Thermodynamic calculation of yttrium-barium-copper-oxygen phase diagram

International Science Foundation Long-Term Research Grants Program

Principal Investigator Name and Address
Gennady Fedorovich Voronin
Chemistry Department
Moscow State University
119899 Moscow

V.A. Lysenko
E.B. Rudnyi
I.A. Zaitseva

Grant Number MRL 000

In 1994, the new results as follows below have been obtained in accordance with the plan of the project:

  1. The subsolidus equilibria in the mixture yttrium-barium-copper-oxygen including the metastable states of superconductor phases have been computed.

    Fig. 1. Stability fields of the 123 phase. This phase is thermodynamically stable between the bold lines 1-5. The lines 1-7 represent decomposition reactions according to equations (1-7).

  2. The phase equilibria and thermodynamic values for the subsystems of copper-yttrium, barium-yttrium, copper-barium-yttrium, yttrium-oxygen including all the intermediate phases, solid and liquid solutions have been evaluated ("optimized").

    Fig 2. Solidus and liquidus of Y-O system.

    Fig. 3. Phase diagram of the Ba-Cu.

    Fig. 4. Phase diagram of the Cu-Y.

    Fig. 5. Phase diagram of the Ba-Cu-Y at 1273 K.

  3. The method for estimating thermodynamic functions in homologous series of compounds have been developed and, after that, the thermodynamic properties of the hypothetical high temperature superconductors, Y2Ba4Cu9O17 and YBa2Cu5O9 have been estimated. From here, the conditions (temperature, oxygen pressure and composition) when these two phases can be synthesized have been predicted.

    Fig. 6. Phase diagram of the system YBa2Cu3O6+z + CuO at 1 atm of oxygen pressure

  4. The thermodynamic models and auxiliary values to calculate other subsystems and the complete quaternary yttrium-barium-copper-oxygen system have been prepared.