GRAIN-BOUNDARY STUDIES OF HIGH-TEMPERATURE SUPERCONDUCTING MATERIALS USING ELECTRON BACKSCATTER KIKUCHI DIFFRACTION

Grain orientation and grain boundary misorientation distributions in h igh critical current density, high-temperature superconductors were de termined using electron backscatter Kikuchi diffraction. It is found t hat depending on the type of superconductor and the processing method used to fabricate it, there exist different scales of biaxial texture from no biaxial texture, local biaxial texture, to complete biaxial te xture. Experimentally obtained grain boundary misorientation distribut ions (GBMDs) were found to be skewed significantly to low angles in co mparison to what is expected on the basis of macroscopic texture alone , suggesting that minimization of energy may be a driving force during the processing of high critical current density materials. In additio n, a higher than expected fraction of coincident-site lattice boundari es is observed. Examination of maps of grain boundary misorientations in spatially correlated grains, i.e. the grain boundary mesotexture, s uggests the presence of percolative paths of high critical current den sity. A combination of orientation measurements, theoretical modeling of GBMDs and modeling of percolative current flow through an assemblag e of grain boundaries is performed to gain an insight into the importa nt microstructural features dictating the transport properties of high -temperature superconductors. It is found that maximization of low ene rgy, in particular, low-angle boundaries, is essential for higher crit ical currents. The combination of experimental and analytical techniqu es employed are applicable to other materials where physical propertie s are dominated by intergranular characteristics.