Study on single domain growth of Ag-doped Sm-Ba-Cu-O bulk using cold seeding technique

Attempts to prepare single grain SmBCO/Ag using NdBa2Cu3O7−δ (Nd123) cold seeding technique have been performed. As silver decreases the melting temperature of SmBa2Cu3O7−δ (Sm123) to approximately 1028 °C, it becomes possible to texture SmBCO/Ag samples with the Nd123 cold seeding technique, and very well textured mono-domain crystals with 15 mm on a side have been successfully obtained. However, the growth rate of SmBCO/Ag system is severely reduced compared with Ag free sample. A series of samples quenched at various lower limit temperatures of slow-cooling process were fabricated to investigate the single domain growth of SmBCO/Ag system. It is found that mono-domain growth exhibits a suppressed tendency within the slow-cooling temperature window considered, and then is hindered significantly by the spontaneous nucleation. The transversal slides of these samples show that large amount of entrapped gas did not escape from the samples during the dwell time at the maximum superheating temperature. During the slow-cooling process, the entrapped gas continued to move towards the edges of the samples, coalesced with each other and very large pores several millimeters in size were formed, which finally were released from the sample. The SEM analysis reveals that the coarsening of Sm2BaCuO5 (Sm211) precipitates has occurred during the growth of mono-domain. Large Sm211 cause decreased ability to supply samarium for the growth of Sm123 crystal, resulting in a gradual decrease in the growth rate.