水热合成Sb_2Se_3纳米线及其对Bi_2Te_3纳米粉末热电性能的影响

以SbCl3和Se粉为原料,水合肼(N2H4·H2O)为还原剂,采用水热法在150℃下,分别保温不同的时间合成Sb2Se3纳米粉末.通过X射线衍射(XRD)、场发射电子扫描电镜(FESEM)、透射电镜(TEM)以及高分辨透射电镜(HRTEM)等分析方法对产物的物相成分和微观形貌等进行了表征,实验结果表明保温时间达到24h时,获得产物为单相Sb2Se3纳米线晶体.根据实验结果还研究了水热合成Sb2Se3纳米线晶体可能的反应及生长机理,结果表明一维纳米线沿[001]方向生长,纳米线的形成与其独特的层状晶体结构有关.最后采用放电等离子体快速热压烧结法将水热合成的Bi2Te3纳米粉末与不同含量Sb2Se3纳米线进行复合,分析了Sb2Se3纳米线对Bi2Te3纳米材料热电性能的影响,发现复合约1at%Sb2Se3纳米线可以使Bi2Te3纳米材料热电性能有一定提高.     

微结构对Bi_2Sr_2Co_2O_y化合物电性能的影响

通过溶胶-凝胶法制备单相Bi2Sr2Co2Oy化合物,通过添加PEG20000和超声分散对化合物粉体微结构进行调控,采用SPS烧结得到了致密的块体.探索了微结构对Bi2Sr2Co2Oy化合物电性能的影响规律.结果表明,添加PEG20000和超声分散可以明显降低Bi2Sr2Co2Oy化合物粉体的晶粒尺寸,使烧结块体的晶粒尺寸大幅度减小,从而显著提高材料的电性能.温度为873K时,添加PEG20000并超声处理所制备样品烧结块体获得了最高ZT值0.041.     

共沉淀法合成近零膨胀ZrW2O8/ZrO2复合陶瓷的致密化

采用化学共沉淀法合成前驱体,经1150℃ 烧结3.5 h得到近零膨胀26 wt% ZrW₂O₈/ZrO₂复合陶瓷,并利用X射线衍射仪、扫描电镜和热膨胀仪研究了原料中加入Al(NO₃)₃·9H₂O对26 wt% ZrW₂O₈/ZrO₂复合陶瓷的相组成、致密度和热膨胀性能的影响。研究结果表明,少量添加Al(NO₃)₃·9H₂O可有效提高复合材料致密度,所得复合陶瓷的组分仍为立方结构的α-ZrW₂O₈和单斜的m-ZrO₂,其中添加2.21 wt% Al(NO₃)₃·9H₂O的复合材料的致密度达到理论密度的98.67%,且对复合陶瓷的热膨胀性能影响不大。其促进致密化机制为晶界处低熔点液相物质Al₂(WO₄)₃提高了复合材料的烧结性能,消除气孔促进致密化。     

In掺杂β-Zn_4Sb_3热电材料的制备与电热输运

设计了一系列名义组成为Zn4Sb3-xInx(0~0.08,Δx=0.02)的In掺杂β-Zn4Sb3基块体材料,并用真空熔融-随炉冷却-放电等离子体烧结工艺成功制备出无裂纹的In掺杂单相β-Zn4Sb3基块体材料.300~700K内材料的电热输运特性表明,In杂质对Zn4Sb3化合物的Sb位掺杂可导致载流子浓度和电导率大幅度增大、高温下本征激发几乎消失和晶格热导率显著降低,x=0.04和0.08的Zn4Sb3-xInx的In掺杂β-Zn4Sb3化合物700K时晶格热导率均仅为0.21W/(m·K).与纯β-Zn4Sb3块体材料相比,所有In掺杂β-Zn4Sb3基块体材料的ZT值均显著增大,x=0.06的Zn4Sb3-xInx的In掺杂β-Zn4Sb3基块体材料700K时ZT值达到1.13,提高了69%.     

超临界流体干燥法制备TiO2/ Fe2O3 和TiO2/ Fe2O3/ SiO2 复合纳米粒子及光催化性能

以TiCl₄ 、Fe (NO₃ )₃·9H₂O 和Na₂SiO₃19H₂O 为原料, 采用溶胶凝胶法结合超临界流体干燥法(SCFD)制备了纳米级TiO₂/ Fe₂O₃ 和TiO₂/ Fe₂O₃/ SiO₂ 复合光催化剂。以光催化降解苯酚对所得催化剂的催化活性进行了评价。结果表明, 纳米TiO₂/ Fe₂O₃ 复合粒子与单组分TiO₂ 比较, 复合粒子光催化活性高于单组分的TiO₂, 6h 苯酚降解率高达95.9 %。SiO₂ 的加入可以抑制纳米粒子粒径的长大和晶相的转变, 增强TiO₂ 纳米粒子的热稳定性。复合光催化剂中Fe₂O₃ 最佳掺入量为0.06 %, SiO₂ 最佳掺入量为10 %(摩尔分数) 。并用XRD、TEM 和FTIR 等手段进行了表征。TiO₂ 以锐钛矿型形式存在, SiO₂ 以无定性形式存在。比较了不同制备方法制得的TiO₂/ Fe₂O₃ 复合光催化剂, 得出超临界干燥法制备的光催化剂具有粒径小、比表面积大、分散性好、光催化活性高等特点。采用超临界流体干燥可直接得锐钛型纳米复合光催化剂。     

AgSbTe_2热电化合物的机械合金化制备

以Ag、Sb、Te单质粉体为原料,采用机械合金化工艺制备了单相的AgSbTe2化合物粉体。系统研究了机械合金化工艺制度,包括球料比、转速、球磨时间对粉体相组成、颗粒尺寸的影响。结果表明,在球料比为20∶1、转速大于400rpm、球磨时间大于15h时,可得到单相AgSbTe2化合物粉体;当球料比为20∶1、转速为600rpm、球磨48h后,可得到平均粒径约370nm单相AgSbTe2化合物粉体,其表面小颗粒尺寸约为50～100nm。     

超声化学法合成聚苯胺及其表征

采用超声化学法,在没有任何模版的条件下合成了产物纯净、尺寸单一的纳米棒状聚苯胺,采用SEM、XRD、TG和BET等方法对产物进行了表征.研究表明,氧化剂过硫酸铵的用量与产率存在较大关联,氧化剂和苯胺单体的物质的量比1∶1时可以达到最大产率;盐酸浓度对产物形貌有较大影响,只有盐酸浓度达到一定程度才可以得到纳米棒状聚苯胺;超声化学法合成的聚苯胺比表面积要大大高于市售和机械搅拌法合成的聚苯胺,比表面积可达29.5m~2/g.     

TiO2-SiO2复合材料的结构调变对其催化应用的影响

TiO₂-SiO₂复合材料(TSCM)的催化应用性能受到其所含TiO₂物种的晶相和SiO₂骨架的孔道结构的显著影响。本文归纳总结了TSCM中TiO₂物种晶相、SiO₂骨架的孔道结构、形貌等特性的调变规律及其对TSCM催化性能的影响,并展望了TSCM材料的结构特性演变趋势以及在制备方法上的取舍。TSCM直接作为催化剂时,其活性位普遍被认为是TiO₂-SiO₂界面上的Ti—O—Si键位和酸性位点。而作为载体材料时,TSCM中的TiO₂物种可以与负载的金属活性中心表现出显著的载体-金属相互作用(SMSI),TiO₂物种的晶相可以对形成的金属活性中心的性能产生显著影响。在TSCM材料的合成研究中,合成含有单一锐钛矿相(Anatase)TiO₂物种的Anatase-SiO₂或单一金红石晶相(Rutile)的Rutile-SiO₂类型TSCM材料,以及同时含有这两个晶相TiO₂,但晶相比例可调的A/R-SiO₂类型TSCM材料仍充满挑战。TSCM的SiO₂骨架特性调控也同样具有挑战,如何在得到特定晶相和粒子尺寸的TiO₂物种的同时获得特定孔道特性和形貌特征的SiO₂骨架,仍是研究的难点和热点。两步法无需同时控制TiO₂和SiO₂物种的制备参数,重现性好,多用于特殊形貌的TSCM的制备,但通常其中TiO₂物种的分散度不佳。而一步法制备过程简短,更容易得到多孔-大比表面积材料,有利于实现TiO₂粒子的尺寸控制及其在SiO₂骨架中的均匀分布,从而得到更丰富的Ti—O—Si界面活性物种,但需要在同一合成体系中同时控制相互影响的TiO₂和SiO₂物种的制备参数,调控难度极大,与两步法相比,重现性较差。     

ZrO2在β"─Al2O3复合陶瓷中的作用

本文研究了四方和立方ZrO₂在与Na-β"-Al₂O₃的复合陶瓷中作为第二相所起的各种作用。结果说明ZrO₂对复合陶瓷具有细化晶粒、改善显微结构、提高强度和断裂韧性的作用,与此同时也在一定程度上降低离子电导率。在提高力学性能方面,四方ZrO₂除了具有与立方ZrO₂相同的弥散颗粒的作用外,相变所起的作用也是很显着的。ZrO₂-Na-β"-Al₂O₃复合陶瓷是一种有应用价值的固体电解质材料。     

超声协同微球型Bi2O2CO3降解罗丹明B的研究

Bi_2O_2CO_3是一种Bi类半导体催化剂,文章研究了它的超声催化性能。首先,采用水热法制备了微球型的Bi_2O_2CO_3,利用X射线衍射(X-ray Diffraction, XRD)、扫描电子显微镜(Scanning Electron Microscope, SEM)、紫外-可见漫反射光谱对样品的晶体结构、微观形貌、光学特性进行了表征。然后,以罗丹明B(Rh B)作为模型污染物,通过研究超声催化降解罗丹明B来评测Bi_2O_2CO_3的超声催化性能。研究了催化剂的浓度(Ccatalytic)、初始罗丹明B染料的浓度(CRhB)和超声功率(P)等实验因素对超声催化降解效率的影响。得出在Ccatalytic=3 g·L-1,CRhB=10 mg·L-1和P=400 W条件下降解罗丹明B的效率最高,其最高降解效率可以达到91.7%。     

One-pot synthesis of intestine-like SnO2/TiO2 hollow nanostructures

In the present study the intestine-like binary SnO₂/TiO₂ hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO₂ spheres and Ti(SO₄)₂ are used as colloid seeds and Ti-source, respectively. The novel core (SnO₂ hollow sphere)-shell (TiO₂) nanostructures possess a large surface area of 122 m²/g (calcined at 350 °C) and a high exposure of TiO₂ surface. The structural change of TiO₂ shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO₂ could form even at room temperature due to the presence of SnO₂ core and the unique core-shell interaction.     

Synthesis, structure and exchange bias in Cr2O3/CrO2/Cr2O5 particles

We report on the synthesis, structure and magnetic properties of a novel exchange bias system with Cr₂O₃/CrO₂/Cr₂O₅ interfaces. Chromium oxide particles with mixed chromium valences were prepared by sintering CrO₃ in air. X-ray diffraction patterns show that CrO₃ lost its oxygen gradually with increasing temperature and time through Cr₃O₈, Cr₂O₅, CrO₂, and finally Cr₂O₃ at temperatures above 760 K. X-ray photoelectron spectra indicate a low CrO₂ content and a binding energy of 579.3 eV for Cr 2p_3/2 photoelectrons in Cr₂O₅. Chromium dioxide was found to stably coexist with Cr₂O₃ and Cr₂O₅ in the particles. Magnetic measurements show hysteresis loop shifts in the sample, indicating an exchange bias induced by antiferromagnetic Cr₂O₃/Cr₂O₅ in ferromagnetic CrO₂. An exchange bias of 9 mT at 5 K and a coercivity of 26.3 mT were observed in the chromium oxide particles containing CrO₂.     

超声化学结合放电等离子烧结制备In4Se3化合物的热电性能研究

采用超声化学和后续还原热处理工艺合成了单相In4Se3化合物粉体,并结合放电等离子烧结技术(SPS)制备了致密的块体材料.对所得的块体材料的微结构和热电传输性能进行了系统研究.结果表明,块体样品的晶粒细小、排列紧密并存在显著的择优取向,同时样品中存在大量精细的层状结构,这使得块体样品的电热传输性能也表现出明显的各向异性.由于具有较高的Seebeck系数和较低的热导率,沿着SPS压力方向上样品表现出较好的热电性能,其最大ZT值在700 K可达到0.56,这与其它物理技术制备的In4Se3多晶材料的性能相当.     

Synthesis and properties of ZnFe2O4 replica with biological hierarchical structure

ZnFe₂O₄ replica with biological hierarchical structure was synthesized from Papilio paris by a sol–gel method followed by calcination. The crystallographic structure and morphology of the obtained samples were characterized by X-ray diffraction, field-emission scanning electron microscope, and transmittance electron microscope. The results showed that the hierarchical structures were retained in the ZFO replica of spinel structure. The magnetic behavior of such novel products was measured by a vibrating sample magnetometer. A superparamagnetism-like behavior was observed due to nanostructuration size effects. In addition, the ZFO replica with “quasi-honeycomb-like structure” showed a much higher specific capacitance of 279.4 F g⁻¹ at 10 mV s⁻¹ in comparison with ZFO powder of 137.3 F g⁻¹, attributing to the significantly increased surface area. These results demonstrated that ZFO replica is a promising candidate for novel magnetic devices and supercapacitors.     

Thermo-optic properties of TiO2, Ta2O5 and Al2O3 thin films for integrated optics on silicon

The direct measurement of the thermo-optic coefficients of aluminium oxide, tantalum pentoxide and titanium dioxide thin films is presented. Using ellipsometry on monolithically integrated permutations of the layers of silicon, silicon dioxide and the material under test, allows the direct measurement of the overall thermo-optic coefficient accounting for thermally induced changes in the dielectric permittivity and density of the materials as well as the elasto-optic effect due to the non-matching thermal expansion coefficients of the different materials.     

In-situ preparation of TiO2/SnO2 nanocrystalline sol for photocatalysis

A novel preparation method to synthesize TiO₂/SnO₂ nanocrystalline sol under mild conditions was presented. Ti(OC₄H₉)₄ used as a precursor was hydrolyzed in the rutile SnO₂ nanocrystalline sol, and in-situ formed TiO₂/SnO₂ nanocrystalline sol. The crystal structure, morphology and photocatalysis performance of samples were investigated. The results show that the additional rutile SnO₂ nano grains serve as heterogeneous crystal nucleus and exhibite the inducing effect on TiO₂ grains growth, thus leading to the changes in crystalline phase and particle morphology. In addition, the photoluminescence (PL) spectra analysis indicates that TiO₂/SnO₂ composite structure induces a better charge separation, and thus the photocatalytic activity of TiO₂/SnO₂ sol is increased significantly compared with TiO₂ sol.     

Synthesis of the intermetallic clathrate Na2Ba6Si46 by oxidation of Na2BaSi4 with HCl

A new preparation route to the intermetallic clathrate-I compound Na₂Ba₆Si₄₆ is introduced, which allows one to make large amounts of product with standard laboratory equipment. The precursor Na₂BaSi₄ is oxidized with gaseous HCl at 673 K to Na₂Ba₆Si₄₆, NaCl and BaCl₂. Full-profile refinement of the crystal structure from the X-ray powder diffraction data revealed a composition close to Na₂Ba₆Si₄₆ (Na_1.94(1)Ba_6.06(1)Si₄₆, space group , a=10.281(1) Å). Differential scanning calorimetry showed an exothermic effect at 874 K, indicating that Na₂Ba₆Si₄₆ is metastable. The product was additionally characterized by scanning electron microscopy. The electronic structure of Na₂Ba₆Si₄₆ was investigated by a first-principles, all-electron full-potential method, predicting metallic conductivity. Na₂Ba₆Si₄₆ obtained by oxidation with HCl shows Pauli paramagnetism; no bulk superconductivity was found down to 1.8 K in a magnetic field of 20 Oe.