title: Application of convergent beam electron diffraction in the structural study of high-temperature superconducting oxides.
abstract: Convergent beam electron diffraction (CBED) is a powerful technique for symmetry study of crystal. It has widespread application in physics and material sciences, as demonstrated in a recent superconducting oxide study. Using this technique, we have studied Ba-La-Cu-O superconductors with a transition temperature of about 40 degrees K and Ba-Y-Cu-O superconductors with a critical temperature (Tc) of about 90 degrees K. We have found that in Ba-La-Cu-O superconductors the superconducting phase La2-xBaxCuO4-y has a distorted K2NiF4-type structure and the space group Fmmm. The two other phases in Ba-La-Cu-O superconductors have also been studied. In our Ba-Y-Cu-O superconductors, the Ba2YCu3O7-x compound, which is responsible for 90 degrees K superconductivity, has two different space groups: An orthorhombic space group Pmmm and a tetragonal space group P4mm or P4/mmm.
mesh_terms: D003461:Crystallography; D004553:Electric Conductivity; D008854:Microscopy, Electron / Q000379:methods; D015394:Molecular Structure; D010087:Oxides / Q000032:analysis*; D013696:Temperature; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D010087:Oxides