Design of Varistor-Type Gas Sensors for Environmental Monitoring by Controlling Microstructure of Grain-boundaries

本项目主要研究了以下四个课题，所得结果总结如下：研究了SnO_2-5Cr_2O_3型压敏电阻型传感器在空气和氮气中的显微结构与击穿电压的关系，阐明了SnO_2-5Cr_2O_3型传感器对NO的灵敏度高于No_2的机理。当Cr_2Or_3添加量达到5 wt%时，SnO_2-SnO_2晶界数目增加，NO_2气敏性增加。由于微p-n结的形成，在高温下稳定的NO化学吸附被认为是高NO敏感性的原因。2) NO_x， SnO_2-Cr_2O_3薄膜半导体气体传感器的气敏性能。本文研究了滑动转移印刷法制备SnO_2-Cr_2O_3厚膜半导体气体传感器的ζ电位与NO_x传感性能的关系。SnO_2-Cr_2O_3作为半导体气体传感器对NO的灵敏度高于NO_2，而压敏电阻型传感器对NO灵敏度的提高受到限制。在0 ~ 1.0wt% Cr_2O_3范围内，SnO_2-Cr_2O_3试样的温度从- 12 mV急剧升高到+12 mV。对于SnO_2- cr_2o_3基样品，可以认为SnO_2表面是NO_2检测的活性位点，而微p-n结是NO检测的活性位点。3)高灵敏度SO_2气体传感器的研制及其传感机理研究了几种金属氧化物作为厚膜半导体SO_2气体传感器的实验研究。在所测试的氧化物中，WO_2在400℃时表现出最高的灵敏度，并在1.0 wt% Ag的负载下进一步增强。短句来源通过对Ag负载促进效应的详细研究，提出了SO_2作用下传感器的电阻变化是由于SO_2与两个O_2^- ad在负载的Ag上反应生成SO_4^<2->引起的。4)制备了与Pd电极接触的二氧化钛阳极氧化膜作为二极管型H_2传感器，并对其H_2传感性能进行了测试。通过控制传感器与电极材料界面的微观结构，实现高传感性能。与Pd电极接触的TiO_2膜在空气和氮气中均表现出二极管型的电流-电压特性和可逆的H_2响应。在反向偏置条件下，氮气中的H_2响应比空气中的H_2响应高。H_2在N_2中的可逆响应被认为是由Pd表面H_2的解离和随后H原子溶解到用于电极的Pd体中引起的Pd/TiO_2界面势垒高度的变化引起的。这种独特的传感器将用于无氧特殊环境下的H_2检测。少

The following four subjects have been mainly studied in this project, and the results obtained are summarized below.I) Relationship between microstructure of grain-boundaries and NO_x, sensing properties of SnO_2-5Cr_2O_3 based varistor-type sensorsMicrostructure and breakdown voltage in both air and N_2 have been investigated for SnO_2-Cr_2O_3 varistor-type sensors, in order to clarify the mechanism for higher NO sensitivity than No_2 observed for SnO_2-5Cr_2O_3. Increase in both NO and NO_2 gas sensitivity arose from the increase in the number of SnO_2-SnO_2 grain boundaries up to an additive amount of 5 wt% Cr_2Or_3. Stabilized NO chemisorption up to elevated temperatures owning to the formation of micro p-n junctions is considered to be responsible for the higher NO sensitivity.2) NO_x, gas sensing properties of Nick film SnO_2-Cr_2O_3 as semiconductor gas sensors fabricated by slide-off transfer printing.Relationship between ζ potential and NO_x, sensing properties has been studie … More d for thick film SnO_2-Cr_2O_3 fabricated by slide-off transfer printing as semiconductor gas sensors. SnO_2-Cr_2O_3 as semiconductor gas sensors showed tower NO sensitivity than NO_2, and achievement of higher NO sensitivity was limited for the varistor-type sensor. Ζpotential of SnO_2-Cr_2O_3 specimens increased abruptly from - 12 to +12 mV in the range of 0〜1.0wt% Cr_2O_3. In the case of SnO_2-Cr_2O_3 based specimens, it is considered that the SnO_2 surface acts as active sites for NO_2 detection, while micro p-n junctions for NO detection.3) Development of an SO_2 gas sensor with high sensitivity and its sensing mechanismSeveral metal oxides have been tested as thick film semiconductor SO_2 gas sensors. Among the oxides tested WO_2 was found to exhibit the highest sensitivity at 400℃, and further enhancement could be achieved by loading of 1.0 wt% Ag. From the detailed studies on the promotion effect induced by the Ag loading, resistance change of the sensor upon exposure to SO_2, is suggested to arise from the formation of SO_4^<2-> by the reaction between SO_2 and two O_2^- ad on the Loaded Ag.4) Anodically oxidized TiO_2 film contacted with Pd electrode as diode-type H_2 sensorAnodically oxidized TiO_2 films have been prepared, and they H_2 sensing properties have been tested, as an approach for realizing high sensing performance by controlling microstructure at the interface between sensor and electrode materials. The TiO_2 film contacted with Pd electrode showed diode-type current-voltage characteristics and reversible H_2 response in both air and N_2. Higher H_2 response was achieved in N_2 than in air under reverse bias conditions. The reversible H_2 response in N_2 is considered to arise from the change in barrier height at Pd/TiO_2 interface induced by dissociation of H_2 at the Pd surface and subsequent dissolution of H atoms into Pd bulk used for the electrode. Such a unique sensor will be used for H_2 detection under special environments containing no oxygen. Less