Gas-sensing And Piezoelectric Properties Enhanced By Polar Surfaces Of Iron Oxide And Barium Titanate And Their Mechanisms

In recent years,researchers have found that nanomaterials can significantly improve their photocatalytic and gas sensing properties by exposing their polar crystal faces.In this paper,hexagon α-Fe2O3 nanoplates exposed to {001} polar faces were prepared,and the gas sensing properties of the nanoplates were improved by surface hydrogenation.α-Fe2O3 hexagon nanoplates doped with Mn were prepared,the gas sensing properties were improved by hydrogen treatment.The gas sensing properties were also improved by hydrogen treatment in the preparation of BaTiO3 microplates and nanowries exposed to {001} polar crystals.The correlation between the gas sensing properties and the surface structure of the prepared microplates was studied,and the concept of reactive sites and the corresponding gas sensing mechanism were proposed,the mechanism of gas sensing at the atomic and molecular level is described.The main research are as follows:（1）α-Fe2O3 hexagon nanoplates materials with exposed polar crystal plane of{001} were prepared by solvothermal method.The surface of the nanoplate was treated in hydrogen atmosphere at different temperatures to obtain the hydrogenated nanoplate.Methanol,triethylamine and ethanol gas were tested for the five products,and it was found that the hydrogenated products had high response in the three test gases.The effect of {001} crystal plane and hydrogen treatment on the reaction was investigated,and the surface structure of the sample was analyzed.It was found that there were reactive centers on {001} crystal plane,namely,Fe atoms with dangling bond unsaturated 3-coordination.Its main functions include:adsorbing oxygen from air,the production of free electrons and catalysis.This not only provides a new idea for material sensing and catalytic reaction,but also provides a technical guidance for designing high-performance materials.（2）Mn selectively doped to {001} crystal plane was prepared by solvothermal reaction.The selective doping of Mn can increase the proportion of the polar crystal plane of {001} and make the sheet thinner,the Mn doped nanosheets were then treated with hydrogen gas.The sensing properties of n-butylamine,acetone and ethanol were tested on seven samples.It was found that Mn can improve the sensing properties when Mn is selectively doped to {001} polar crystal plane,the sensing performance of Mn-doped nanoplates after hydrogenated treatment was further improved.The doping of Mn element and the effect of {001} crystal plane are studied.It is found that Mn element is selectively doped to {001} crystal plane.This doping can increase the proportion of {001} polar crystal plane,at the same time,the unsaturated 3-coordinated Fe atoms with dangling bonds on the surface of（001）are still the active center of the reaction.It is further proved that the hydrogen permeation reaction can provide a new idea and method for the preparation of high performance materials.（3）BaTiO3 microplates and nanowries exposed to {001} crystal plane were prepared by molten salt method.The results show that the gas sensing properties of BaTiO3 microplates and nanowries with large proportion of crystal plane are the best,and then the gas sensing properties of BaTiO3 microplates are further improved by hydrogenation.The atomic structure of tetragonal BaTiO3 {001} crystal plane and the effect of hydrogen treatment were investigated.It was found that the tetragonal BaTiO3{001} crystal plane was polar and the Ba atom was the reactive center.This method provides a basis for the design of new sensors,catalysts and other performance materials.（4）The BaTiO3 ceramics with different texture coefficients were prepared by solid-state method,and the piezoelectric properties of BaTiO3 ceramics with the largest texture coefficients were found to be the best.The piezoelectric properties of BaTiO3 ceramics were further improved by polarization treatment.The relationship between the piezoelectric properties and the texture coefficient was studied,and the relationship between the piezoelectric properties and the BaTiO3 ceramics with higher texture coefficient was summarized.