Morphology-Controlled Preparation And Ethanol Gas-Sensing Performance Study Of Indium Oxide Materials

Semiconductor metal oxide indium oxide（In₂O₃） is an important and multifunctional material. It has been widely used as solar energy cell, transparent electrode, photoelectronic sensor, electrostatic resistance coating and gas sensor due to its excellent physical and chemical properties. As a gas-sensing material, the sensing characteristics of In₂O₃ strongly depend on its size and structure, such as grain size, crystal facet, specific surface area, dimensionality, network, porosity and dopants. In this dissertation, In₂O₃ nanoparticles, cubes and octodecahedra were controllably prepared by annealing the corresponding In（OH）₃ precursor synthesized hydrothermally. Meanwhile, the effects of particle size and different arrangements of atom In and O on {100} and {110} facets on the formation of oxygen vacancy were investigated systemically as well. The influences of oxygen vacancy and exposed crystal facet on gas-sensing performance were disclosed. The main research contents are as follows:In₂O₃ nanoparticles with different size are prepared and the effects of grain size on sensitivity, response/recovery time, stability are studied in detail. In（OH）₃ nanoparticle precursors with different sizes are controllably prepared via hydrothermal process by using indium chloride tetrahydrate as In source and aqueous ammonia and hydrochloric acid to adjust p H value of the reaction solution as 7, 9, 11. The In₂O₃ particles with different sizes are obtained by annealing the corresponding In（OH）₃ precursor. The gas-sensing performances of In₂O₃ with different sizes are studied. The effects of particle size on oxygen vacancy contents of the surface and gas-sensing property are deeply discussed. The amounts of oxygen vacancy on the surface have an important effects on gas-sensing performance. The relationship between oxygen vacancy concentration and gas-sensing performance are disclosed. The discussions mainly focus on the relationship among particle size, oxygen vacancy contents and gas-sensing mechanism of different sensitivity resulting from In₂O₃ nanoparticle with different sizes.For In₂O₃ cubes, when the particle size are nearly the same and all exposed crystal facet are {100}, the factors affecting sensitivity are studied. In（OH）₃ cube with comparative size and exposed {100} facet are controllably synthesized via a hydrothermal process by using indium chloride tetrahydrate as In source and tetraethylammonium hydroxide, tetramethylammonium hydroxides and urea as base source. The In₂O₃ cube exposing {100} facet are acquired by annealing the corresponding In（OH）₃ cube precursor. The effect of surface defect on gas-sensing properties are studied by using cube prepared from different base sources as a model except for the influence of particle size and exposing crystal facet on gas-sensing properties. The influence of subsurface oxygen vacancy contents on gas-sensing performance are analyzed according to the crystal structure of material, and the relationship between surface defect and gas-sensing performance are further obtained. The effects of different base sources on the creation of subsurface oxygen vacancy contents and gas-sensing performance are disclosed. The arrangements of In and O atoms on {100} facet, the formation of subsurface oxygen vacancy and gas-sensing performance are further discussed.For In₂O₃ octodecahedra, the effect of exposed high energy {110} facet on gas-sensing performance is investigated. In（OH）₃ octodecahedra exposing {110} and {100} facets are controllably synthesized via hydrothermal process using indium chloride tetrahydrate as In source and adjusting the amount of base source Na OH and the volume ratio of absolute ethanol to deionied water in reaction medium. The effect of the amount of base source Na OH,different volume ratio of absolute ethanol to deionied water in reaction medium and reaction time on the formation of In（OH）₃ octodecahedra are detailedly studied and a possible growth mechanism are proposed. In₂O₃ octodecahedra exposing {110} and {100} facets are obtained by annealing the corresponding In（OH）₃ octodecahedra. The effect of oxygen vacancy contents on different crystal facet on gas-sensing performance is studied according to the crystal facet analysis, and the relationship among exposed high energy facet, formation of oxygen vacancy and gas-sensing performance are further discussed. The different arrangements of In and O atoms on {100} and {110} crystal facets have an important effect on the creation of oxygen vacancy. The relationship of exposed crystal facet, material structure and sensing characteristics are constructed.