【作者】 付东升；

【导师】 强亮生； 郝素娥；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2013， 博士

【摘要】 随着导电粉应用领域的不断拓宽，国内外诸多学者致力于提高导电粉导电性研究。掺杂稀土元素既可以提高粉体的导电性能，又可以改善粉体的介电性能，已成为粉体改性研究的热点。采用溶胶-凝胶法制备了BaTiO₃、Na_0.5Bi_0.5TiO₃和Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃粉体。通过讨论溶胶pH值、反应温度和热处理温度等条件对Na_0.5Bi_0.5TiO₃和Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃粉体结构、形貌、电阻率和介电常数的影响，确定了制备Na_0.5Bi_0.5TiO₃优化的工艺条件为：溶胶体系pH=3.5，反应温度20℃，烘干温度150℃，热处理温度350℃，煅烧温度700℃。所得Na_0.5Bi_0.5TiO₃粉体的平均晶粒为50nm，室温电阻率为3.71×106Ω m，频率500Hz时的介电常数εr为393.21，且在高频区内介电损耗比较稳定。以柠檬酸作为螯合剂制备Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃粉体的优化工艺条件为：溶胶体系pH=4.5，反应温度为40℃，烘干温度为120℃，热处理温度为500℃，煅烧温度为750℃。针对不同x值（x0,1）所制备的Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃粉体中，随着x值增大，电阻率呈下降趋势，其中Ba_0.2(Na_0.5Bi_0.5)_0.8TiO₃粉体室温电阻率最低，达3.24×107Ω m。在制备纯BaTiO₃和Na_0.5Bi_0.5TiO₃粉体的基础上，为进一步降低其电阻率，采用液相掺杂方法对BaTiO₃和Na_0.5Bi_0.5TiO₃粉体进行了稀土改性研究。选择稀土元素Sm、Ce、Pr和Gd进行了液相掺杂实验研究。电阻率测试结果表明，稀土元素液相掺杂可以降低粉体的电阻率，其中Sm掺杂对降低BaTiO₃和Na_0.5Bi_0.5TiO₃粉体电阻率最为明显。Sm掺杂使BaTiO₃粉体的电阻率从4.30×10⁹·m降低至2.38×10⁶·m。选择Sm元素进行了不同Sm掺杂量改性Na_0.5Bi_0.5TiO₃实验研究，Na_0.5Bi_0.5TiO₃的电阻率随Sm掺杂量的增加呈现先降后升的趋势。当Sm的掺杂量为0.5at%时，Na_0.5Bi_0.5TiO₃粉体的电阻率最低，达2.41×10⁵Ω m。介电性能测试表明，Sm掺杂使Na_0.5Bi_0.5TiO₃的介电常数增大，介电损耗随频率变化的趋势与纯Na_0.5Bi_0.5TiO₃粉体相同。XRD分析结果表明，Gd、Pr和Sm均掺入到A位。SEM表征表明，稀土元素掺杂可使粉体粒径减小，部分粉体颗粒出现团聚现象。XPS分析测试表明，稀土掺杂后粉体表面富集Na元素，并形成了非化学计量表面层。统筹考虑电性能测试和形貌分析的实验结果，选择Sm元素进行了气相扩渗实验。制备了不同温度Sm气相扩渗改性BaTiO₃、Na_0.5Bi_0.5TiO₃和Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃粉体，并讨论了改性前后BaTiO₃、Na_0.5Bi_0.5TiO₃和Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃粉体组成、结构和电性能上的变化。研究结果表明，Sm扩渗改性能降低BaTiO₃、Na_0.5Bi_0.5TiO₃和Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃粉体的电阻率，且在一定温度范围内（740℃⁸60℃），电阻率随着扩渗温度的升高而降低。当扩渗温度为860℃时，Sm扩渗改性后，Na_0.5Bi_0.5TiO₃粉体电阻率从3.71×10⁶Ω m降为4.01×10⁵Ω m；BaTiO₃粉体电阻率从4.3010⁹Ω m降为4.27×10⁴Ω m； Ba0.6（Na0.5Bi0.5）0.4TiO3粉体电阻率从5.76×10⁸Ω m降为3.67×10³Ω m。采用Materials Studio软件对Gd、Pr和Sm掺杂的BaTiO₃和Na_0.5Bi_0.5TiO₃体系进行了计算。计算结果表明，A位和B位掺杂均使BaTiO₃和Na_0.5Bi_0.5TiO₃体系晶胞发生畸变，而且A位掺杂后体系单点能更低，更稳定，说明BaTiO₃和Na_0.5Bi_0.5TiO₃体系更倾向于A位掺杂。Gd、Pr和Sm降低BaTiO₃和Na_0.5Bi_0.5TiO₃粉体电阻率的原因是在能带中引入了杂质能级，减小了禁带宽度，从而改善BaTiO₃和Na_0.5Bi_0.5TiO₃粉体的导电性，计算结果和实验数据基本吻合。更多还原

【Abstract】 The conductive powders have attracted considerable attention in recent yearsbecause of their very important applications in many fields especially in staticelimination. Rare earth modified method can improve the conductivity and thedielectric properties of powders, and become the hot research of powder modified.In this study, BaTiO₃, Na_0.5Bi_0.5TiO₃and Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃powders wereprepared by the sol-gel method. The process conditions of preparing Na_0.5Bi_0.5TiO₃and Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃powders such as pH, reaction temperature and heattreatment temperature were studies. The effects of the process conditions on powderstructure, morphology and resistivity, dielectric constant effects of Na_0.5Bi_0.5TiO₃and Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃powders were discussed to find the optimum processconditions. The optimum process conditions are as follows: pH=3.5，reactiontemperature of20℃, drying temperature of150℃, warm-up temperature of80℃,calcining temperature of700℃. The Na_0.5Bi_0.5TiO₃powders with an average grainsize of50nm，has the room temperature resistivity of3.71×10⁶Ω m, the frequency of500Hz, the dielectric constant εr393.21, and its cut dielectric loss in the highfrequency region is relatively stable. The optimum process conditions of preparingBa_（1-x）(Na_0.5Bi_0.5)_xTiO₃powders with citric acid as a chelating agent are as follows:pH=4.5，reaction temperature of40℃, drying temperature of120℃, warm-uptemperature of5000℃, calcining temperature of750℃. The resistivity of theBa_（1-x）(Na_0.5Bi_0.5)_xTiO₃powders decreases with the increases of x, and reached thelowest point of3.24×10⁷Ω m with the values of x was0.8.Based on obtained pure BaTiO₃and Na_0.5Bi_0.5TiO₃powders, the liquid-phasedoping technique was adopted to improve the conductivity of the BaTiO₃andNa_0.5Bi_0.5TiO₃powders. The resistivity of Sm-dopped BaTiO₃and Na_0.5Bi_0.5TiO₃powders are much lower than the other rare earths dopped powders. When theconsistency of Sm is0.3at%, the resistivity of Sm-dopped BaTiO₃powder is thelowest, which drops from4.30×10⁹Ω m to2.38×10⁶Ω m. When the consistency ofSm is0.5at%, the resistivity of Sm-dopped Na_0.5Bi_0.5TiO₃powder is the lowest,which drops from3.71×10⁶Ω m to2.41×10⁵Ω m. The result of dielectric testsshowed that Sm-doping method improved the ceramic dielectric constant, and thedielectric loss versus frequency of Sm-dopped Na_0.5Bi_0.5TiO₃and pure Na_0.5Bi_0.5TiO₃have essentially the same changing tendency. The result of XRD analysis showedthat Gd, Pr and Sm were incorporated into the A site. The result of XPS analysisshowed that the powder surface after rare earth doping enriched Na elements, and non-stoichiometric surface layer was formed.Combined with electrical properties and morphology analysis of theexperimental test results, the gaseous penetration experiments was done by usingSm elements as diffusion agent。The composition, structure and conductivity of theSm-penetrated BaTiO₃, Na_0.5Bi_0.5TiO₃and Ba_（1-x）(Na_0.5Bi_0.5)_xTiO₃powders beforeand after doping were studied. The results reveals that the powder resistivity dropswith the increase of penetration temperature. The resistivity of Sm-penetratedBaTiO₃powder drops from4.30×10⁹Ω m to4.27×10⁴Ω m. The resistivity ofSm-penetrated Na_0.5Bi_0.5TiO₃powder drops from3.71×10⁶Ω m to4.01×10⁵Ω m.The resistivity of Sm-penetrated Ba0.6（Na0.5Bi0.5）0.4TiO3powder drops from5.76×10⁸Ω m to3.67×10³Ω m.The first-principles calculation was carried out with Materials Studio softwarepackage for Gd, Pr and Sm-modified BaTiO₃and Na_0.5Bi_0.5TiO₃system. The resultsshow that dopant elements render crystal cell distorted. After comparison ofsingle-point energy between A-site substitution and B-site substitution, it is foundthat rare earth elements are relatively easy to substitute A site. Impurity levels areintroduced within the band gap or overlap with the band edge of the BaTiO₃andNa_0.5Bi_0.5TiO₃structures and leading to band gap narrowing, which results in thereduction of the resistivity of the rare earth elements-modified BaTiO₃andNa_0.5Bi_0.5TiO₃system. By the analysis of calculation results and experimental data,it is found that they match with each other and will be helpful for future research.更多还原