Phase equilibrium in Eu–Ba–Cu–O system

We have reinvestigated the phase diagram of the Eu–Ba–Cu–O system at 950°C in the pertinent regions of its isobaric–isothermal sections, both in air and in pure oxygen, i.e., at 0.2 and 1.0 atm oxygen pressure. The results show that there is an equilibrium quadrilateral (with O 2 as the fifth phase) which is composed of the 123, 211, 011 and 143 phases (at a specified oxygen pressure). At higher temperatures, a diagonal tie-line exists between the 123 and 143 phases rather than between the 211 and 011 phase. At temperatures lower than the 5-phase equilibrium the tie-line connects the 211 and 011 phases. The equilibria change as a function of temperature has been studied hereby, and the resulting modification of the Eu–Ba–Cu–O phase diagram as a function of temperature and O 2 pressure is reported. The observed new high-temperature phase relationship allows the “143” phase to be considered instead of 011 as a possible pinning center in 123. This may have important implications with respect to raising the critical current density, J c, of the EuBa 2Cu 3O 7− δ high- T c superconductor.