Synthesis And Gas-humidity Sensing Properties Of Perovskite BaTiO₃ And Cs₂SnX₆

The sensor based on perovskite nano materials has excellent sensing performance,and can detect small molecules such as oxygen,nitrogen dioxide or carbon dioxide.In order to develop gas and humidity sensors with low temperature,low power consumption and high performance,we can consider forming nano materials with perovskite structure or synthesizing new perovskite materials.Barium titanate(BaTiO₃)is a typical perovskite structure ceramic material,which has been proved to be an excellent impedance humidity sensing material,yet the corresponding application of human respiratory monitoring has not been reported.Moreover,the all-inorganic Sn based halide perovskite Cs₂Sn X₆(X=Cl,Br and I)is lead-free,non-toxic,good stable in air,and not easy to oxidize in the presence of Sn⁴⁺.Meanwhile,Cs₂Sn X₆ materials have not been applied to gas sensors.This paper mainly includes three parts.Firstly,BaTiO₃ nanostructures with different morphologies were synthesized by simple and controllable molten salt method.The humidity sensitivities were researched and applied to respiratory monitoring.Then,Cs₂Sn Cl₆ with different hydrochloric acid(HCl)concentrations and Cs₂Sn X₆(X=Cl,Br and I)with different halogen elements were synthesized by simple and reliable room temperature liquid phase synthesis.And the gas sensing properties were researched respectively.The specific results are as follows:1.BaTiO₃ nanostructures including nanobelts,nanowires and nanoparticles,were successfully synthesized by molten salt method.As a humidity sensitive material,the synthesized BaTiO₃ nanostructure had higher response value and shorter response time than commercial BaTiO₃.In particular,the BaTiO₃ nanobelts humidity sensor held good response(S_r=1.82×10³),the shortest response/recovery times(1 s/22 s)and the smallest hysteresis(?H=0.67%).Excellent sensing performance can be attributed to the synergistic effect of the large specific surface area and small pore size.In addition,the BaTiO₃ nanobelts humidity sensor showed considerable potential in the field of human respiratory monitoring.This work provides a new perspective to high-performance humidity sensors for human body-related detection through morphology-controlled perovskite nanostructures.2.Four kinds of Cs₂Sn Cl₆ with different HCl concentrations were successfully synthesized by room temperature liquid phase synthesis.The sensing performance of Cs₂Sn Cl₆ were researched through gas sensitivity tests.The results showed that the Cs₂Sn Cl₆-10 sensor had good selectivity and high sensitivity to 200 ppm formaldehyde(HCHO)at the optimal working temperature of 160?(S_r=114),fast response/recovery times(9.6 s/12 s),good reproducibility and long-term stability.Excellent sensing performance can be attributed to the synergistic effect of material Cs₂Sn Cl₆-10 with larger S_A and better stability due to more Sn⁴⁺content.More Sn⁴⁺content will reduce the amount of O₂ adsorbed by competition,so that more target gas HCHO molecules can be adsorbed.Therefore,considering the advantages of halide perovskite Cs₂Sn Cl₆ non-toxic,harmless,good air stability,high sensitivity and selectivity.It can be widely used in HCHO gas sensor,which opens up a way for the research of new sensing materials.3.Three kinds of Cs₂Sn Cl₆,Cs₂Sn Br₆ and Cs₂Sn I₆ with different halogen elements were successfully synthesized by room temperature liquid phase synthesis,and their gas sensing properties were researched respectively.The results displayed that the Cs₂Sn I₆ sensor had excellent selectivity for 100 ppm HCHO at room temperature,ultra-high response value(S_r=78),short response/recovery times(?3.6 s/3.6 s),good repeatability and long-term stability.Excellent sensing performance was due to the large specific surface area and large pore size of Cs₂Sn I₆,which provides more active sites and more allowable gas adsorption capacity for gas adsorption.Therefore,based on halide perovskite Cs₂Sn I₆ has excellent properties such as lead-free,non-toxic,good air stability,high sensitivity and rapid response at room temperature.It will have a far-reaching impact on the field of gas sensors widely used to detect HCHO concentration at room temperature in the future.