Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O7-x superconductor and their correlation with room-temperature ultrasonic measurements

The purpose of this study was to (1) examine the spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O7-x specimens over the pore fraction range 0.10--0.25 and (2) determine the viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability. Spatial variations in a.c. susceptibility were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in a.c. shielding and loss behavior. Optical quantitative image analysis on sample cross sections revealed pore fraction to be the varying microstructural