We report on the effect of the atmosphere during the decomposition of the precursors of Sm-Ba-Cu-O bulk superconductors. It was found that the formation of voids was greatly suppressed by two methods, melting in an oxygen gas atmosphere or in vacuum. For both methods, the atmosphere during crystallization was switched to an Ar gas flowing one. The samples prepared by these methods exhibited high superconducting transition temperatures with sharp transition widths. However, the zero-field critical current density was lower than that of the reference sample, which was prepared by decomposing the precursor in an Ar gas flowing atmosphere.
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