Development of Bi alloy insulator composites exhibiting metal-insulator-transition-like resistivity change

在本项目中，我们研究了“金属-绝缘体过渡类PTCR材料：双绝缘体复合材料”，以开发一种新型的热敏过电流限制器。该复合材料利用温度变化在由铋微粒组成的金属网络中的自固定过程。制作了两个样机，不仅是为了验证PTCR机理，也是为了制作电子元件。此外，还研究了微波加热对改善常用陶瓷材料PTCR性能的影响。所得结果如下：1)Bi型聚酰亚胺复合材料的室温电阻率ρ_&lt；Rt&gt；在加热和冷却过程中循环一次后增加。另一方面，在双玻璃复合材料中，即使在反复的热应力下，ρ_&lt；RT&gt；仍保持稳定在~1Ωcm。铋玻璃复合材料的高温电阻率ρ&lt；Ht&gt；大于10^6Ωcm。2)在微观结构观察的基础上，提出了铋玻璃复合材料的PTCR机理。ρ-T关系中的滞后特性表现为铋微粒的冻结过程。3)铋锡合金-玻璃复合材料的电阻率变化临界温度比铋玻璃复合材料低约100K，接近于PTCR BaTiO_3的临界温度。但ρ-T关系表现出半导体特性，ρ_&lt；HT&gt；/ρ_&lt；RT&gt；一种是铋填充的微管，另一种是在玻璃板上溅射的铋设计的微图形。5)虽然微波加热降低了BaTiO_3陶瓷的ρ_lt；RT&gt；，但其PTCR性能不如铋玻璃复合材料。

In this project, we have investigated "metal-insulator transition like PTCR material : Bi-insulator composite" to develop a new type of thermo-sensitive over-current limiter. The composite utilizes self-fixing process in metal-networks composed of Bi micro-particles depending on temperature change. Two prototypes have been made not only for verifying the PTCR mechanism but also for fabricating the electrical element. Besides, effect of microwave heating was studied to improve the PTCR property of the usual ceramics material. Obtained results are summarized as follows.1) The ρ_<RT>, resistivity at room temperature, of Bi-polyimide composite increases after one cycle of heating and cooling process. On the other hand, in Bi-glass composite the ρ_<RT> was kept stable at 〜 1 Ωcm even with repeated thermal stresses. The ρ_<HT>, resistivity at high temperature, of the Bi-glass composite was higher than 10^6 Ωcm.2) We proposed the PTCR mechanism for the Bi-glass composite in terms of "Bi-metal micro-networks" based on the microstructure observations. The hysterisis characteristic in ρ - T relation was expressed by freezing process of Bi micro-particles.3) The critical temperature of the resistivity change in Bi-Sn alloy-glass composite was 〜 100K lower than that of Bi-glass composite, which is close to that of a PTCR BaTiO_3. However, the ρ - T relation shows semiconductor characteristics and the ρ_<HT>/ρ_<RT> is lower than 1.4) We have made two prototypes of Bi-glass with PTCR property. One is micro-tube filled with Bi, and another is micro-pattern designed by sputtered Bi on a glass plate. In both elements Bi micro- particles with micron or lower in size should be packed in glass matrix for obtaining PTCR property.5) Although ρ_<RT> of BaTiO_3 ceramic was reduced by microwave heating, the PTCR property is inferior to that of Bi-glass composite.