Hot spot phenomenon originated from the grain boundary of high-Tc superconducting ceramics and the application

在室温下，对ReBa_2Cu_3O_（7-δ）（Re：稀土元素）陶瓷棒施加一定的电压，在棒中出现发光热点。本计画旨在探讨热斑所引起的各种功能的产生机制及可行的应用。从研究中获得了以下结果。(1)热点向负极迁移的机理与热点中的氧离子导电有关。(2)采用热斑热处理提高了棒的临界电流密度。(3)使用该热点的氧传感器具有优异的感测特性，并且对于各种用途都是可行的。(4)在（Ln_<1-x>Sr_x）（Co_<1-y>Fe_y）O_（3-δ）（Ln：稀土元素）陶瓷棒中出现了热节。通过控制陶瓷的组成，氧传感器的感测特性可以被设计用于各种用途。(5)当棒的长度小于一定值时，热斑引起的良好的恒流特性将不复存在。杆的导热性的降低对于装置的小型化是有效的。(6)当氧分压低于一定值时，出现热点，阻尼振荡电流流过棒。通过控制周围气体的热传导、棒的横截面积、施加的电压和环境气氛中的氧分压，可以设计振荡频率和衰减时间常数。利用这种现象可以实现超低频振荡器。

When a certain voltage is applied to ReBa_2Cu_3O_<7-δ> (Re : rare-earth element) ceramic rod at room temperature, a glowing hot spot appears in the rod. This project was aimed at investigating the appearance mechanism of various functions caused by the hot spot and the feasible applications. The following results were obtained from the research.(1) The mechanism of the hot spot migration toward the negative electrode is related to the oxide ion conduction in the hot spot.(2) The heat treatment using the hot spot improves the critical current density of the rod.(3) The oxygen sensor using the hot spot has an excellent sensing property and it is feasible for various uses.(4) A hot spot appears in (Ln_<1-x>Sr_x) (Co_<1-y>Fe_y) O_<3-δ> (Ln : rare-earth element) ceramic rod. By controlling the composition of the ceramics, the sensing property of the oxygen sensor can be designed for the various uses.(5) The fine constant current characteristic caused by the hot spot is unavailable when the rod is shorter than a certain value. A decrease in the thermal conductivity of the rod is effective for the miniaturization of the device.(6) When a hot spot appears under lower oxygen partial pressure than a certain value, a damped oscillatory current runs through the rod. It is possible to design the oscillation frequency and the time constant of decay by controlling the thermal conduction of surrounding gas, the cross-section area of the rod, the applied voltage and the oxygen partial pressure in ambient atmosphere. An ultra low frequency oscillator can be realized by using this phenomenon.