The melting and dissolution processes of solute (Nd0.33Eu0.33Gd0.33)Ba2Cu3Ox (referred to as NEG123) and flux Ba3Cu10O13 were in situ observed, both in air and 0-1% O-2 in Ar, using high-temperature optical microscopy, and phase diagrams were constructed. The range of liquidus line was found to be narrower in 0.1% O-2 in Ar ambient as compared to that in air. Plate-like NEG123 single crystals (average crystal size 3.6 x 3.2 x 0.3mm(3)) were grown by freezing method. A superconducting onset transition temperature of similar to90 K was obtained for oxygen-annealed crystals. (C) 2002 Elsevier Science B.V. All rights reserved.