Preparation of Hg0.8Cr0.2Ba2CuO4+delta under controlled oxygen and mercurypartial pressures

Ba2CuO3/HgBa2CuO4+delta and Mn3O4/Mn2O3 couples were employed to control th e mercury and oxygen partial pressures, respectively, during the synthesis of chromium doped Hg-1201 phase in the sealed quartz tube. Suitably adjuste d conditions allowed us to prepare series of single phase samples of the fi nal composition Hg0.7Cr0.2Ba2CuO4+delta determined by weight changes and EM A. The oxygen stoichiometry was modified by the oxygen partial pressure in the range of pO(2) = 0.05-1.59 atm. The X-ray diffraction and magnetic susc eptibility study revealed linear dependence of the structural parameters an d parabolic one of T-c vs. log pO(2). Multiphase samples, however, form for too high oxygen activity, namely for pO(2) = 5.16 atm. (C) 1999 Elsevier S cience B.V. All rights reserved.