Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LRE) form a solid solution LRE1+xBa2-xCu3O7+delta (LRE123ss), with increasing substitution of the LRE3+ for the Ba2+ as the ionic radii of the LRE increases. The range of solubility is, for any given LRE system, strongly dependent on the oxygen partial pressure (PO2) and may be temperature dependent. Nd123ss is of particular interest due to the development of a process for making melt textured material with exceptionally high pinning from this material. From the point of view of superconductivity, the upper end of the subsolidus solid solution is not of particular interest for Nd123ss. However the lower end of the solid solution exhibits a significant dependence on both PO2 and temperature. Under the conditions used in melt texturing these changes should lead to the precipitation of second phases which will pin flux.