【作者】 余见军；

【导师】 季惠明；

【作者基本信息】 天津大学 ， 材料学， 2008， 硕士

【摘要】 随着社会生产力的发展及广大人们生活水平的提高,气敏传感器得到了越来越广泛的应用,半导体电阻式气敏传感器是目前应用最广泛的传感器之一,成为研究的热点。本研究分别采用无机盐溶胶-凝胶法制备了MFeO₃（M=Sm、La）薄膜,采用传统工艺制备旁热式烧结型元件。对制备过程和丙酮气敏性能进行了讨论,揭示了组成-工艺-结构-丙酮气敏性能的内在联系,并对两类结构的气敏性能做了比较。以Sm（NO₃）₃·6H2O（La（NO₃）₃·6H2O）、Fe（NO₃）₃·9H2O等无机盐为原料,以柠檬酸为络合剂,配制成浓度为0.3mol/L的前驱体溶胶,在Al2O3基片上经过浸渍-提拉、干燥、预处理和烧结等过程制备了高质量纳米晶钙钛矿相MFeO₃薄膜。用FT-IR吸收光谱分析了前驱体的结构,以TG-DSC分析讨论了前驱体在烧结过程中的变化,用XRD分析了晶相,并用SEM表征了薄膜的表面形貌。分析了掺杂MFeO₃薄膜的阻温特性,呈现半导体氧化物的特征,根据曲线计算出材料的导电激活能,与理论相符合。MFeO₃薄膜对低浓度丙酮气体有良好的敏感性能:SmFeO₃薄膜在测试温度为450℃时,对30ppm丙酮气体灵敏度达到20,响应时间和恢复时间分别为15s和16s;LaFeO₃薄膜的丙酮灵敏度比SmFeO₃薄膜偏高,灵敏度达到22.5,响应时间和恢复时间分别为30s和20s。从缺陷和载流子的性质入手讨论了MFeO₃薄膜的导电机制和气敏机理。深入研究了测试温度、气体浓度、掺杂和膜厚对材料性能的影响。针对烧结型传感器,系统研究了工作电压、玻璃料添加剂,贵金属Pt以及掺杂对元件电阻和气敏性能的影响,获得了气敏元件最佳性能条件为:测试电压为4.5V,掺入1mol%Pt的SmFeO₃元件对10ppm丙酮气体灵敏度达到3.2。比较MFeO₃薄膜和烧结型元件气敏性能发现,薄膜材料由于高的表面活性和比表面积,对丙酮的灵敏度更大。考察了两类材料的选择性、稳定性,并对MFeO₃材料的气敏机理进行了探讨。指出未来气敏器件的发展方向为薄膜型元件。材料方面选择在低温下具有变化范围小的低电阻的材料,通过微量掺杂等手段提高气敏元件的选择性。更多还原

【Abstract】 With the improvement of social productivity and the life level of most people, gas sensors are used more and more widely. Semiconductor-typed gas sensor is one kind of most widely used gas sensors, which becomes a research hotspot at present. In this study, MFeO₃（M=Sm, La） thin films was prepared by inorganic salt sol-gel method; The indirectly heated and sintered type elements were prepared with traditional process. The synthetical processes and gas sensitive properties to acetone have been discussed. Relation of the composition, synthetical process, structure and sensitive property to acetone gas of LaFeO₃ thin films was investigated in this paper. The gas sensing properties of these two kinds of structures were compared.With citric acid used as complex agent , the precursor solution was prepared by dissolving Sm（NO₃）₃?6H2O（La（NO₃）₃?6H2O）, Fe（NO₃）₃?9H2O and other inorganic salts into water, of which the concentration was 0.3mol/L. MFeO₃ thin films with perovskite structure nano-crystalline grains were fabricated after the dip-coating, drying, pre-heating and sintering. FT-IR, TG-DSC, XRD and SEM were used to analyze the precursor and the thin films. Resistance vs. temperature properties of MFeO₃ thin films were analyzed, which showed the characteristics of semiconductor. According to the curves the conducting activation energy was figure out, which was coincided with the theory.The MFeO₃ thin films exposed to low concentration acetone gas showed good sensing properties. The sensitivity of SmFeO₃ to 30ppm acetone gas was 20, the response time was 15s, and the recovery time was 16s at the testing temperature of 450°C. The sensitivity of LaFeO₃ thin film was higher. The sensitivity was 22.5, the response time and the recovery time were 30s and 20s respectively. Its conductive and sensitive mechanism was proposed, with the types and concentration of defects and conductive carrier discussed. The effects of testing temperature, gas concentration, doping and film thickness to the properties of MFeO₃ thin films were deeply studied. The effects of testing voltage, glass frit, noble metal Pt and doping to the properties of the indirectly heated and sintered elements were systematic studied. It was found that the SmFeO₃ element has optimal gas sensing properties to 10ppm acetone, which doped 1mol% Pt at testing voltage 4.5V.Comparing to the properties of the thin film and sintered elements, it was seen that the sensitivity to acetone of thin film was higher because of high surface activity and specific surface area. The selectivity, the stability and the gas sensing mechanisms of MFeO₃ was discussed. It is pointed that the developing direction of gas sensor is thin film kinds elements. Materials of low resistance at low temperature are selected, of which the selectivity is improved by little doping methods.更多还原