【作者】 殷立雄；

【导师】 黄剑锋；

【作者基本信息】 陕西科技大学 ， 材料物理与化学， 2012， 博士

【摘要】 氧化钐（Sm₂O₃）是一种具有4f电子结构的宽禁带金属氧化物，常温下禁带宽度为4—6eV，Sm₂O₃晶体具有三种晶型，当温度高于850℃时，单斜晶相转变为立方晶相，在2000℃左右转变为六方晶相，属于多晶相转化的氧化物，氧化钐具有高的电阻率，高的介电常数，高的化学稳定性和热稳定性等性能，具有优越的电学、光学和磁学性能，广泛应用于陶瓷电容器、汽车尾气处理、催化剂和医学等方面；另外，纳米Sm₂O₃还具有核性质，可用作原子能反应堆的结构材料、屏蔽材料和控制材料等领域。本研究采用SmCl₃·6H₂O和Sm（NO₃）₃·6H₂O为起始原料，在水热法、溶剂热法条件及模板剂辅助条件下对Sm₂O₃纳米材料的合成工艺进行了系统的研究，制备出Sm₂O₃纳米晶，采用XRD、SEM、UV-vis等测试手段对纳米晶进行结构与性能的表征，系统研究了氧化钐纳米晶的合成条件对产物结构及光学性能的影响；揭示出水热温度、水热时间、前驱液浓度、pH值、模板剂的种类等，以及溶剂热的溶剂种类、溶剂配比、模板剂的种类对Sm₂O₃纳米晶晶体结构及形貌的影响规律。此外，通过控制反应条件（反应温度、时间、pH值、前驱物浓度、钐源、溶剂/水体积比例和不同模板剂等）对最终煅烧产物进行了物相晶体结构和形貌的可控制备。主要研究内容和成果如下：以SmCl₃·6H₂O和Sm（NO₃）₃·6H₂O为起始原料，采用水热法制备出纯相Sm₂O₃粉体。通过控制不同水热反应温度、前驱物的浓度、前驱液pH值、水热反应时间以及钐源等工艺因素，对水热体系下合成工艺参数对产物的物相、形貌和反应机理等进行了研究。采用XRD，SEM对纳米晶进行了系统的表征。结果表明，对于单斜相Sm₂O₃纳米棒状粉体，其最佳制备工艺为以SmCl₃·6H₂O为前驱体，水热反应在200oC温度，将前驱液浓度控制在0.4M，其pH值等于9的条件下反应48h，可得到尺寸均一，分散性好，结晶性强的纳米棒状Sm₂O₃粉体；前驱物浓度为1.0M，其他工艺因素不变时，得到性状良好的立方相Sm₂O₃粉体。通过对不同工艺因素的研究可知，水热反应产物物相与形貌对于最终煅烧产物的物相形貌等有着显著影响，而对于不同工艺参数的改变，其前驱物水解反应也随之变化，最终影响产物的物相与形貌。水热温度、前驱液浓度和pH值以及钐源对前驱物发生的水解反应有着较大影响，最终改变了产物的晶体结构，而前驱物浓度、钐源以及水热反应时间主要影响产物的结晶过程，对其最终形貌影响较大。通过研究在异丙醇、乙二醇以及乙醇体系中不同有机溶剂与水体积含量比例对产物物相和形貌的影响，对Sm₂O₃纳米粉体进行了系统的物相与形貌的可控制备，研究了不同溶剂体系下Sm₂O₃粉体的合成反应机理。结果表明，采用不同有机溶剂均可得到纯相的单斜相Sm₂O₃粉体，但该产物的形貌则有着明显区别。与水热体系中结果相比，在异丙醇体系中所得最终产物结晶取向性明显降低，同样的结果在乙二醇与乙醇体系中也可发现。此外，对于立方相Sm₂O₃粉体，采用纯乙醇体系进行溶剂热反应，可以得到纯度较高的目标产物。在异丙醇体系中，立方相产物仅在异丙醇与水混合体系中存在，而在乙二醇体系中则不能得到立方相产物。这说明立方相Sm₂O₃作为介稳态晶体结构，其对反应溶剂以及溶剂比例十分敏感，通过对比溶剂间性质区别推测溶剂极性以及溶剂分子的位阻因素可能为影响产物物相与结晶的主要影响因素。对水热/溶剂热体系下模板剂对Sm₂O₃物相和形貌的影响进行了研究。针对水热/溶剂热两种体系下产物的反应机理不同，采用不同模板剂对产物的形貌进行了尺寸和形状的可控制备。结果表明，在水热体系中，柠檬酸三钠、PVP、乌洛托品和草酸的加入有助于立方相的Sm₂O₃的形成，其对应形貌的取向性较低，主要为纳米球状和无规则颗粒状结构。CTAB、EDTA和NaNO₃的加入则会得到纯相的单斜相Sm₂O₃粉体，其形貌主要为纳米棒状结构。该棒状结构的直径，长度则依模板剂的不同而变化。在溶剂热体系中，加入羧甲基纤维素钠作为模板剂时，所得产物为纯相的单斜相Sm₂O₃结构。除此以外，CTAB、PEG-4000和油酸的加入，都会得到含有较多立方相Sm₂O₃的混合产物。在溶剂热体系中加入模板剂后所得产物均有显著变化，加入CTAB后可得到短棒状和六方片状混合产物形貌；羧甲基纤维素钠的加入可得到均匀纳米球状颗粒；PEG-4000和油酸的加入则会得到棒状与无规则颗粒状混合的产物形貌。通过不同模板剂在溶剂热体系中所得物相与形貌特征，分析了模板剂在产物结晶成核过程中的影响，揭示出模板剂影响最终产物形貌的生长机理。对于在水热/溶剂热条件下制备的不同形貌的Sm₂O₃粉体进行了紫外可见光吸收光谱的表征，并对具有不同形貌的Sm₂O₃粉体进行了禁带宽度的计算。结果表明，水热条件下添加不同模板剂所得产物的紫外-可见吸收光谱中的吸收曲线大致走向相同，在200—250nm的紫外区域内具有较强的吸收能力，最强吸收峰位于230nm处附近，在410nm处的可见光区域内还存在一个较弱的吸收峰。从紫外-可见吸收光谱分析可以发现，溶剂热条件下所制备产物的吸收曲线大致形状相同，在200—280nm的紫外区域内具有较强的吸收能力，最强吸收峰位于230—250nm处附近，在410nm处的可见光区域内还存在一个较弱的吸收峰。不同粒径和微观结构的Sm₂O₃粉体材料，因具有不同的量子尺寸效应和颗微观内应力，其所表现得光学性能中的禁带宽度也随之不同，从4.820eV变化至4.928eV。更多还原

【Abstract】 As a typical kind of metal oxides with4f electronic structure, three crystalphases are found in Sm₂O₃materials, of which the band gaps range from4to6eV. Sm₂O₃is a multiphase oxide which is found transiting from the monoclinicphase to cubic phase at850℃and then to hexagonal phase at2000℃. Theyhave been deeply studied for their high resistivity, dielectric constant chemicalstability and thermal stability with excellent electrical, optical and magneticproperties, which are considered to be widely used in fields including ceramiccapacitor, samarium metal preparation, automobile tail gas treatment, catalystsand medical treatments; Besides, Sm₂O₃materials are also found to have nuclearproperties to be used as structure, shielding and controlling materials of theatomic furnaces. Herein, hydrothermal and solvothermal methods with varioustemplates were employed to prepare Sm₂O₃microcrystals, of which the Smsources were SmCl₃·6H₂O and Sm（NO₃）₃·6H₂O. The synthesis process weresystematically investigated by using XRD, SEM and UV-Vis to characterize theproducts crystal structure and corresponding properties; The influences ofhydrothermal temperature, reaction time, precursor concentration, pH value ofthe precursor solutions, different Sm sources, templates, reaction solvents andratio between solvent and templates were completely investigated to control thecrystal structure and morphologies of the calcined products. The following arethe main research contents and results: Pure Sm₂O₃particles were successfully prepared by using SmCl₃·6H₂O andSm（NO₃）₃·6H₂O as the start materials. By changing the reaction temperature,precursor concentration, precursor solution pH value, reaction time and Smsources, the synthesis process were systematically controlled to study the productphase, morphologies and reaction mechanisms. XRD and SEM were used for thecharacterization. Results show that under the optimum reaction conditions （Smsources: SmCl₃·6H₂O; Reaction temperature:200oC; Precursor concentration:0.4M; pH value:9; Reaction time:48h.）, monoclinic Sm₂O₃particles with goodcrystallinity and dispersing properties are obtained. When the precursor ischanged concentration to1.0M, the as-obtained products present a crystal phaseof cubic Sm₂O₃with nanorod-like microstructure. By studying the influences ofdifferent reaction conditions, it is found that the calcined product phase andmorphology are greatly influenced by the hydrothermal products. Differentreaction temperature, precursor concentrations, pH values and Sm sources arefound to influence the product crystal structure; while the precursorconcentration, Sm sources and reaction times are found to have great effects onthe products morphologies.By studying influences of different organic solvent ratio on the productphase and morphology, the Sm₂O₃nanoparticles were systematically preparedwith controllable phases and morphology to investigate the Sm₂O₃reactionmechanism. Results show that monoclinic Sm₂O₃particles could be obtained indifferent solvent conditions with obvious morphology changes. It is found thatthe crystal orientation of the as-obtained product decrease clearly in isopropylalcohol system. Same results were found in both ethylene glycol and alcoholsystem. Besides, cubic Sm₂O₃particles could be obtained in pure alcoholcondition with high productivity. This phase could be also found in mixture ofisopropyl alcohol and water system, rather than in ethylene glycol, which suggestthat the cubic Sm₂O₃possess a metastable crystal structure with high sensitivityto solvent content. Comparing the different properties of these solvents suggeststhat the polarity and the molecular hindering effect of different solvents may bethe main influence factors when changing product phases and crystallizations.The influences of different hydro/solvothermal templates on the productphase and morphology were investigated. Aiming at the differences of the reaction mechanism between hydrothermal and solvothermal system, differenttemplates were employed to control the size and shape of the products. Theresults show that, under hydrothermal conditions, trisodium citrate, PVP,urotropin and oxalic acid may give rise to the formation of cubic Sm₂O₃phasewith low growth orientation, spheres-like and irregular particle morphologies.However, CTAB, EDTA and NaNO₃lead to the formation of monoclinic Sm₂O₃rods, which diameter and length that varies with different templates. Theproducts from solvothermal conditions are found more sensitive to the change oftemplates, which exhibit various morphologies: Mixed short rod and hexagonalsheet-like structure with CTAB as the template; Uniform spheres-likenanoparticles with carboxymethylcellulose sodium; Mixed rods andirregularly-shaped particles with PEG-4000and oleic acid as the templates.According to these changes of product phase and morphology, the influences ofthe templates were analyzed to propose possible growth mechanisms in differentconditions.The as-obtained Sm₂O₃particles with different morphologies werecharacterized by UV-vis absorption spectra to calculate their corresponding bandgaps. The results show that the obtained products under hydrothermal conditionscould have high absorption in ultraviolet range of200—250nm, where thehighest peak were found at230nm. Besides, a weak absorption peak could alsobe found at410nm to suggest possible optical properties in visible-light range.The products prepared under solvothermal conditions exhibit high ultravioletabsorption peaks at the range from200to280nm with the highest peaks at230—250nm. Moreover, another weak visible light absorption peak could be foundat410nm. The corresponding band gaps of these hydro/solvothermal-treatedparticles present various value from4.820eV to4.928eV, which is suggested tobe related with their different sizes and microstructures. These differences arebelieved to results in the change of quantum size effect and microscopic stress ofthe products to show different optical properties.更多还原