The influence of Nd–Ba–Cu–Mg–O generic seed crystal composition on Tc of seeded, bulk (RE)–Ba–Cu–O grains

A Mg-doped Nd–Ba–Cu–O generic seed crystal has been developed for the fabrication of any type of rare earth (RE) based (RE)–Ba–Cu–O single grain superconductor by the top seed melt growth (TSMG) technique. Melt processed crystals of Nd–Ba–Cu–O enriched with various amounts of MgO exhibit increased melting points compared to other (RE)–Ba–Cu–O systems, whilst retaining a similar crystal structure. The Mg-doped Nd–Ba–Cu–O phase is stable with Ba–Cu–O liquid at elevated temperature and, as a result, can be used to seed the growth of any (RE)–Ba–Cu–O single grain. Key seed properties have been investigated as a function of MgO content, including Tc, the distribution of MgO inclusions within the YBa2Cu3O7−δ (Y-123) matrix, melting point and composition. MgO doping results usually in a decrease in Tc of the parent (RE)BCO compound. It is particularly important, therefore, to investigate fully any variation of Tc associated with the diffusion of Mg into a grain grown from a Mg-containing seed. We report the superconducting and microstructural properties of YBCO, SmBCO and GdBCO single grains fabricated using various Nd–Ba–Cu–Mg–O generic seed crystals with a wide range of MgO content. Finally, we report the optimum composition of Nd–Ba–Cu–O generic seed crystal from a study of the variation of Nd–Ba–Cu–O melting temperature with concentration of Mg in the precursor seed composition.