Phase diagram of the Y-Ba-Cu-O system

The phase diagram of the four-component system Y-Ba-Cu-O is investigated under 'artificial' air with Ar + 21 percent O2, avoiding the CO2 pollution from the atmosphere. Three isothermal sections at 1263 K, 1223 K and 1173 K are precisely determined. The phase diagram is essentially composed of four three-component oxides, i.e., the superconducting 123 phase as well as the 211, 143 and 163 phases. From the temperature dependence of the phase relations, seven univariant reactions are experimentally clarified, where four condensed phases coexist in equilibrium. The univariant reaction temperatures are determined thermoanalytically. Based on these experimental data, a reaction scheme for univariant reactions is proposed for the whole system, where eight additional hypothetical univariant reactions are suggested to exist. Two temperature-concentration sections crossing the 123 superconducting phase are estimated.