锂掺杂二氧化钛空/燃比厚膜材料的氧敏特性

OXYGEN-SENSING PROPERTIES INVESTIGATION OF LITHIUM-DOPED TITANIA THICK-FILM MATERIAL USED AS AIR/FUEL CONTROL SENSOR

研究了锂(Li)掺杂二氧化钛(TiO2)作为空/燃比控制用厚膜敏感材料的响应特性。X射线衍射分析表明:适量掺杂能保持TiO2厚膜的金红石结构,但晶胞参数有所增大。扫描电子显微镜显示:在摩尔分数(下同)为2%～4%范围内,TiO2厚膜晶粒没有明显变化。Kroger-Vink缺陷分析表明:锂离子主要以替位方式占据Ti的格点位置;600℃下样品呈p型半导体特性,电阻随氧分压增加而减小。伏安法测试结果显示:在一定Li掺杂范围内,既能提高样品响应特性和响应速率,又能扩展样品工作的温度范围(200～600℃),但较高Li(4%)掺杂导致样品的底电流增加而影响响应时间。结果显示:合适(3%)的Li离子掺杂,在金红石结构下增加晶胞参数,产生大量导电空穴,从而拓宽样品敏感温度的范围,增强氧气敏感特性。

The oxygen-sensing properties of lithium （Li） doped titania （TiO2） used as thick-film material of air/fuel （A/F） control sensor was investigated. X-ray diffraction analysis indicates that Li-doped TiO2 exhibits the presence of only rutile phase and enlarged crystal lattice parameters. The grain size of the material has no obvious change at 2%-4% （mole fraction, the same below） doping concentration, confirmed by scanning electron microscope. The Kroger-Vink model indicates that Li mainly substitutes the lattice point of Ti, and at 600 ℃, the Li-doped samples can be regarded as p-type semiconductors based on the change in resistance induced by oxygen. The samples show that Li doping can improve the response properties and response time, as well as expand the working temperature range （200-600 ℃）, confirmed by the voltammetry testing;however, high Li doping concentratios （4%） result in a heavy background current and affect the response time. The results indicate that the 3% Li-doped sample exhibits a broad sensing-temperature and the best response characteristics. The response mechanism is suggested to arise from the conduction hole ionized by Li under the enlarged crystal lattice parameters of rutile phase.