Gaps between the platelets in melt-processed $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ ($R$=rare earth) superconductors

The origin of the “cracks” between the platelets in melt-processed $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ superconductors is investigated experimentally. The results convincingly demonstrate that these cracks actually develop during solidification. The relevance of this to the microstructural evolution during melt processing and to the critical-current densities is discussed.