Top-seeding melt texture growth of single-domain superconducting pellets

Abstract

The top-seeding melt texture growth (TSMTG) process is investigated in a small-vertical-thermal-gradient furnace in order to better understand the conditions for growing large single-grain pellets. An crystal was used as seed in a Y123 - Y211 composite with additions. It was shown that the role of the seed is to initiate the sympathetic nucleation growth mechanism. Indeed, the additional driving force induced by the seed is clearly demonstrated by a decrease in the undercooling of the system. The seeding crystal introduces a heterogeneous nucleation centre, leading to a very well controlled nucleation rate. Furthermore, we discuss the relation between intrinsic anisotropic growth rate and the processing rate, showing the importance of the thermal conditions of the texturing process to stabilize a sympathetic growth. By careful control of the texturing parameters, we succeeded in producing single-grain pellets as confirmed by a pole figure experiment and neutron diffraction measurements. The levitation force for pellets of 2 cm in diameter reaches 16 N when an NdFeB magnet of the same diameter is used.

Chemical characterization of melt-textured YBCO produced by hybrid powder metallurgy

“…The final assemblage thus has a modal composition exactly equivalent to that of the mixed powders. The top-seeding of the YBCO ensures that the degree of undercooling required for actual crystallization of the Y123 is small [11].…”

Improvement on the melt-texturing performance of a (Y,Ta)0.5BaO3–YBa2Cu3Oy composite with superconductor applications

“…A number of efforts have intensively been taken in the critical current density of a melt-texture YBa 2 Cu 3 O 7 À d (Y123) superconductor since the discovery of the high-T c superconductor (HTS) [1][2][3]. Various investigations have focused on the melt process of the Y123 oxides [3].…”

“…Various investigations have focused on the melt process of the Y123 oxides [3]. It has been previously reported [4][5][6][7][8][9] that both alignment of grains and decreased grain boundaries are responsible for some improvements on the J c (critical current density).…”

“…Alternatively, a seed of the single crystal process should provide a massive material in a reduced time. This means that the drive-force should be commonly called as a top seed melt growth [26][27][28][29][30][31].…”

The contribution of 211 particles to the mechanical reinforcement mechanism of 123 superconducting single domains

“…technique [5][6][7]. Single-crystals of SmBa 2 Cu 3 O 7-δ (Sm-123) or NdBa 2 Cu 3 O 7-δ (Nd-123) serve as effective seed for Y-123 due to the similar lattice parameters of these 123-compounds.…”