| With the development of society,the gas and humidity sensors play an increasingly important role in industry,agriculture,smart home,environmental monitoring and other fields,and it is urgent to develop high performance gas and humidity sensors.In this paper,ABO3 perovskite composite metal oxide LaFeO3 and La0.7Sr0.3MnO3 are used to fabricate gas and humidity sensors.According to the research process of material preparation,material characterization,device fabrication,performance testing and mechanism analysis,the gas and humidity properties of LaFeO3 and La0.7Sr0.3MnO3 nanomaterials were systematically studied,and the main results are as follows:1.LaFeO3 nanoparticles were synthesized by sol-gel method and characterized by X-ray diffraction(XRD),field-emission scanning electron microscopy(FE-SEM)and X-ray photoelectron spectroscopy(XPS).The mixed-potential type NO2 gas sensors Pt/YSZ/LaFeO3 were fabricated using LaFeO3 nanoparticles as sensing electrode(SE),Y2O3-stabilized ZrO2(YSZ)film as electrolyte and platinum(Pt)as reference electrode(RE).The gas sensing properties of the gas sensor were investigated at different operating temperatures and NO2 concentrations.The results showed that the maximum response value was about 164 mV to 100 ppm NO2 at 300 ?,and the response and recovery times were about 73 s and 94 s.The gas sensors exhibited a nearly linear response at NO2 concentrations range of 50-400 ppm,and the sensitivity reached up to 353 mV/decade.2.LaFeO3 nanotubes were fabricated via a single needle electrospinning method combined the rapid annealing technology.The morphologies of LaFeO3 nanotubes were characterized by FE-SEM and TEM.The characterization results showed that the LaFeO3 nanotubes were of clear hollow tubular structure,and their outer and inner diameters were about 50 nm and 30 nm,respectively.The gas sensor based on LaFeO3 nanotubes was fabricated and its gas sensing properties including ethanol,formaldehyde,acetone and ammonia were tested.The results showed that the LaFeO3 nanotubes gas sensor was of the largest response to ethanol,and the response value to 100 ppm ethanol was about 9.4 at 160 ?.The response/recovery times were about 2 s and 4 s,respectively,and the gas sensor exhibited a good linearity(R2=0.97)in 5-100 ppm ethanol.In addition,the humidity sensor based on LaFeO3 nanotubes was fabricated and its humidity sensing properties were investigated.The optimum working frequency of the LaFeO3 nanotubes humidity sensor was 100 Hz and the impedance variation was about three orders of magnitude in 11%-95%RH.3.La0.7Sr0.3MnO3 nanocrystals were prepared by polyvinylpyrrolidone(PVP)-assisted sol-gel method and characterized by XRD,FE-SEM,TEM,XPS,specific surface and pore size analysis and contact angle.The characterization results showed that the La0.7Sr0.3MnO3 nanocrystals were of good nanocrystalline structure,large specific surface area and super hydrophilic properties.The gas sensor based on La0.7Sr0.3MnO3 nanocrystals was fabricated and its gas sensing properties including ethanol,formaldehyde,acetone and ammonia were studied.The results showed that the La0.7Sr0.3MnO3 nanocrystals gas sensor was of relatively poor response to the above reducing gases.Secondly,the humidity sensor based on La0.7Sr0.3MnO3 nanocrystals was fabricated.The test results showed that the La0.7Sr0.3MnO3 nanocrystals humidity sensor was of excellent sensing properties:the impedance variation of the sensor was about four orders of magnitude(11%-95%RH)at 10 Hz,the response/recovery times were as low as 0.8 s and 4.9 s,and the humidity hysteresis was only about 4%RH.Compared with the gas sensing properties,La0.7Sr0.3MnO3 nanocrystals are of the better humidity sensing properties. |
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