Crystal Chemistry and Phase Equilibrium Studies of the BaO(BaCO ₃ )–½R ₂ O ₃ –CuO x Systems in Air: VI, R = Neodymium

Crystal chemistry and subsolidus phase equilibrium studies of the Ba‐Nd‐Cu‐O system near the CuO and Nd 2 O 3 corners have been carried cut at 950°C in air. Two solid‐solution series have been identified in the Ba‐Nd‐Cu‐O system. The first series involves the high‐ T c superconductor phase, and has the formula Ba 2–x Nd 1+x Cu 3 O 6+z , where × < ≅ 0.7. At the ideal compound stoichiometry of Ba 2 NdCu 3 O 6+z , the transformation from the high‐ T c orthorhombic to tetragonal phase occurs at 550°–575°C in air. This temperature varies as a function of composition, and at x ≅ 0.2 to 0.3 it occurs at 950°C. The second solid solution is the non‐superconducting “brown phase” represented by Ba 2+2x ‐Nd 4–2x Cu 2–x O 10–2z 0 ≤ x ≤ 0.1. Preliminary phase diagrams of the BaO–Nd 2 O 3 and Nd 2 O 3 –CuO x systems are also presented. Standard X‐ray diffraction patterns of BaNd 2 –CuO 5 and (Nd 1.9 Ca 0.1 )CuO 4–z are provided.