Development of functional devices using hot spot in GdBa2Cu3O7−δ-based composite ceramics

A hot spot, which is a local area glowing orange, appears in LnBa2Cu3O7−δ (Ln: rare earth element) 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 such as a constant-current generator, an oxygen sensor. The durability of the rod during a sustained presence of the hot spot is improved upon adding BaAl2O4 into the GdBa2Cu3O7−δ. In this paper, GdBa2Cu3O7−δ-based composite ceramic rod with various BaAl2O4 contents were prepared by solid-state reaction, and current–voltage characteristics and temperature dependences of resistivity were measured. The minimum electric power required for the hot spot to appear increased with increasing BaAl2O4 content. From the temperature dependence of the resistivity, temperature just before the hot spot appearance could be successfully estimated. The minimum electric power required for the hot spot to appear can be expected from the temperature dependence of the resistivity of the ceramics, which is useful to design the functional devices exploiting the hot spot.