Multi-seeded growth of melt processed Gd–Ba–Cu–O bulk superconductors using different arrangements of thin film seeds

Gd–Ba–Cu–O (GdBCO) bulk superconductors of diameter of 42 mm have been fabricated via a multi-seeded melt growth (MSMG) method in air using well-oriented Nd–Ba–Cu–O thin film seeds. The effect of seed orientation on the growth process and the formation of grain boundaries were investigated systematically by using two thin film seeds arranged with crystallographic orientations of (100)/(100) and (110)/(110), respectively. The multi-seeded process was then firstly extended to four thin film seeds arranged asymmetrically [(110)/(110)], which involved placing the seeds in pairs, with two adjacent seeds positioned relatively close to each other and the other two at a greater separation. This modified technique is beneficial to obtain a large size GdBCO bulk in a shorter time as well as clean grain boundaries by rejecting the excess melt liquid thoroughly along the growth front. More interestingly, a domain of non-equilibrium shape is formed during the MSMG process, which leads potentially to the growth of much larger samples. The growth mode of the enhancement in growth rate is interpreted by the presence of a high index crystallographic (110) face to the initial growth front.

► Large-sized GdBCO bulk superconductors were grown by multi-seeding process. ► The effect of seed arrangement on the formation of grain boundaries was studied. ► The use of an asymmetrical (110)/(110) arrangement of seeds was developed for potentially enhancing the property of as-grown samples. ► An unexpected domain of non-equilibrium shape is formed during the melting process. ► An explanation on the formation of the non-equilibrium shape is proposed.