Fabrication and characterization of large Nd-Ba-Cu-O grains prepared under low oxygen pressure

A large, single-grain Nd-Ba-Cu-O (NdBCO) composite consisting of superconducting NdBa2Cu3O7-delta containing nonsuperconducting Nd4Ba2Cu2O10 phase inclusions was fabricated up to 2 cm in diameter using a top-seeded melt-textured growth technique. A MgO single-crystal seed was used to provide a heterogeneous nucleation site at the center of a presintered pellet heated above its peritectic temperature and cooled continuously in a conventional tube furnace in reduced oxygen partial pressure. This process produces individual grains with the c axis oriented at approximate to 10 degrees to the seed surface which, from vibrating-sample magnetization measurements, exhibit a pronounced peak effect in their magnetic moment over a wide temperature range (50-90 K) when the supercurrent flows in the a-b planes. A very high irreversibility field (>9 T at 77 K) is also observed in these grains for field applied both perpendicular and parallel to the crystallographic c axis which is significantly greater than that observed in good-quality melt-processed Y-Ba-Cu-O. These results underline the potential of NdBCO for high-field engineering applications.