【作者】 董亮；

【导师】 王豫；

【作者基本信息】 西南交通大学 ， 材料学， 2011， 博士

【摘要】 WO3是一种重要的高技术原材料,在低压压敏变阻器、电致变色、有毒气体探测和光降解催化等方面具有巨大的应用潜力。W03的分子式比较简单,但是由于其复杂的结构和组分变化,物理性质尤其是电学性质比较复杂,深入系统研究钨基氧化物的物理性质,对深层次开发我国的特色资源,具有重要的意义。前期的研究发现,前驱体微米化的钨基陶瓷在室温下相共存现象严重,这导致陶瓷的电学行为不稳定,初步实验研究发现前驱体纳米化后烧结的陶瓷在室温下是单相结构。因此本文以纳米W03粉作为前驱体,对钨基功能陶瓷的电学性质进行研究,结合国家自然科学基金的内容,尤其对中高温温区内的电学行为进行了系统研究,本文的研究内容可以丰富我们对钨基功能陶瓷电输运过程的认识。本文采用沉淀法和溶胶-凝胶法两种方法分别制备了纳米化WO3粉末,并以此为前驱体制备了不同条件的钨基陶瓷,两种制备方法制备的前驱体粉末在相同的条件下制备的陶瓷有很大的差别,文中给出了在1000℃C烧结1小时的实验结果,室温下电阻率分别为分别为1.05×104Ω.cm和51Ω-·cm,相差2000倍,XRD分析表明陶瓷中WO3的主晶相有很大差别。根据实验中所用前驱体的不同,本文的主要工作分为两大部分：第3章中,首先用沉淀法制备了纳米WO3粉,以此为前驱体研究了热处理温度和热处理时间以及Ce掺杂对其电学行为的影响。对陶瓷XRD的分析表明,1000℃烧结的陶瓷,室温下主晶相是单斜相；对热处理温度的研究表明700℃-900℃是一个重要的烧结区间,在此区间样品的晶粒迅速长大；文章给出了简单的前驱体纳米化后钨基陶瓷烧结过程中晶粒长大的动力学模型,计算了晶粒长大的激活能,前驱体纳米化后纯的WO3陶瓷晶粒长大的激活能为43.94kJ/mol,Ce掺杂样品的激活能为103.3kJ/mol,表明掺杂对晶界的迁移有阻碍作用,晶粒长大的激活能变为原来的2倍多；同一温度下不同烧结时间的研究发现,烧结时间在8小时以内,热处理温度为600℃和1000℃的条件下,烧结时间对纯WO3陶瓷晶粒的形状和大小影响不大,1000℃下烧结时间对晶界具有一定的贡献,低温下烧结时间对样品电学行为影响不大；600℃烧结的样品,室温下伏安特性为线性,随着测试温度的升高,在100℃时开始出现非线性,论文中用氧吸附和氧空位的理论对此进行了解释。第4章中,采用课题组成员郭娜发明的溶胶-凝胶法制备了纳米WO3粉,以此为前驱体研究了1000℃烧结的纯WO3陶瓷以及纳米Nd2O3和Dy2O3掺杂的钨基陶瓷的电学行为。对1000℃烧结的纯的WO3陶瓷进行XRD分析,表明室温下陶瓷的主晶相为WO3的三斜相,此时样品的电导率与WO3微晶本身的电导率相近；前驱体纳米化后Nd2O3和Dy2O3的掺杂表明,小比例掺杂下,样品的电学行为主要反映WO3的性质,大比例掺杂的情况下,在晶界处产生了新的物相,此时样品低电场线性区的电学行为主要反映晶界的电学特性,大比例掺杂样品的非线性电学行为归结为晶界处的肖特基势垒,此时由于新的物相处于晶界处,样品的氧吸附很难形成。第5章中,对钨基氧化物陶瓷的电学行为进行了一些简单的分析。更多还原

【Abstract】 Tungsten trioxide (WO3) has received more attention because of its potential for many technology applications, such as varistors、electrochromic devices、gas sensors and photocatalytic degradation. The molecular formula of WO3is quite simple, but its electrical properties is complex, because that it undergoes several well-characterized phase transitions at different temperature and many intermediary suboxide. More importantly, the deep research about tungsten is lagged behind other countries such as the Occident and Japan. So it has scientific and practical significant to investigate the physical properties of tungsten oxide. Many investigations discovered that the electrical properties of sintered WO3ceramics are instable which lead to the coexistent of phase at room temperature. We found that the WO3ceramics prepared by nano-powders have only one phase. The electrical properties of WO3ceramics which prepared by nano-powders were studied in the room-to-high temperature range, combining with the National Natural Science Foundation of China. The research will enrich us to understand the electrical transport process.In this article, WO3namopowders have been prepared by precipitation method and sol-gel method, and prepared WO3ceramics by using nanopowders. We found the resistivity is1.05×104Ω·cm and51Ω·cm respectively at room temperature, and the analysis of the XRD indicated that the phase is different. In our present work, the article has two parts for two namopowders.In Chapter3, WO3nanopowdcrs were prepared by precipitation method. Effect of sintering temperature、sintering time and Ce-doped on electrical properties of WO3ceramics prepared by nanopowders was studied in detail. The XRD indicated the WO3ceramics which sintered at1000℃for1hour are monoclinic phase; and this is an important temperature section from700℃to900℃, the grain of samples rapidly grow up. A simple kinetics model of grain growing is established and the grain growth activation energy is calculated. The grain growth activation energy of pure WO3ceramics is43.94KJ/mol,and that doped by Ce is103.3KJ/mol, so the doping has hindered the migration of the grain boundaries; and we found that sintering time has little effect on the shape and size of the grains, the sintering time has made some contribution to the grain boundary at1000℃, the sintering time has little effect on electrical behavior of the samples sintered at600℃; the voltage-current characteristic of the samples sintered at600℃is the linearity at room temperature, and which is nonlinear at100℃, in this paper, we explain the change of the voltage-current characteristic of the samples sintered at600℃at different temperature with the oxygen adsorption and the oxygen vacancy.In Chapter4, WO3nanopowders were prepared by sol-gel method, the pure WO3ceramics and Dy2O3、Nd2O、3-doped WO3ceramics were prepared by the conventional solid state reaction at1000℃using nm-level powders, and the electrical properties of the samples were studied. The main phase of undoped WO3ceramics sintered at1000℃is triclinic,and the conductivity is higher, the measured conductivity is close to the specific conductivity of WO3crystallites. The electrical property of the samples doped by Dy2O3and Nd2O3is similar, when the amount of Dy2O3and Nd2O3is small, the voltage-current characteristic is the linearity,which is accord with the pure WO3ceramics, the new crystal boundary will appear with increasing Dy2O3and Nd2O3, and the voltage-current characteristic is a nonlinearity, which can be expained by Schottky barriers at grain boundary.In Chapter5, the analysis on the electrical behavior of WO3ceramics was explained simply.更多还原