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

当在室温下对REBa2Cu3O；7-δ&gt；(Re：稀土元素)陶瓷棒施加一定的电压时，棒中出现一个发光热点。本项目旨在研究热点引起的各种功能的出现机理和可行的应用。研究结果表明：(1)热斑向负极迁移的机理与热斑中的氧离子传导有关；(2)热斑热处理提高了棒材的临界电流密度；(3)热斑氧传感器具有优良的传感性能，适用于多种用途。(4)热斑出现在(Ln&lt；1-x&gt；Srx)(Co&lt；1-y&gt；Fey)O&lt；3-δ&gt；(LN：稀土元素)陶瓷棒。通过对陶瓷成分的控制，可以设计出不同用途的氧传感器的传感性能。(5)当棒的长度小于一定值时，由热斑引起的细小恒流特性是不存在的。当氧分压低于一定值时，当出现热点时，阻尼型振荡电流流过棒体。通过控制周围气体的导热系数、棒的横截面积、外加电压和周围大气中的氧分压，可以设计出振荡频率和衰减时间常数。利用这一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.