Gas Sensitivity Of Perovskite-Type Oxide Nanomaterials Based On YbFeO₃

In recent years,with the development of industrial production and the improvement of people's living quality,the requirements for gas sensors accuracy,performance,stability are getting higher and higher in the fields of industrial production,family safety,health care and environmental monitoring.The exhaust gas of industrial production will cause serious environmental pollution and the petroleum gas and natural gas can cause explosion or poisoning,which require timely and effective monitoring the gases,so the research on gas sensor is getting more and more attention.In the past few decades,the study have found that a variety of metal semiconductor oxide showed a good gas sensitivity to some specific gas,but the operating temperatures are always pretty high,which are short of practicality.Perovskite-type semiconductor metal oxide?ABO₃?is an important functional material.Which are getting more and more attention by scientific research workers because of its unique structure and character in recent years.As a gas-sensitive material,perovskite-type semiconductor metal oxide has some special advantages that the single metal oxides haven't.,which shows a good gas-sensitive nature.Since the crystal structure of ABO₃ is very stable,we can dop other metal ions on A-bit or B-bit to improve its performance without change its crystal structure.In this paper,YbFeO₃ nanomaterials were prepared by sol-gel method and doped with different proportions of Ca and Pd,and the gas-sensing properties to acetone and CO₂ were systematically studied,which mainly include the following four aspects content:1.We prepared YbFeO₃ nanopowder material annealed at different temperatures?700?,800? and 900??.It was found from XRD that the orthorhombic perovskitestructure YbFeO₃ single phase only when the annealing temperature reached 900?,while the samples annealed at 700? and 800? exhibit a mixed phase of orthorhombic YbFeO₃ and hexagonal Yb2Fe3O7.YbFeO₃ is a typical p-type semiconductor,but YbFeO₃-Yb2Fe3O7 showed the characteristic of n-type semiconductor.We suggested that the adsorption of acetone will break the surface charge-related state of Yb2Fe3O7.In addition,the maximum responses to acetone at the optimum operating temperature of the materials annealed at 700 ?,800 ? and 900 ?are 1.105,1.12 and 1.082,respectively.The mixed phase samples of YbFeO₃-Yb2Fe3O7 annealed at 800 0 C for 5h showed the best response to acetone.The maximum sensitivity of 0.5,1 and 3 ppm acetone gas was about 1.12,1.21 and 1.42 at the optimal operating temperature of 250?.2.The effects of Ca doped YbFeO₃ on the gas sensing properties to acetone were systematically studied.It can be concluded that crystal structure of YbFeO₃ does not change when Ca element doped on the A-site.With the addition of Ca element,the unit cell volume of Yb_1-xCa_xFeO₃ nanocrystalline material becomes larger,The crystallite size decreased with the increase of the doping amount x,indicating that during the high temperature treatment,Ca2+ doping might have prevented the YbFeO₃ particle size from growing.In addition,the resistance of Yb_1-xCa_xFeO₃ material is greatly reduced with doping of Ca.With an increase of Ca content x,the resistances of sensors firstly decrease,undergo a minimum at approximately x = 0.1,and then increase again.The resistance of the Ybi-xCaxFeO₃ sensor is significantly increased after exposure to acetone gas and decreases after leaving acetone,which shows the typical characteristics of the p-type semiconductor sensor.The optimal operating temperature is 230? for all materials.At 230 ?,the response?Rg/Ra?of the material to 0.5 ppm acetone is of 1.66,2.32 and 1.26 for Yb_1-xCa_xFeO₃ at x = 0.1,0.2 and 0.3,respectively.Which indicates that the appropriate Ca substitution?about 20 at.%?for Yb in YbFeO₃ not only reduces the optimum operating temperature but also enhances the sensing response.When x=0.2,the material exhibits the highest response to acetone.What's more,the resistance of the Yb_0.8Ca_0.2FeO₃ sensor decreases as the relative humidity increases within the range of 13%to 45%.The response of the sensor to acetone gas increases with increasing relative humidity,especially when the relative humidity is higher than 22%.And the sensitivity response?Rg/Ra?of Yb_0.8Ca_0.2FeO₃ to acetone gas increases with the increase of acetone gas concentration.At the optimum working temperature?230??,the response for Yb_0.8Ca_0.2FeO₃ sensors to 0.05,0.1,0.5,1,1.5,2 and 3 ppm acetone were about 1.2,1.53,2.32,3.03,4.0,4.12 and 5.0,respectively.In addition,it was confirmed that Yb_0.8Ca_0.2FeO₃ shows good selectivity to acetone gas.3.The gas-sensing properties of Pd doped Yb_0.8Ca_0.2FeO₃ was studied.It was found that the doping of Pd can greatly improve the sensitivity of Yb_0.8Ca_0.2FeO₃ sensor to acetone,but excess doping could reduce the gas-sensing properties of the element.The Pd-doped Yb_0.8Ca_0.2FeO₃ of 3wt.%showed the highest the response to acetone gas.The maximum response of 3wt.%Pd-doped Yb_0.8Ca_0.2FeO₃ sensor to acetone increases with the increase of acetone gas concentration.The optimal temperature is also 230?.At 230?,the response of the sensor to 0.1 ppm,0.5 ppm,1 ppm,and 3 ppm acetone gas was 2.22,3.58,5.22 and 7.36,respectively.In addition,the effect of humidity on the gas-sensing performance of the sensor was also investigated.The response of 3 wt.%Pd-doped Yb0.sCa0.2FeO₃ to different concentrations of acetone increased with the increase of relative humidity.At a relative humidity of 54%,the response of sensor to 0.5 ppm,1 ppm and 3 ppm acetone can reach 3.86,7.12 and 9.52.4.The Yb_1-xCa_xFeO₃ annealed at 950? for 4 h was prepared and the gas-sensing properties of CO₂ were systematically studied.It was found that the optimal operating temperature of Yb_1-xCa_xFeO₃ with different Ca content was 260?.At 260?,the response Rg/Ra of the Yb_1-xCa_xFeO₃ sensor to 5000 ppm CO₂ is 1.216,1.529,1.852 and 1.248 when x = 0,0.1,0.2 and 0.3,respectively.When x = 0.2,the sensor showed the best response to CO₂.The maximum response Rg/Ra of the Yb_0.8Ca_0.2FeO₃ sensor to 1000 ppm,3000 ppm,5000 ppm,10000 ppm and 50000 ppm CO₂ is 1.278,1.769,1.852,2.056 and 3.815,respectively.In addition,with increasing of CO₂ concentration,the response time of Yb_0.8Ca_0.2FeO₃ becomes shorter and the recovery time becomes longer.And the response time and recovery time of Yb_0.8Ca_0.2FeO₃ decrease with the increase of operating temperature.As for humidity,the response of Yb_0.8Ca_0.2FeO₃ increases with the increase of humidity.When the relative humidity exceeds 16%,the change is especially obvious.When the humidity is 39%,The response of Ybo.s Ca0.2FeO₃ to 3000 ppm,5000 ppm,10000 ppm and 50000 ppm CO₂ can reach 1.315,1.584,2.012,2.294 and 3.951.