We present the results of transport and microstructural studies on large single crystal and nearly bulk density polycrystalline samples of (RE)Ba2Cu3O7 superconductors. These samples were characterized by x-ray and electron diffraction, optical and scanning electron transmission microscopy, electrical resistance, magnetic susceptibility, and magnetic field and orientation dependent magnetization. Among some of the measurements we will report on are: unique features of the microstrure, superconducting fluctuations above the transition temperature, time dependent susceptibility, and critical currents.

Single crystals of YBa2Cu3O7 (1:2:3) were grown by melting mixtures of fine powders of 1:2:3, CuO and BaCuO2 and slow cooling through the peritectic regime under oxygen. There was a fairly broad composition range in the ternary phase field in which primary crystals formation is 1:2:3. Crystals were plate shaped, millimeter and submillimeter in size, with the c-axis of the unit cell perpendicular to the flat side of the plate. The onset of the superconducting transition was in excess of 90 K. Electron microscopy showed that the as-grown superconducting crystals were heavily twinned. These results suggest that larger crystals can be grown by Czochralski or Bridgman techniques using similar compositions.