Phase stability of cuprate superconductors with the composition NdBa2Cu3Oz

The phase stability of the high-temperature superconductor Nd1+xBa2-xCu3Oz, which has been manufactured from highly homogeneous precursors, is examine d over a wide temperature range from 600 to 1100 degrees C. The phase of th e stoichiometric cationic composition NdBa2Cu3Oz (x = 0), which has the hig hest superconducting transition temperature of T-c= 94 K, can exist only at about 985 degrees C (P-O2 = 12 280 Pa). At higher or lower temperatures, s olid solutions with x = 0.05-0.1 are stable. As a consequence, the low-temp erature oxidation of the NdBa2Cu3Oz phase (600 degrees C, oxygen) can resul t in solid-state decomposition to produce barium cuprates and in a substant ial decrease in T-c. At temperatures between 1060 and 1080 degrees C, parti al melting and growth of whisker crystals occur.