Phase decomposition and structural defects in a Y-Ba-Cu-O superconductor

Phase decomposition of a bulk Y2Ba4Cu 8O16 superconductor has been studied. The microstructure of the sample is heavily faulted and contains many stacking defects, including a new "125" structure. It is likely that these fine-scale (10-30 Å thick) stacking defects are responsible for the significantly improved flux pinning in the phase-decomposed sample. It is proposed that the decomposition process begins with the reaction "248" 0><fv/0 "123"+"125", which could possibly occur by a spontaneous, short-range diffusion reaction. Further decomposition involves gradual removal of the extra CuO chains by long-range diffusion to produce a mixture of "123"+CuO.