It is critically important to increase mechanical properties of RE-Ba-Cu-O bulk superconductors for practical applications. In this paper, we first studied the formation mechanism of cracking in Y-Ba-Cu-O and Sm-Ba-Cu-O massive blocks. The cracking is formed with the thermal stress during the thermal cycles, in particular, for large grain samples. The tetragonal to orthorhombic phase transformation also causes cracking mainly along the (001) cleavage planes. In addition, the cracks have the chance to propagate when strong magnetic fields are applied. Sm-Ba-Cu-O seems to be intrinsically more sensitive to cracking due to the larger lattice parameters than Y-Ba-Cu-O. However, microstructure is more important in determining the mechanical properties such as the homogeneity of RE211 inclusions or pores. Ag addition was found to be effective in improving the mechanical properties through the densification and/or the reduction in defect density.
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