-1223 phases were successfully synthesized without the presence of any external oxidizing agents. (C) 1998 Elsevi er Science S.A. All rights reserved.