Thermochemical investigation of YBa_2Cu_3O_(7-δ) superconductor doped by lutetium

摘要

The synthesis of Y_(0.72)Lu_(0.28)Ba_2Cu_3O_(6.91) has been performed by solid-state reaction from Y_2O_3, Lu_2O_3, BaCO_3 and CuO. The X-ray measurements confirmed the orthorhombic structure (space group is Pmmm). For the first time the standard molar enthalpy of formation of Y_(0.72)Lu_(0.28)Ba_2Cu_3O_(6.91) has been determined by solution calorimetry combining the enthalpies of dissolution of Y_(0.72)Lu_(0.28)Ba_2Cu_3O_(6.91) in 2 M HC1 and literature data. It is found out that at room temperature this complex oxide is thermodynamically stable with respect to a decomposition into binary oxides or a mixture of individual phases (YBa_2Cu_3O_(6.91) and LuBa_2Cu_3O_(6.91)). It could be established that substitution of Lu increases the stability of the Y123 phase.