Bi2Te3的水热合成及其高温高压烧结

以Bi(NO3)3和Te粉为原料,水合肼为还原剂,采用水热法保温24h,分别在150℃和180℃制备了Bi2Te3纳米粉末。通过X射线衍射、透射电镜、扫描电镜等分析方法对产物的物相组成和微观形貌进行了表征。实验结果表明,水热法可以制备出纯相纳米级别的Bi2Te3粉末,并且晶粒尺寸随着反应温度升高有增大的趋势。最后采用高温高压法对纳米Bi2Te3粉末进行烧结,分析了烧结温度和压力对样品室温热电性能的影响。结果显示,在0.94GPa、753K条件下烧结后样品的室温功率因子达到16μW/(cm.K2)。     

低温湿化学还原法制备Bi2Te3单晶纳米棒

采用低温湿化学还原法,以Bi(NO3)3·5H2O和TeO2为原料,通过乙二胺四乙酸(EDTA)参与调节使反应体系为中性,以NaBH4为还原剂,以表面活性剂Brij56(HO(CH2CH2O)10C16H33)为晶体生长调控剂,制备了Bi2Te3纳米棒.通过X射线衍射(XRD)、X射线荧光探针(XRF),扫描电镜(SEM)、透射电镜(TEM)和高分辨透射电镜(HRTEM)对样品的组成和结构进行了分析,同时初步探讨了Bi2Te3纳米棒的生长机理.结果表明,制备的Bi2We3纳米棒直径在30nm左右,长度在400nm左右,具有单晶结构;反应温度和Brij56的浓度对晶体形貌有较大的影响.     

单相Bi0.95Eu0.05Fe0.95Co0.05O3纳米颗粒的结构及其铁磁特性

采用溶胶-凝胶法制备了单相Bi0.95 Eu0.05Fe0.95 Co0.05 O3纳米粉末。用X射线衍射仪(XRD)和扫描电子显微镜(SEM)测量分析了其结构和形貌,结果表明样品仍为钙钛矿菱方结构。样品Fe2p的X射线吸收谱(XAS)表明样品中Fe的价态处于Fe2+和Fe3+的混合态。利用振动样品磁强计(VSM)测量样品的磁性特征,结果表明样品具有完整闭合的磁滞回线,表现出室温的铁磁性,相比BiFeO3样品磁性得到明显增强。     

纳米Y2O2S∶Tb X射线发光粉的合成及发光性质

以EDTA为螯合剂、尿素为沉淀剂,采用络合沉淀法制备了Y2O2S:Tb纳米X射线发光粉.通过X射线衍射(XRD)、光致发光(PL)光谱和X射线激发发光(XEL)光谱对纳米发光粉进行了表征,并研究了纳米晶的发光性能及Tb3+离子的能量传递过程.研究表明:所制备样品显示了单一的六角结构,其一次粒径约为32nm.在254nm紫外光和X射线激发下,Y2O2S:Tb X射线发光粉都显示了Tb3+离子的特征发射峰,分别起源于5D3和5D4能级到基态能级的跃迁.     

含水量对Bi2Te3纳米片合成的影响

本文采用溶剂热法制备热电纳米材料Bi2Te3,研究了不同含水量对所得产物组成与形貌的影响。利用X射线衍射(XRD)、能谱仪(EDS)、冷场发射扫描电子显微镜(FESEM)和透射电子显微镜(TEM)等对产物进行了详细表征分析。结果表明,反应体系无水,也可以获得标准的六角形Bi2Te3纳米片。随着含水量增加,产物出现团聚现象;含水量大于一定值时,开始出现Te和Bi2TeO5杂相。     

双元共掺杂Bi1-xLax(Fe0.95Mn0.05)O3多铁性材料的磁性研究

采用溶胶-凝胶法制备了Bi1-xLax(Fe0.95Mn0.05)O3(x=0,0.10,0.15)多晶样品。X射线衍射实验表明La、Mn离子共掺杂没有改变样品的四方晶格结构。X射线能量色散分析显示样品的化学组分几乎不变。Mn离子掺杂或者是(La、Mn)离子共掺杂,导致铁酸铋材料的磁性增强。X射线吸收精细结构实验表明Mn3+的局域结构的改变是样品磁性增强的原因。     

Co3O4纳米颗粒的制备及表征

以脱脂棉为碳源,硝酸钴为前驱物,采用碳辅助法焙烧制备了粒径为50nm Co3O4纳米颗粒。用X射线衍射(XRD)对不同焙烧温度(200~600℃)下样品的物相、晶粒度进行了研究,并结合傅立叶红外光谱(FT-IR)对Co3O4物相演变进行了分析,确定中间产物前躯体是CoCO3;通过扫描电镜(SEM)和透射电镜(TEM)对制备的Co3O4样品的形貌、粒径进行了分析;同时,X射线能谱(EDS)和氮气吸附-脱附曲线测试等表明制备的Co3O4表面存在碳元素和孔结构,具有较大的比表面积,有利于提升其光解水制氢能力。     

一维Bi2Te3基纳米材料的制备、结构控制与热电性能

热电材料的低维化可以改善材料电输运与热传输的矛盾,特别是一维纳米热电材料明显的晶体各向异性和强烈的量子禁闭效应,可大幅度提高材料的热电优值和热电转换效率。Bi2Te3是制造低温热电材料的最常用材料,在温差发电和半导体制冷方面具有广阔的商业应用前景。以一维Bi2Te3基纳米热电材料的制备技术为评述线索,重点论述一维Bi2Te3基纳米热电材料形貌参数(包括直径、长径比)、晶面取向等微观结构的调控方法、生长机理以及显微结构对热电性能的影响规律。指出发展新的一维Bi2Te3基纳米热电材料结构控制方法,研究一维纳米热电材料的定向排布及组装技术,从更深层次揭示一维结构与热电性能的关系,以及开发一维Bi2Te3基纳米热电材料在各领域的实际应用是未来研究的发展方向。     

多铁性材料Bi_(0.95)R_(0.05)(Fe_(0.95)Co_(0.05))O_3(R=La,Eu,Ho)的磁性及XAFS研究

利用溶胶-凝胶法成功制备双元素共掺杂Bi0.95R0.05(Fe0.95Co0.05)O3(R=La,Eu,Ho)系列样品。X射线衍射实验数据表明:Eu离子掺杂使得BiFeO3材料的晶体结构发生了变化。振动样品磁强计测量的样品磁性数据显示:La、Eu、Ho离子分别与Co离子共掺杂,能够提高样品铁磁性,而且Bi0.95Eu0.05(Fe0.95Co0.05)O3样品的铁磁性行为最明显。同步辐射X射线吸收精细结构实验结果说明:Eu离子掺杂改变了Fe原子的局域结构,使得Fe-O键长增加,影响了Fe3+-O-Co3+双交换作用,进而引起样品磁性的增强。     

水热合成Ag离子改性修饰Bi_2WO_6及其光催化性能

通过水热法以固体AgNO3为Ag离子来源,成功制备出系列Ag离子改性修饰Bi2WO6复合光催化剂,并采用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、X射线光电子能谱仪(XPS)、能谱仪(EDS)和紫外-可见漫反射光谱(DRS)技术对其进行分析表征。研究表明,Ag离子可能取代Bi2WO6中的Bi 3+离子进入晶格,从而调节了禁带宽度。另一方面,纯Bi2WO6与Ag离子改性修饰Bi2WO6样品均为由纳米片自组装而成的球形结构,直径约为2~6μm。与纯Bi2WO6相比,Ag离子改性修饰Bi2WO6样品的结晶度较高且纳米片的排列也更致密,其光催化活性明显提高。在本文中形貌和能隙的优化是光催化性能提升的主要原因。当AgNO3的投加量为10%(摩尔分数)时,罗丹明B的降解率提高了近42%。     

Synthesis of single crystal Bi2Te3 nanoplates via an inorganic-surfactant-assisted solvothermal route

Single crystal Bi₂Te₃ nanoplates have been successfully obtained by a solvothermal method adopting a lamellar structure as the precursor. Various techniques such as X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) have been used to characterize the obtained products. The results show that the as-synthesized samples are rhombohedral-structured Bi₂Te₃ single-crystal nanoplates, whose growth direction is perpendicular to c-axis. In addition, some important experiment parameters such as the water/ethanol volume ratio and pH value have been discussed.     

Structural, electrical and optical properties of Bi2Se3 and Bi2Se(3−x)Tex thin films

Thin films of Bi₂Se₃, Bi₂Se_2.9Te_0.1, Bi₂Se_2.7Te_0.3 and Bi₂Se_2.6Te_0.4 are prepared by compound evaporation. Micro structural, optical and electrical measurements are carried out on these films. X-ray diffraction pattern indicates that the as-prepared films are polycrystalline in nature with exact matching of standard pattern. The composition and morphology are determined using energy dispersive X-ray analysis and scanning electron microscopy (SEM). The optical band gap, which is direct allowed, is 0.67 eV for Bi₂Se₃ thin films and the activation energy is 53 meV. Tellurium doped thin films also show strong optical absorption corresponding to a band gap of 0.70-0.78 eV. Absolute value of electrical conductivity in the case of tellurium doped thin film shows a decreasing trend with respect to parent structure.     

A facile hydrothermal route to spinel CoCo2O4 nanotubes and porous nanostructures without assisted surfactants and templates

Spinel CoCo₂O₄ nanotubes and porous nanostructures have been synthesized by a novel hydrothermal method from Co(NO₃)₂·6H₂O in mixtures of ammonia and cyclohexane at 220 °C. The morphology and phase of CoCo₂O₄ can be controlled by adjusting the experimental parameters that include the Co²⁺ concentration and the volume ratio of ammonia to cyclohexane. X-ray diffraction and transmission electron microscopy analyses were used to characterize the products. The formation mechanisms of CoCo₂O₄ nanostructures is proposed in detail. The electrochemical properties of the as-prepared samples have been investigated.     

Microstructural features and deformation-induced lattice defects in hot-extruded Bi2Te3 thermoelectric compound

Bismuth telluride (Bi₂Te₃) bulk material was prepared by a powder hot-extrusion technique. The microstructure, texture evolution, and deformation-induced lattice defects, as well as the effect of heat treatment on its microstructure and thermoelectric properties were investigated. As-extruded Bi₂Te₃ compound was found to be characterized by a dynamically and statically recrystallized microstructure with fine-equiaxed grains and low dislocation density. The majority of boundaries in the extruded specimens were large-angle boundaries with average misorientation angles of more than 30°. There was no significant change in dislocation configuration, even after heat treatment at a temperature higher than the extrusion temperature. Moreover, the Seebeck coefficient and electrical resistivity of the extruded specimens could not be improved by annealing. Microstructural examinations indicated the existence of a deformation-induced stacking disorder with local atomic shift, which we term “phase disorder,” on the basal plane in the extruded Bi₂Te₃ compound. The presence of this structural defect may be one of the main reasons for the slightly lower values of thermoelectric properties for the hot-extruded Bi₂Te₃ compound, compared with a unidirectionally solidified specimen.     

Synthesis of (Hg,X)Ba2Ca2Cu3Ox Superconductors

Synthesis and processing parameters for (Hg_1–xBi_x)Ba₂Ca₂Cu_3.1O_y were optimized for growth at temperatures suitable for growth on Ag and Au substrates (<850° C). Use of Bi₂CuO₄ as a Bi source combined with variations of BaCaCuO precursor phase assemblages allowed the formation of some liquid phase during the reaction and resulted in dense (Hg_1–xBi_x)Ba₂Ca₂Cu_3.1O_y samples with aligned colonies of grains. Magnetization measurements in fields up to 30 T indicated good intergrain coupling within the large grain colonies. The results of the Bi doped samples are compared with those of previously reported Re doped samples.     

Te纳米线模板法加工Bi_2Te_3-Te片式棒热电材料(英文)

以碲纳米线为模板,采用简便的回流法大规模合成了Bi2Te3-Te片式棒一维材料,产量达到90%.利用X射线衍射、扫描电镜、X射线能谱、透射电镜对样品进行了分析.系统的研究了KOH、EDTA以及反应时间对产物结构的影响,提出了这种异质结构的形成机制.本制备方法可以推广到合成其它金属和半导体的一维特殊纳米结构.     

Structural,optical, and magnetic properties of polycrystalline Co-doped TiO2 synthesized by solid-state method

We have used a solid-state method to synthesize polycrystalline Co-doped TiO₂ diluted magnetic semiconductors (DMSs) with Co concentrations of 0, and 0.5 at.%. X-ray diffraction patterns reveal that Co doped TiO₂ crystallizes in the rutile tetragonal structure with no additional peaks. Transmission electron microscopy (TEM) did not indicate the presence of magnetic parasitic phases and confirmed that Co ions are uniformly distributed inside the samples. Optical absorbance measurements showed an energy band gap which decreases after doping with the Co atoms into the TiO₂ matrix. Magnetization measurements revealed a paramagnetic behavior for the as-prepared Co-doped TiO₂ and a ferromagnetic behavior for the same samples after annealed under a mixture of H₂/N₂ atmosphere.     

Photocatalytic degradation of RhB over MgFe2O4/TiO2 composite materials

MgFe₂O₄/TiO₂ (MFO/TiO₂) composite photocatalysts were successfully synthesized using a mixing-annealing method. The synthesized composites exhibited significantly higher photocatalytic activity than a naked semiconductor in the photodegradation of Rhodamine B. Under UV and visible light irradiation, the optimal percentages of doped MgFe₂O₄ (MFO) were 2 wt.% and 3 wt.%, respectively. The effects of calcination temperature on photocatalytic activity were also investigated. The origin of the high level of activity was discussed based on the results of X-ray diffraction, UV-vis diffuse reflection spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen physical adsorption. The enhanced activity of the catalysts was mainly attributed to the synergetic effect between the two semiconductors, the band potential of which matched suitably.     

Hydrothermal synthesis of single-crystalline Bi2Te3 nanoplates

Novel Bi₂Te₃ nanoplates with about 0.2-1 μm in diagonal and 100 nm in thickness have been facilely synthesized via hydrothermal routes in the presence of polyvinylpyrrolidone (PVP). Various techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier transform infrared spectrometry (FT-IR) have been used to characterize the obtained products. The results show that the existence of PVP is vital to the formation of the plate-like morphology. Other factors, such as the reaction temperature and the different surfactants also have influence on the morphology of the final products to some extent.     

Ferroelectric Bi3.25La0.75Ti3O12 thin films on a conductive Sr4Ru2O9 electrode obtained by pulsed laser deposition

Strontium ruthenate and Bi_3.25La_0.75Ti₃O₁₂ (BLT) layers were grown on Si(100) substrate using pulsed laser deposition technique. Starting from a Sr₂RuO₄ target, we obtained single phase films composed of Sr₄Ru₂O₉; on these strontium ruthenate electrodes, textured and non-textured BLT were grown at 700 °C. Structural characterizations of these double layers were done by X-ray diffraction, scanning electron microscopy, normal and high-resolution transmission electron microscopy. The Van der Pauw's resistivity measurements indicate that Sr₄Ru₂O₉ can be used as a back electrode. The temperature dependence of the resistivity at low temperatures is , which corresponds to a variable-range hopping mechanism.