Novel sponge-like structure created in GdBa2Cu3O7−δ ceramics by hot spot

A hot spot, which is a local area glowing orange, appears in a GdBa2Cu3O7−δ ceramic rod when a voltage exceeding a certain value is applied to the rod at room temperature. The rod with the hot spot shows various functional characteristics that give rise to applications in devices. We found that the hot spot created a sponge-like structure in the rod. The elemental map revealed that the sponge-like structure was composed of Gd2BaCuO5 grains. The hot spot is considered to decompose GdBa2Cu3O7−δ into Gd2BaCuO5 and liquid phase, and the liquid phase moves toward the periphery of the rod, leaving sponge-like structure composed of Gd2BaCuO5 grains. The novel sponge-like structure created in the GdBa2Cu3O7−δ rod by the hot spot may bring about new applications for magnetic separations of fluids.