PHASE-EQUILIBRIA IN THE ND2-XCEXCUO4 SYSTEM LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.6)

The Nd-Ce-Cu-O phase diagram has been examined in the Nd2CuO4 - CeO2 p seudobinary section, with the aim to find out the equilibria that lead to the formation of the Nd1.85Ce0.15CuO4-delta superconducting phase, in the Nd2-xCexCuO4 solid solution (alpha phase), in the compositiona l range x = 0.0 divided by 0.6. The limit of extension of the alpha so lid solution at room temperature appeared very restricted; it consider ably increases over 1000 degrees C and it reaches the maximum value (x = 0.25) at T = 1200 degrees C (in air). Our results display solid sol ution (and in particular the superconducting phase) to be a non equili brium phase at room temperature.