NONSTOICHIOMETRY AND DECOMPOSITION OF LA1+ZBA2-ZCU3OY AND LA4BACU5O13-W

The temperature (T, K) and oxygen pressure (p(O2), Pa) dependence of oxygen content in La1+zBa2-zCu3Oy (123) and La4BaCu5O13-w (415) were determined over the ranges 10 Pa to 0.1 MPa O2, 0.0 less-than-or-equal-to z less-than-or-equal-to 0.7 and 523 less-than-or-equal-to T less-than-or-equal-to 1223 K. The data for each phase were correlated with chemical thermodynamic representations. For La1+zBa2-zCu3Oy, the T-z-y-p(O2) behavior was modeled as a solution of LaBa2Cu3O7-x and 415. The experimental data demonstrated 7-x values < 6 at high temperatures, while they exceeded 6.99 only at temperatures approaching ambient at 0.1 MPa O2. These two characteristics are not known to occur in the other lanthanide and Y analogues. The T-z-p(O2) dependence of high-temperature decomposition was determined and, in conjunction with X-ray analysis, permitted construction of the phase diagram lying between LaBa2Cu3O7-x and 415. Effects of residual carbonate content were also determined.