Preparation and magnetic properties of YBa 2Cu 3O 7−x single crystals containing Y 2BaCuO 5 and barium titanate inclusions

Abstract

Large single crystals of YBCO are grown by melt textured growth in ceramic pellets. Starting powders of Y 1.5–1.8Ba 2Cu 3O x with the addition of 5 wt% BaTiO 3 are used for the pellets. The peritectically grown single crystals are mechanically extracted from the melt textured blocks. The microstructure is characterized by optical microscopy, scanning electron microscopy and electron microprobe analysis. SEM micrographs show a high density of crystal defects like Y 2BaCuO 5 and YBaTiO inclusions. Between the a– b planes extended planar defects are found. This growth morphology is typical of melt textured YBCO. The anisotropic magnetic properties are measured with a vibrating sample magnetometer. Magnetization loops for the external field orientation parallel to the crystal c-axis indicate critical current densities larger than 1 × 10 4 A cm −2 up to 2 T at 77 K. Typically the magnetization loops show an extended high field peak. It was found that the high field peaks are correlated with the oxygenation state of the sample. The temperature shift of the peak field is different from that of the irreversibility field. If applying the Bean or Gyorgy model to estimate the critical current densities it is important to consider sample shape effects.