Application of low-angle polishing for rapid assessment of the texture and morphology of thick film Y₁Ba₂Cu₃O₇ superconducting tapes

Metallographic polishing was used for the rapid assessment of the texture quality of 2 μm thick YBa₂Cu₃O₇ (YBCO) layers deposited on oxide buffered RABiTS^™ metal substrates. The YBCO films were grown using the barium fluoride ex situ process. The method is based on partial removal of the YBCO layer by mechanical polishing, resulting in the formation of a 200-300 μm wide wedge of YBCO material with an approximately linear thickness profile. Due to the linearity of the thickness profile of the wedge, the depth below the film surface, of any visible structural detail in the wedge area, can be determined by simply measuring the lateral distance from the detail of interest to the film surface/wedge intersection. In this study the wedge area was inspected by optical microscopy for changes in morphology, twin plane pattern, and YBCO grain size. It is demonstrated how X-ray diffraction, combined with low-angle polishing can help establish the origins of YBCO texture degradation in the sub-surface layers of thick YBCO films. It is concluded that homogeneous nucleation is responsible for the appearance of random texture in sub-surface YBCO layers.