Microstructural observations of RBa2Cu3O7 (R = Gd, Y, and Tm) superconductor thin crystals between 15 and 1000 K

Small crushed crystals of the new superconductor materials of the type RBa2Cu3O7 (R = Gd, Y, and Tm) were studied by conventional transmission electron microscopy between 15 and 1000 K. Between 15 and 300 K a He-liquid cold stage was used, while temperatures between 300 and 1000 K were obtained by focusing the electron beam. The thin-edge areas unambiguously show the formation of the classical orthorhombic structure. The orthorhombic-tetragonal transition, in the course of the cooling, was not observed. Electron diffraction results show the presence of various unknown structures and the BaCuO2 compound. The crystals present few defects: Only some twins and dislocations have been observed