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：1)SnO_2-5Cr_2O_3系压敏元件晶界微结构与NO_x的关系及其传感性能研究了SnO_2-Cr_2O_3系压敏元件在空气和氮气中的微结构和击穿电压。为了阐明SnO_2-5Cr_2O_3的NO敏感性高于NO_2的机理，我们观察到SnO_2-5Cr_2O_3的NO和NO_2气体敏感性都有所提高，这是由于SnO_2-SnO_2晶界数目增加到5wt%Cr2Or_3的添加量。由于形成微小的p-n结而导致的高温下稳定的NO化学吸附被认为是导致较高的NO敏感性的原因。滑脱转印法制备SnO_2-Cr_2O_3半导体气敏元件研究了ζ电势与NO_x的关系以及气敏特性与…的关系用滑脱转移印刷法制备了SnO_2-Cr_2O_3厚膜半导体气敏元件。SnO_2-Cr_2O_3作为半导体气敏元件，其灵敏度不高于NO_2，而压敏式气敏元件对NO的高灵敏度的实现是有限的。在0~1.0wt%Cr_2O_3范围内，SnO_2-Cr_2O_3样品的Ζ电位从-12 mV突然增加到+12 mV。对于SnO_2-Cr_2O_3基样品，认为SnO_2表面是NO_2检测的活性中心，而微p-n结是NO_2检测的活性中心。3)高灵敏度SO_2气敏元件的研制及其传感机理。在所测试的氧化物中，WO_2在400℃时表现出最高的灵敏度，负载1.0wt%的银可以进一步增强。通过对Ag负载的促进效应的详细研究，提出了传感器在SO_2中的电阻变化是由于SO_2与负载型Ag上的两个O_2^-ad反应生成了SO_4~(2-)和~(2-)Gt~(2-)。4)阳极氧化的TiO_2膜作为二极管型H_2传感器，制备了阳极氧化的TiO_2膜，并对其氢敏性能进行了测试，作为一种通过控制传感器与电极材料界面微结构实现高传感性能的途径。与Pd电极接触的二氧化钛薄膜在空气和氮气中都表现出二极管型的伏安特性和可逆的氢气响应。在反向偏压条件下，氮气中的氢气响应比空气中的高。在N_2中的可逆H_2响应被认为是由于Pd表面H_2的解离和H原子随后溶解到电极所用的Pd体内而引起的Pd/TiO_2界面势垒高度的变化。这种独特的传感器将用于在不含氧的特殊环境下进行氢气检测。较少