We have studied the microstructures and superconducting properties of melt-processed (RE,RE′)-Ba-Cu-O composite bulks (RE and RE′ are two different rare earth elements selected from a group of Nd, Sm, Eu, Gd and Y). It was found that the peritectic decomposition temperatures (Tm) of the (RE,RE′)-Ba-Cu-O composites increased linearly with increasing the average ionic radius between two different rare earth elements. Large grain growth was observed in almost all the (RE,RE′)-Ba-Cu-O bulks except those containing Y, when they were melt-processed in a reduced oxygen atmosphere. Compositional analyses revealed that the ratio of RE to RE′ in the (RE,RE′)Ba2Cu3O7-d matrix phase was almost the same as that of the nominal composition, showing that the mixture of the two different rare earth elements was very uniform. All the samples showed onset superconducting transition temperatures (Tc) exceeding 93 K with a sharp transition, and exhibited a secondary peak effect in the M-H loops.
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