Synthesis and thermoelectric properties of Mn-doped AgSbTe2 compounds

Polycrystalline p-type Ag 0.9 Sb 1.1 x Mn x Te 2.05（x = 0.05,0.10,and 0.20） compounds have been prepared by a combined process of melt-quenching and spark plasma sintering.The sample composition of Ag 0.9 Sb 1.1 x Mn x Te 2.05 has been specially designed in order to achieve the doping effect by replacing part of Sb with Mn and to present the uniformly dispersed Ag 2 Te phase in the matrix by adding insufficient Te,which is beneficial for optimizing the electrical transport properties and enhancing the phonon scattering effect.All the samples have the NaCl-type structure according to our X-ray powder diffraction analysis.After the treatment of spark plasma sintering,only the sample with x = 0.20 has a small amount of MnTe 2 impurities.The thermal analysis indicates that a tiny amount of Ag 2 Te phase exists in all these samples.The presence of the MnTe 2 impurity with high resistance and high thermal conductivity leads to the deteriorative thermoelectric performance of the sample with x = 0.20 due to the decreased electrical transport properties and the increased thermal conductivity.In contrast,the sample with x = 0.10 exhibits enhanced thermoeletric properties due to the Mn-doping effect.A dimensionless thermoelectric figure of merit of 1.2 is attained for the sample with x = 0.10 at 573 K,showing promising thermoelectric properties in the medium temperature range.     

The crystal structures and physical properties of the solid solution compound Ba5Y8-xMn4021-1.5x （x = 0, 1）

New oxometallides with the formula Ba5Y8-xMn4021-1.5x （x = 0, 1） are prepared through an atmosphere-controlled solid-state reaction. Two single-phase samples with Ba/Y/Mn atomic ratios 5/8/4 （Y8） and 5/7/4 （Y7） are obtained. The crystal structures and the physical properties of the compounds are investigated by X-ray powder diffraction, magnetization, conductivity, and dielectricity measurements. The Ba5Y8-xMn4021-1.5x compound is demonstrated to be a Y-deficient solid solution. The solid solution compound Ba5Y8-xMn4021-1.5x crystallizes into tetragonal symmetry with the space group I4/m. Detailed structure analysis by Rietveld refinement of the X-ray powder diffraction data reveals that the Y vacancies occur preferentially at the Y（2） site. Thermal magnetization measurements indicate the presence of antiferromagnetic interaction between Mn ions in the compounds, and temperature-dependent resistivity measurements show that insulator-semiconductor transitions occur around 175 K and 170 K for the Y8 and Y7 samples, respectively. Strong frequency dependences of the dielectric constant are observed above -175 K for the two compounds.     

镁颗粒群非稳态着火过程数值模拟

建立了镁颗粒群着火的一维非稳态有限影响体模型, 数值模拟颗粒群中镁颗粒的着火过程. 研究表明, 当镁颗粒表面反应加剧之后,颗粒相温度急剧上升, 迅速达到着火, 而其周围气相的温升速率却远小于颗粒的温升速率; 在着火过程中气相温度只在颗粒表面附近升高比较明显, 整体温度升高不大. 分析了颗粒群内部参数和环境参数对镁颗粒群着火的影响. 随颗粒浓度的增加, 颗 粒群变得易于着火, 其着火时间变短, 但颗粒浓度增大到一定程度后, 继续增大该值将对颗粒群的着火起消极作用. 环境压力对颗粒群着火的影响比较小,在1-5 atm范围内颗粒群的着火性能基本不变. 气相中氧气浓度对颗粒群的着火性能影响也不显著, 但当氧气浓度过小时, 对着火过程的影响将大大增强.颗粒粒径、气相/颗粒相初温、辐射源温度对颗粒 群着火的影响巨大,小粒径、高温度促使颗粒群快速着火.数值模拟与文献中试验 结果的变化趋势相一致.     

空穴掺杂Sr2FeMoO6的晶体结构及磁性研究

采用传统高温固相反应法制备了空穴掺杂的系列样品Sr2xKxFeMoO6（0≤x≤0．04）,研究了其晶体结构和磁性质．X射线粉末衍射结果表明该系列样品均为单相,四方晶系,空间群为I4／m．碱金属K的含量可以调控反位缺陷的浓度．未掺杂样品Sr2FeM006在280K时的原胞磁矩为1．12μB．掺杂量为x=0．04样品的原胞磁矩为1．26μB．阳离子有序、晶格畸变是影响Sr2-xKxFeMoO6磁性的重要因素．     

JH荧光粉与502胶熏显加染法对铝合金客体上汗潜手印的研究

为提高铝合金客体上汗潜手印的显出率,通过实验对铝合金客体上的汗潜手印,分别采用JH荧光粉末显现和502胶熏显荧光试剂染色两种方法进行研究,两种方法均能收到良好的效果。     

稀土氧化物粉末样品的光声光谱研究

利用光声光谱方法对几种常见的稀土氧化物粉末样品在紫外-可见、近红外, 以及中红外波段的光声光谱进行了测量与分析。根据光声光谱图和稀土离子的能级图, 对稀土离子的激发态电子的辐射和无辐射跃迁进行了探讨。与传统的透射谱和吸收谱相比较, 光声光谱具有分辨率高、快速、无损检测等优点, 特别适合于研究不透明、高反射和高散射粉末样品的光学性质。     

考虑接触热阻的纳米颗粒堆积热导率的分析

本文首先使用Callaway热导率模型对SiO₂纳米颗粒的热导率进行了近似计算,然后耦合堆积纳米孔隙内的导热和辐射、颗粒接触热阻,基于颗粒堆积单元结构模型的一维传热分析,最终推导得到了颗粒堆积有效热导率关于颗粒直径和温度、堆积孔隙率、颗粒热导率、气相热导率、辐射传热和接触热阻的关系式,并用该式进行了相关讨论。研究结果表明,对于纳米颗粒堆积,界面接触热阻不容忽略;在低孔隙率和颗粒不参与辐射的条件下,由于受到接触热阻的影响,存在最佳孔隙率（或密度）使得堆积热导率存在最大值。     

超细La2O3纳米粉末制备过程的电子显微镜动态观察

用超高压透射电子显微镜原位加热动态观察的方法研究从非晶氢氧化镧转变为纳米级氧化镧超细粉过程中显微组织和结构的变化。电子衍射花样证实在试样被加热到４００℃以上时转变为氧化镧纳米粉，其颗粒尺寸为２０￣５０ｎｍ。     

SBP挤压成型工艺的应用

增塑粉末挤压成型技术是一项十分关键的新成型技术，其关键的工艺步骤包括：增塑剂的选择与配方，粉末与增塑剂的混合，喂料挤压成型，挤压毛坯的脱脂与烧结，其核心技术是增塑剂的设计。本研究以SBP为增塑剂，研究了增塑剂的含量对挤压毛坯密度的影响，研究了SBP脱脂机理，通过常规真空烧结获得的YG6硬质合金产品性能与CIP成型的产品性能相当。