Vacancy Manipulation Induced Optimal Carrier Concentration,Band Convergence and Low Lattice Thermal Conductivity in Nano-Crystalline SnTe Yielding Superior Thermoelectric Performance

Synergetic optimization of electrical and thermal transport properties is achieved for SnTe-based nano-crystalline materials. Gd doping is able to suppress the Sn vacancy, which is confirmed by positron annihilation measurements and corresponding theoretical calculations. Hence, the optimal hole carrier concentration is obtained, leading to the improvement of electrical transport performance and simultaneous decrease of electronic thermal conductivity. In addition, the incremental density of states effective mass m* in SnTe is realized by the promotion of the band convergence via Gd doping, which is further confirmed by the band structure calculation. Hence, the enhancement of the Seebeck coefficient is also achieved, leading to a high power factor of 2922 µW m⁻¹ K⁻² for Sn_0.96Gd_0.04Te at 900 K. Meanwhile, substantial suppression of the lattice thermal conductivity is observed in Gd-doped SnTe, which is originated from enhanced phonon scattering by multiple processes including mass and strain fluctuations due to the Gd doping, scattering of grain boundaries, nano-pores, and secondary phases induced by Gd doping. With the decreased phonon mean free path and reduced average phonon group velocity, a rather low lattice thermal conductivity is achieved. As a result, the synergetic optimization of the electric and thermal transport properties contributes to a rather high ZT value of ≈1.5 at 900 K, leading to the superior thermoelectric performance of SnTe-based nanoscale polycrystalline materials.     

机械力化学合成纳米晶体的研究

介绍了机械力化学的概念、作用机理及其表征技术。阐述了机械力化学制备纳米粉体的机理和优越性,并主要以BaTiO3纳米晶为例,研究其合成方法及反应机制。对其未来发展进行了展望。     

纤维素酶制备纳米纤维素晶体的研究

采用超声渡预处理棉纤维,用纤雏素酶制备纳米纤维素晶体(NCC).研究了反应方式、反应时间、反应温度、酶用量等对酶解反应的影响,确定了最佳酶解条件:酶液与底物比为8(mL:g),pH值为4.8,酶解温度为45℃,酶解时间为2 d.在此条件下制备的NCC单分散性比较好.     

基片温度对纳米金刚石薄膜掺硼的影响

采用微波等离子体化学气相沉积法,以氢气稀释的乙硼烷为硼源进行了纳米金刚石(NCD)薄膜的生长过程掺硼,研究了基片温度对掺硼NCD薄膜晶粒尺寸、表面粗糙度、表面电阻和硼原子浓度的影响.利用扫描电子显微镜和原子力显微镜观察NCD薄膜的表面形貌,并通过Imager软件对原子力显微镜数据进行分析获得薄膜的表面粗糙度及平均晶粒尺寸信息;采用四探针测量掺硼NCD薄膜的表面方块电阻,利用二次离子质谱仪对掺杂后NCD薄膜表面区域的硼原子浓度进行测量.实验结果表明,较高的基片温度有利于提高薄膜的导电能力,但随着基片温度的提高,NCD薄膜的平均晶粒尺寸和表面粗糙度逐渐增大;此外,当反应气体中的乙硼烷浓度一定时,掺杂后NCD薄膜的表面硼原子浓度随基片温度升高存在一个饱和值.在所选乙硼烷浓度为0.01%的条件下,基片温度在700℃左右可以在保证薄膜表面电性能的基础上保持较好的表面形貌.     

PZT纳米晶的改进型溶胶-凝胶法制备及其生长过程研究

以乙二醇为溶剂,硝酸锆为锆源,采用改进的溶胶-凝胶法,通过优化工艺参数制备了纳米Pb(Zr0.52Ti0.48)O3(PZT).通过对工艺条件研究, 揭示了体系的凝胶化可通过升高温度和增加pH值来实现.通过对溶胶的红外光谱分析给出了溶胶、凝胶形成的机理.通过TG-DTA、XRD、SEM、TEM等手段对从凝胶到PZT纳米晶的生长过程及性能进行了表征.实验证明,改进后工艺简单易行,溶胶稳定,干凝胶在650℃热处理2h,获得较完整的钙钛矿型PZT,粒径约为50～100nm.     

纳米晶复合涂层应用于火星玻璃盖片防尘的探索

目的制备超微结构的纳米晶复合涂层,降低火星环境中灰尘颗粒在玻璃表面的粘附,并通过翻转操作,最大限度地清除沉积的灰尘,恢复太阳能电池的发电能力。方法采用水热法和表面修饰,制备了纳米晶复合防尘涂层。通过电子显微镜、分光光度计、接触角仪和翻转除尘试验分别对涂层的微观结构、可见-近红外光透过率、表面性质和除尘效率进行了分析。结果由直径大约为27nm的ZnO纳米棒构成的独特涂层结构,使灰尘颗粒与涂层表面的接触面积相比于普通玻璃减小了一个数量级,可见光区的透过率提高了1.1%,近红外区透过率提高了0.4%。用氟化物进行表面修饰后,涂层的水接触角由25°～45°升高至155°～165°。经90°缓慢翻转,纳米晶复合涂层对50～100μm和30～50μm灰尘颗粒的清除效率分别为80%～90%和60%～70%;而在相同测试条件下,普通玻璃的防尘效率仅为37.5%和6.3%。由翻转后涂层表面灰尘的分布情况和倾斜表面上单颗粒的受力分析发现,灰尘颗粒的脱落存在滑落和滚落两种模式,高位落下的颗粒将部分动能传递给低位静止的颗粒,促使更多静止颗粒的滑落或滚落,形成"雪崩"状的特殊形貌。结论 ZnO纳米晶复合涂层不仅可以提高可见光和近红外光的透过率,还可以极大地减小与灰尘颗粒的接触面积,降低颗粒的粘附力,在不使用高压电能的情况下,经过翻转操作,清除效率可达80%以上,这将为火星上灰尘的清除提供一种安全的方式。     

纳米金刚石薄膜的光学性能研究

用热丝化学气相(HFCVD)法在硅衬底上制备了表面光滑、晶粒致密均匀的纳米金刚石薄膜,用扫描电镜(SEM)和原子力显微镜(AFM)观测薄膜的表面形貌和粗糙度,拉曼光谱表征膜层结构,紫外-可见光分光光度计测量其光透过率,并用椭圆偏振仪测试、建模、拟合获得了表征薄膜光学性质的n,k值.结果表明薄膜的晶粒尺寸在100nm以下,表面粗糙度仅为21nm;厚度为3.26(m薄膜在632.8nm波长处的透过率为25%,1100nm波长处达到50%.采用直接光跃迁机制估算得到纳米金刚石薄膜的光学能隙(Eg)为4.3 eV.     

软磁铁氧体材料的发展趋势及产业化研究和开发的几个误区

纳米结构的金属软磁材料的崛起，使高频性能优良的铁氧体软磁材料面临着巨大的挑战。本文在对软磁材料，特别是软磁铁氧体材料的发展过程及发展趋势进行综合分析之后，指出了一些当前在软磁材料研究和开发中普遍容易忽视的问题。     

Fabrication of nano-crystalline W-Ni-Fe alloy with Mo and rare earth element additives

Three kinds of nano-crystalline high density alloys (86W-7Ni-3Fe-4Mo, 90W-4Ni-2Fe-4Mo and 90W4Ni-2Fe-3.8Mo-0.2RE) were fabricated by a technique combining lower temperature vacuum sintering with highenergy ball milling mechanical alloying. The crystalline size and microstructures of the specimens sintered at different sintering temperatures were examined by X-ray diffraction(XRD) and scanning electron microscope(SEM). The results show that the optimal sintering temperature of 86W-7Ni-3Fe-4Mo, 90W-4Ni-2Fe-4Mo and 90W-4Ni-2Fe-3.8Mo-0.2RE alloys are 1 300 - 1 350℃. When they are sintered at 1 300℃ for 75 min， the hardness of three kinds of specimens can reach above HRC30, the relative density can reach above 96%, and 90W-4Ni-2Fe-3.8Mo-0.2RE alloy possesses the best integrated properties, its hardness is HRC35 and its relative density is 98%.     

电沉积纳米镍-钻合金在金刚石工具制备中的应用研究

采用纳米镍一钴镀层制备电镀金刚石工具以期提高工具的性能。通过考察脉冲参数、细化添加剂、硫酸钴对镀层显微硬度的影响,得出结论：细化添加剂、硫酸钴都能细化晶粒,两者有竞争关系;改变峰值电流密度和开通时间可以细化晶粒,脉冲周期过短会造成晶粒粗化。镀层中钴的质量分数为9％,表面较光整,平均晶粒尺寸在14nm左右,显微硬度达到609HV。确定了制造金刚石工具最佳的电镀工艺参数,由其制得的工具平均寿命比纳米镍镀层材料工具高16％。