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

通过控制晶界微观结构进行环境监测的压敏电阻式气体传感器的设计

• 批准号: 12450270
• 负责人: SHIMIZU Yasuhiro
• 金额: $ 9.6万
• 依托单位: Nagasaki University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450270/
• 关键词: SnO_2-Cr_2O_3; NO_x sensor; Zeta potential; Pd; TiO_2; Anodic oxidation; H_2 sensor; WO_3; SO_2 sensor; SnO_2; 表面処理; 界面接合状態; SO_2; バリスタ型ガスセンサ; 酸化スズ; 酸化クロム; p-n接合; NO_x; ダブルショットキー障壁; ブレークダウン電圧

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

本课题主要研究了以下四个方面的内容，取得的主要成果如下：1）SnO_2-5Cr_2O_3系压敏型传感器的晶界结构与NO_x、传感性能的关系研究了SnO_2-5Cr_2O_3系压敏型传感器的晶界结构和在空气和N_2中的击穿电压。为了阐明SnO_2-5Cr_2O_3对NO的敏感性高于对NO_2的敏感性的机理。当Cr_2Or_3的添加量达到5wt%时，SnO_2-SnO_2晶界的数量增加，NO和NO_2气敏性均提高。研究了SnO_2-Cr_2O_3半导体气敏元件的NO_x气敏特性，研究了SnO_2-Cr_2O_3半导体气敏元件的电位与NO_x气敏特性之间的关系，并与SnO_2-Cr_2O_3半导体气敏元件进行了比较 ...更多信息 d.用转移印刷法制备的SnO_2-Cr_2O_3厚膜半导体气敏元件。SnO_2-Cr_2O_3型半导体气敏元件对NO的灵敏度低于NO_2型气敏元件，压敏型气敏元件对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试样的过电位从-12 mV突然升高到+12 mV。在SnO_2-Cr_2O_3基样品中，SnO_2表面是NO_2的活性中心，而微p-n结是NO的活性中心。3）高灵敏度SO_2气敏元件的研制及其气敏机理在所测试的氧化物中，WO_2在400℃时具有最高的灵敏度，当Ag含量为1.0wt%时，其灵敏度进一步提高。通过对Ag负载的促进作用的详细研究，提出了在SO_2暴露时传感器的电阻变化是由于SO_2与负载Ag上的两个O_2 ~（2-）ad反应生成SO_4 ~（2-）引起的。4）阳极氧化TiO_2膜与Pd电极接触作为二极管型H_2传感器<2->。并测试了它们的H_2敏感性能，作为通过控制传感器与电极材料界面微结构实现高敏感性能的途径。与Pd电极接触的TiO_2膜在空气和N_2中均表现出二极管型的电流-电压特性和可逆的H_2响应。在反向偏压条件下，在N_2中获得了比空气中更高的H_2响应。H_2在N_2中的可逆响应被认为是由于H_2在Pd表面解离，导致Pd/TiO_2界面势垒高度的变化，进而使H原子溶解到电极用Pd中。这种独特的传感器将用于特殊的无氧环境下的H_2检测。少