Thermodynamic properties of HgBa2CuO4+δ

Thermodynamic propel-ties of the HgBa2CuO4+delta superconductor with different extra oxygen (delta) content and Ba2CuO3.05 were investigated by a method of solution calorimetry. The formation enthalpy values of HgBa2CuO4+delta from oxides (HgO, BaO and CuO) for different delta were obtained (-102.0+/-3.3 kJ/mole for delta=0.02, -113.3+/-3.2 kJ/mole for delta=0.08; -116.8+/-3.1 kJ/mole for delta=0.11). The obtained data show that the HgBa2CuO4+delta superconductor is thermodynamically stable at room temperature with regard to decomposition into Ba2CuO3.05 and mercury oxide. Moreover, its oxidation by oxygen decreases significantly the formation enthalpy, and, therefore, should take place in the studied range of delta variation. (C) 1999 Elsevier Science S.A. All rights reserved.