Rhenium effect in the formation and stability of HgCaO2 and Hg1-xRexBa2Ca2Cu3O8+delta superconductor

Using a novel technique (thermobaric analysis or TEA) to measure in situ th e pressure in quartz tubes, we have investigated the influence of Hg and Re -x content in the range 0.00 less than or equal to x less than or equal to 0.25 on the formation and stability of HgCaO2. Moreover the competition bet ween the synthesis of HgCaO2 and of the superconductor Hg1-xRexBa2Ca2Cu3O8delta (Hg,Re)-1223 was investigated. The pressure determination has enabled us to obtain all thermodynamic parameters such as the enthalpy Delta H-d(0 ), entropy Delta S-d(0) and the Gibbs free energy Delta (d)G(0) and follow the decomposition reactions by monitoring the pressure behavior. This possi bility of pressure measurements has also allowed us to acquire a better kno wledge on the effects of Re substitution in the formation of(Hg,Re)-1223. T he TEA technique has also permitted us to minimize the HgCaO2 impurity cont ent and hence to improve the quality of the ceramic (Hg,Re)-1223 supercondu ctor. (C) 2001 Elsevier Science B.V. All rights reserved.