超高性能的碳纳米管-橡胶复合材料的增强机理(英文)

合集下载

碳纳米管的特性及其高性能的复合材料综述

碳纳米管的特性及其高性能的复合材料综述摘要作为一种具有较强力学性能的材料，碳纳米管自诞生以来就受到了广泛关注，并且从以往的实践经验上来看，碳纳米管是非常理想的制备符合材料的形式。

在本文的研究当中，主要立足于这一领域进行分析，提出了碳纳米管本身所具备的特性，以及这种材料在实践过程当中的优越性，进而提出应用策略，希望能够在一定程度上起到借鉴作用。

关键词碳纳米管；复合材料；复合镀迄今为止，碳纳米管材料已经在诸多领域当中得以运用，并且取得了比较显著的成果，其中包括电极材料、符合材料、催化剂载体等诸多方面。

在应用过程当中，碳纳米管的优异性能能够使其在符合材料当中起到较强的作用。

本文研究的侧重点在于碳纳米管的制备和复合材料的应用方面，提出了碳纳米管的特性及其高性能的复合材料。

1 碳纳米管的结构及其性能从结构上来看，碳纳米管具有石墨层状的结构，其中包括单壁碳纳米管和多壁碳纳米管。

组成纳米碳管的C-C共价键是自然界当中具有稳定特征的化学键，无论在理论计算还是实践当中，都能够看出来，碳纳米管具有非常强的韧性。

在制备过程当中，碳纳米管主要涉及的电弧放电、催化热解和激光蒸发等。

具体来讲，在电弧放电当中，主要制备单壁碳纳米管，但是其中具有一定的弊端，比如产率非常低，但是成本却很高；而催化热解法当中所表现出来的是设备简单和生长速度较快等特点，一般在现代工程的批量化生产过程当中，会用到这种方法。

在当前应用领域，高强度的微米级碳纤维复合材料有着非常广阔的应用前景和较好的应用效果。

但是当前我国在这一领域所取得的进展依旧比较滞后，要想在强度上取得新的突破，必须要有效减少碳纤维的直径，提高纵横比。

碳纳米管是比较典型的纳米材料，纵横比非常可观。

更为重要的是，从长度上来讲，纳米管对于复合材料的加工性能并没有非常明显的不良影响，使用这一材料能够有效聚合复合材料，改变传统加工当中的一些问题，增强复合材料的导电性能。

再加上纳米管当中所具备的结构优势，使得聚合物电导率提升的同时也不容易被改变性能[1]。

钛基体上碳纳米管的原位合成及其复合材料的制备与性能研究

钛基体上碳纳米管的原位合成及其复合材料的制备与性能研究Preparation and Properties Research of Titanium matrix composite reinforced with in-situ synthesized CNTs学科专业：材料学研究生：雷红指导教师：赵乃勤教授天津大学材料科学与工程学院二零一三年十二月独创性声明本人声明所呈交的学位论文是本人在导师指导下进行的研究工作和取得的研究成果，除了文中特别加以标注和致谢之处外，论文中不包含其他人已经发表或撰写过的研究成果，也不包含为获得天津大学或其他教育机构的学位或证书而使用过的材料。

与我一同工作的同志对本研究所做的任何贡献均已在论文中作了明确的说明并表示了谢意。

学位论文作者签名：签字日期：年月日学位论文版权使用授权书本学位论文作者完全了解天津大学有关保留、使用学位论文的规定。

特授权天津大学可以将学位论文的全部或部分内容编入有关数据库进行检索，并采用影印、缩印或扫描等复制手段保存、汇编以供查阅和借阅。

同意学校向国家有关部门或机构送交论文的复印件和磁盘。

（保密的学位论文在解密后适用本授权说明）学位论文作者签名：导师签名：签字日期：年月日签字日期：年月日摘要钛基复合材料具有低密度、高比强度、良好耐蚀性以及高温性能等优点，成为最具潜力的新一代航空航天用结构材料之一。

碳纳米管（CNTs）具有高比强度、高比模量以及优异的综合性能，被认为是金属基复合材料最理想的增强相。

要使CNTs的优异性能在复合材料中得到充分发挥，关键要实现其在金属基体上的均匀分散，与基体形成良好的界面结合，并避免材料成形过程中CNTs与基体的反应。

因此，探索CNTs/Ti复合材料新的制备方法，对于发展钛基复合材料在航空航天领域的应用具有重要的理论意义和实用价值。

本论文采用化学气相沉积法在钛基体表面原位合成均匀分散的CNTs，研究了催化剂与碳源种类、合成温度、合成时间、碳源气体与载气比例对合成的CNTs 结构、分布以及产率的影响，并探讨了CNTs的生长机理。

Characterizing the properties of carbon nanotubes

Characterizing the properties ofcarbon nanotubesCarbon nanotubes (CNTs) have been the subject of extensive research due to their unique structural, electronic, mechanical, and thermal properties. CNTs are cylindrical tubes of carbon atoms, having a diameter of a few nanometers and a length of several micrometers. The walls of CNTs are made of graphene sheets that are rolled up into cylinders, resulting in a seamless tube with a hollow core. The properties of CNTs depend on their diameter, length, chirality, and defects, which can be controlled during the synthesis process.One of the most important properties of CNTs is their high aspect ratio, which is the ratio of their length to diameter. CNTs can have aspect ratios of up to 100,000, which makes them the strongest known materials, with tensile strengths up to 63 GPa. The strength of CNTs comes from their sp2 hybridized carbon bonds, which make the tubes extremely stiff and resilient. CNTs are also highly flexible, and can bend and twist without breaking, enabling them to be used in a wide range of applications.Another important property of CNTs is their electrical conductivity. CNTs are excellent conductors of electricity, with an electrical conductivity of up to 1x107 S/m, which is higher than that of copper. The conductivity of CNTs is dependent on their diameter and chirality, with smaller diameter tubes being more conductive than larger diameter tubes. The high conductivity of CNTs makes them a promising material for electronic and optoelectronic applications, such as transistors, sensors, and solar cells.CNTs also possess exceptional thermal conductivity, which is the ability to conduct heat. CNTs have an extremely high thermal conductivity of up to 3500 W/mK, which is higher than that of any other known material. The high thermal conductivity of CNTs makes them ideal for use in thermal management applications, such as heat sinks and nanocomposites.Furthermore, CNTs are highly hydrophobic, meaning that they repel water. This property makes them useful in applications where water resistance is required, such as in coatings and membranes. CNTs are also resistant to chemical corrosion and oxidation, which makes them highly durable and long-lasting.However, CNTs also have some limitations that need to be addressed. One of the major challenges is their toxicity. While CNTs have shown great promise in medical applications, such as drug delivery and cancer therapy, their potential toxicity to cells and tissues is a cause of concern. Studies have shown that CNTs can cause lung damage and inflammation in rodents, raising questions about their safety for human use. Therefore, it is important to thoroughly evaluate the toxicity of CNTs before using them in biomedical applications.In conclusion, CNTs are a remarkable material with unique and exceptional properties that make them suitable for a wide range of applications. Their high strength, electrical and thermal conductivity, hydrophobicity, and chemical stability make them a promising material in the fields of electronics, energy, and healthcare. However, their potential toxicity needs to be addressed before they can be widely used in biomedical applications. Understanding the properties of CNTs is essential for developing new applications that can exploit their exceptional properties while minimizing their drawbacks.。

碳纳米管复合材料

碳纳米管复合材料碳纳米管（Carbon Nanotubes，简称CNTs）是由碳原子按照特定方式组合成的一种纳米材料，它的直径在纳米级别，长度可以达到数微米到数厘米的范围。

碳纳米管具有极高的比表面积、优异的导电性和导热性，以及良好的机械性能，因此被广泛应用于复合材料领域。

碳纳米管复合材料是将碳纳米管与其他材料（如金属、聚合物等）进行复合得到的材料。

碳纳米管可以作为增强相，加入到其他材料基体中，通过增强材料的力学性能、导电性能、导热性能等。

碳纳米管与基体材料之间的相互作用机制很复杂，但一般包括物理机械锚定和化学键结合两种方式。

碳纳米管复合材料在电子器件、航空航天、能源储存等领域具有广阔的应用前景。

碳纳米管复合材料在电子器件中的应用是一大热点研究方向。

由于碳纳米管具有优异的导电性能，使得它们成为替代传统铜线的理想材料。

与铜线相比，碳纳米管具有更高的电流密度承载能力和更快的电子传输速度。

此外，碳纳米管复合材料还可以在导电材料中形成连续网络，提高材料的导电性能。

这使得碳纳米管复合材料成为电子器件中高性能电极材料的候选者，如电池的电极、光伏材料中的导电层等。

此外，碳纳米管复合材料还具有良好的力学性能和导热性能，适用于航空航天领域的应用。

碳纳米管在复合材料中的加入可以增强材料的强度和刚度，并改善材料的耐磨性和耐腐蚀性。

对于航空航天结构件来说，强度和轻量化是两个重要的性能指标，碳纳米管复合材料的应用可以达到这两个指标的要求。

此外，碳纳米管具有优异的导热性能，利用碳纳米管复合材料的热传导特性，可以制备用于散热的材料。

热管理是电子器件和能源储存等领域的一大挑战，碳纳米管复合材料可以在材料中形成高效的热传导通道，提高材料的热传导性能，有助于解决热管理问题。

总的来说，碳纳米管复合材料是一种多功能的材料，具有优异的力学性能、导电性能和导热性能。

它在电子器件、航空航天、能源储存等领域有着广泛的应用前景。

然而，碳纳米管的制备和复合材料中的分散性等问题仍然存在挑战，需要进一步的研究和技术突破。

advanced function materials缩写

advanced function materials缩写AdvancedFunctionMaterials(AFMs)是指一类具有高级功能的材料，它们在现代工业生产中扮演着越来越重要的角色。

AFMs 具有很多独特的物理、化学和电子特性，这些特性使它们成为各种应用领域的理想材料。

在本文中，我们将探讨 AFM 的一些常见缩写及其含义。

1. OLED有机发光二极管 (Organic Light Emitting Diode) 是一种能够将电能转化为光能的 AFM。

它由一层有机材料构成，这些材料能够在电场的作用下发光。

OLED 具有很高的发光效率、饱和色彩和高对比度，因此被广泛应用于显示器、照明和广告牌等领域。

2. MEMS微电子机械系统 (Microelectromechanical Systems) 是一种能够将机械和电子元件集成在一起的 AFM。

它由微型机械装置、传感器和控制电路等组成。

MEMS 具有体积小、重量轻、功耗低的特点，被广泛应用于生物传感、医疗器械、汽车电子和航空航天等领域。

3. CNT碳纳米管 (Carbon Nanotube) 是一种由碳原子构成的 AFM，它具有非常好的导电、导热和机械特性。

CNT 具有很高的强度和模量，因此可以用于制造高强度的复合材料和纳米机械装置。

此外，CNT 还具有较好的光学特性和生物相容性，因此被广泛应用于纳米电子、生物医学和能源存储等领域。

4. GNR石墨烯纳米带 (Graphene Nanoribbon) 是一种由石墨烯材料裁剪而成的 AFM。

GNR 具有非常好的电学、光学和热学特性，可以用于制造高性能的纳米电子器件、传感器和储能材料。

此外，GNR 还具有很好的生物相容性和低毒性，因此也被广泛应用于生物医学和纳米材料领域。

总之，AFMs 是一类非常重要的材料，在现代工业和科技发展中扮演着越来越重要的角色。

通过了解 AFM 的缩写及其含义，可以更好地理解这些材料的特性和应用。

碳纳米管材料的微波吸收机理研究

碳纳米管材料的微波吸收机理研究引言：碳纳米管材料由于其独特的结构和性质，近年来在许多领域得到了广泛的应用。

其中，碳纳米管材料的微波吸收性能引起了人们的极大。

本文将详细介绍碳纳米管材料的微波吸收机理，并分析影响其微波吸收性能的因素及改善措施，最后对碳纳米管材料在微波领域的应用前景进行展望。

碳纳米管材料微波吸收机理：碳纳米管材料是一种由碳原子组成的纳米级管状结构材料，其微波吸收机理主要包括两个方面：介电损耗和磁损耗。

介电损耗主要是由于碳纳米管材料的电子极化作用，导致在微波磁场中产生感应电流，进而产生焦耳热能；而磁损耗则主要是由于碳纳米管材料的磁导率发生变化，引起磁滞损耗和涡流损耗。

实验表明，碳纳米管材料的介电常数和磁导率受其结构、直径、长度、取向等因素的影响，这些因素均可以对碳纳米管材料的微波吸收性能产生影响。

影响因素及其改善措施：影响碳纳米管材料微波吸收性能的因素主要包括以下几个方面：碳纳米管材料的结构、直径、长度、取向、环境温度、湿度等。

其中，碳纳米管材料的结构对其微波吸收性能影响最大。

因此，针对这些影响因素，可以采取以下改善措施：优化碳纳米管材料的结构，包括直径、长度、取向等，以提高其微波吸收性能；调节碳纳米管材料的成分，以改变其介电常数和磁导率；对碳纳米管材料进行表面改性处理，以提高其对微波的吸收能力；在碳纳米管材料中添加其他介质材料，以调节其微波吸收性能。

应用前景展望：碳纳米管材料在微波领域具有广泛的应用前景，主要包括以下几个方面：微波吸收材料：碳纳米管材料具有优异的微波吸收性能，可以应用于制造高性能的微波吸收材料，如吸波涂料、吸波贴片、吸波内衣等，有望在电磁防护领域发挥重要作用。

微波器件：碳纳米管材料具有优良的导电性和电磁屏蔽性能，可以应用于制造高性能的微波器件，如滤波器、双工器、谐振器、天线等。

雷达隐身技术：由于碳纳米管材料对微波具有优异的吸收性能，可以将其应用于雷达隐身技术中，有效降低目标的雷达反射面积，提高目标的隐身性能。

陶瓷碳纳米管复合材料的制备性能及韧化机理

第14卷　第2期2006年4月材　料　科　学　与　工　艺MATER I A LS SC I ENCE &TECHNOLOGYVol 114No 12Ap r .,2006陶瓷/碳纳米管复合材料的制备、性能及韧化机理沈　军1,张法明1,2,孙剑飞1(1.哈尔滨工业大学材料科学与工程学院,黑龙江哈尔滨150001,E 2mail:junshen@hit .edu .cn;2.中国科学院上海硅酸盐研究所,上海200050)摘　要:评述和讨论了碳纳米管增强陶瓷基复合材料的制备工艺,包括碳纳米管在陶瓷基体上的分散和材料的烧结成型,添加碳纳米管后材料力学性能、导电和导热等物理性能的改善以及韧化机理,指出碳纳米管在陶瓷材料基体上的均匀分散,碳纳米管在组织中存活,碳纳米管与陶瓷基体的界面结合状态是影响碳纳米管增强陶瓷基复合材料性能提高的关键.关键词:碳纳米管;陶瓷基复合材料;韧化机理;力学性能;物理性能中图分类号:T B332文献标识码:A文章编号:1005-0299(2006)02-0165-06prepara ti on,properti es and tough i n g m echan is m s of carbonnanotubes re i n forced ceram i c ma tr i x co m positesSHEN Jun 1,Z HANG Fa 2m ing1,2,S UN J ian 2fei1(1.School of Materials Science and Engineering,Harbin I nstitute of Technol ogy,Harbin 150001,China,E 2mail:junshen@hit .edu .cn;2.Shanghai I nstitute of Cera m ics,Chinese Acade my of Science,Shanghai 200050,China )Abstract:Carbon nanotubes (CNTs )de monstrate excep ti onal p r operties and their unique tubular structures are believed t o be the ulti m ate reinf orce ment in composites .The mechanical and physical p r operties of brittle cera m ics could be i m p r oved by incor porating CNTs in the matrix .The p reparati on p r ocess for dis persi on of CNTs in the cera m ic matrix,sintering methods,mechanical p r operties,physical p r operties (such as electric conductivity and ther mal conductivity ),as well as t oughing mechanis m s in CNTs reinforced ceram ic matrix composites were revie wed and discussed .It is p r oposed that the key fact ors for i m p r oving the perf ora mce char 2acteristics of CNTs/cera m ic composites are unif or m distributi on of CNTs,the surviving of CNTs in the m icr o 2structures,and the interfacial bonding bet w een CNTs and the cera m ic matrix.Key words:carbon nanotubes;cera m ic matrix composites;t oughing mechanis m s;mechanical p r operties;physical p r operties收稿日期:2004-10-18.基金项目:国家自然科学基金资助项目(50374035).作者简介:沈　军(1965-),男,博士,教授,博士生导师;孙剑飞(1962-),男,博士,教授,博士生导师. 处于s p 2-3杂化态的碳元素可以形成多形态的结构,除金刚石和石墨外,晶态碳还可形成足球结构的C 60和一维管状的碳纳米管.碳纳米管可以看做由六边形的石墨板成360°卷曲而成的管状材料,管的内径在几纳米到几十纳米之间,长度可达微米甚至厘米尺度,长径比高达1000至10000,比表面积大,热稳定性高.在力学性能方面,碳纳米管强度、韧性高,延伸率、弹性模量大,耐磨性优良;尤其是单壁碳纳米管作为一种新型的自组装单分子材料,理论估算其杨氏模量高达5TPa,与金刚石相同,强度约为钢的100倍,而密度却只有钢的1/6,可能是目前比强度和比刚度最高的材料(见表1).碳纳米管还具有优异的导热性能和电学性能等物理特性.因此,碳纳米管被认为是最理想的纳米晶须增韧材料,是纤维类强化相的终极形式[1].陶瓷材料具有共价键和复杂离子键的键合以及复杂的晶体结构,因而呈现耐高温、耐磨损和重量轻等优异的性能,在航空航天,国防军工及工业生产等领域应用十分广泛,但陶瓷材料的脆性问题一直制约着其进一步发展和应用.通过引入增强介质,如第二相颗粒,纤维与晶须等合成陶瓷基复合材料来强韧化陶瓷材料的研究取得了一些成果,但增韧幅度不大.由于碳纳米管特殊的结构和优异的性能,合成碳纳米管增强的复合材料,已经在高分子基、金属基的材料中取得了显著的效果[2].目前,国内外对于碳纳米管增强高分子基复合材料的研究已经较系统,但碳纳米管增强陶瓷基复合材料的研究刚起步.本文对碳纳米管增强陶瓷基复合材料的制备(主要包括碳纳米管在基体上的分散和材料的烧结成型),复合材料的力学性能、物理性能的改善以及强韧化机理进行了评述,对研究中存在的问题进行了分析.表1　纤维材料的性能比较纤维直径/μm密度/(g・cm-3)拉伸强度/GPa弹性模量/GPa碳纳米管01001～0111133～212010～52400～5000碳纤维71166214～311120～170玻璃纤维72150314～41690尼龙纤维12114421870～170硼纤维100～1402150315400石英纤维9212031470碳化硅纤维10～202130218190碳化硅晶须0100231156194821　碳纳米管在陶瓷基体上的分散碳纳米管比表面积大,表面能高,碳管之间以较强的范德华力团聚在一起,尤其是有机物催化裂解法制备的碳纳米管经常弯曲缠绕在一起.此现象的产生将会减小碳纳米管的长径比,影响碳纳米管增强复合材料的增强效果.因此,如何将碳纳米管引入并均匀分散在基体上非常关键,碳纳米管的引入方式有原位自生法和外加混入法两种.111　原位自生碳纳米管Peigney等首先在A l2O3粉末基体上通过催化反应(Catalytic Method)[3]原位生长出碳纳米管网状束,发现在粉末中碳纳米管长约几十微米呈网络状较均匀的分布在粉末颗粒周围,经热压烧结后碳纳米管量比粉末中有所减少.Ka malakaran 等报道采用喷雾热解工艺[4]在A l2O3基体上原位生长了碳纳米管,发现纳米管在基体上分布很均匀,样品为2～4c m2的薄片,而且此种工艺还可优化制备出碳纳米管原位增强的陶瓷薄膜.Rul等采用凝胶泡沫法[5]在Co-Mg A l2O4氧化物固溶体基体上原位自生了碳纳米管,发现此种工艺碳纳米管产量很高,而且70%以上为单壁碳管, 95%以上为单壁和双壁碳纳米管;他们还在尖晶石(Mg A l2O4)基体上通过CCVD[6]的方法原位生长了碳纳米管,发现原位自生的碳纳米管非常均匀的分布在基体上.112　外加混入碳纳米管11211　物理分散法物理分散法指利用物理作用力将碳纳米管分散开,包括超声波法,球磨法,研磨法,高速剪切法等.但有学者认为物理方法只能分开碳纳米管的团聚体,而且会破坏碳纳米管[7];超声波法会使纳米管变短,随着分散时间延长碳管外壁会剥落,导致管壁变薄[8],而且只能够分散单一的团聚体,不能分散大团聚体[9];球磨和研磨等物理方法只能够将碳纳米管大块的团聚体分散成为小团聚体[9].清华大学L i等[10]对碳纳米管与颗粒尺寸为1μm铁粉混合进行了不同时间的震动球磨处理,磨球为直径不一的钢球,发现球磨15m in,许多碳纳米管端头破坏,而且有许多巴基葱颗粒出现,高能球磨60m in后,大部分碳纳米管变成了无定形碳,铁粉可以看作微小的磨球,其加入促进了碳纳米管的结构转变.11212　化学分散法化学分散法是指利用表面活性剂、表面改性剂或表面功能化来改变碳纳米管的表面能,提高其润湿或粘附特性,降低其在连续溶剂中的团聚倾向.(1)酸处理:采用浓H2S O4/HNO3混合溶液酸处理可以将碳纳米管完全分散开,原因是碳纳米管在酸处理过程中会变短而且增加亲水性官能团如羟基官能团等[9];如果采用浓硝酸处理后,碳纳米管的长度变短,管身变直,管壁上有—OH,>C—O和—COOH功能性官能团吸附,碳管在溶液中分散很均匀[11].Shaffer等也发现通过对催化裂解生长的碳纳米管进行酸氧化处理(HNO3:H2S O4=1:3)会给纳米管表面增加酚基和羟基官能团,这些官能团的存在可以使碳管以较高的浓度在水中稳定分散[12].(2)添加表面活性剂:添加表面活性剂如次乙亚胺(Ethyleni m ine)或者十二烷基硫酸钠(S DS)可以将碳纳米管在水溶液中均匀分散,通过溶胶杂凝聚的工艺,由于不同成分间静电相互作用,可以得到氧化钛和氧化铝颗粒包覆的碳纳米管[13];添加聚乙烯胺和阴离子柠檬酸于水溶液中作为分散剂对碳纳米管表面进行改性处理,然后在NH3中热处理,金纳米粒子可以吸附并填充到纳米管上表面和内部[14].在酒精溶液中添加20d mb%的共聚物作为分散剂可以成功的将110wt.%多壁碳纳米管均匀的分散开[15];在水・661・材　料　科　学　与　工　艺第14卷　中添加溴化十六烷基三甲铵(C 16T MAB )或聚丙烯酸(P AA )或C 16EO 作为分散剂都可以将碳纳米管均匀分散开,但不可能得到绝对的均匀[16].研究发现,添加阴离子表面活性剂十二烷基硫酸钠和阳离子表面活性剂柠檬酸铵都可以将碳纳米管较均匀的分散在水溶液中,阴、阳离子表面活性剂均以纳米颗粒的形式均匀的吸附在碳纳米管的表面上,如图1所示.图1　碳纳米管表面活化后的TE M 形貌11213　物理化学分散法物理化学分散法是将物理方法,如超声波法、球磨法等,与化学方法,如酸处理、添加表面活性剂等进行组合,以期达到将纳米管更加均匀分散在基体上的目的.采用添加表面活性剂与超声波振荡和球磨工艺结合,可将碳纳米管较均匀的分布在纳米WC /Co 粉末中[17].2　碳纳米管增强陶瓷基复合材料的烧结成型碳纳米管增强陶瓷基复合材料大部分采用烧结成型,通常制备纳米陶瓷材料和陶瓷基复合材料的工艺均可以用于制备碳纳米管增强陶瓷基复合材料,但烧结气氛必须是真空或惰性气体保护,以防止碳纳米管的氧化,碳纳米管在陶瓷烧结后组织中的存活状况非常重要.(1)热压烧结:热压烧结是最常用的一种制备碳纳米管增强陶瓷基复合材料的烧结工艺,采用热压烧结工艺所制备的碳纳米管增强的复合材料有Si C,Si O 2,A l 2O 3,Fe -A l 2O 3,Fe /Co -Mg A l 2O 4,Co -Mg O 基等材料[18～22],复合材料的性能均有所提高但不大.(2)烧结-热等静压:Balazsi 等采用烧结-热等静压(Sinter -H I P )烧结工艺制备了多壁碳纳米管增强Si 3N 4基复合材料,复合材料的弯曲强度和弹性模量均有可观的提高[23].(3)放电等离子烧结:放电等离子烧结(Spark Plas ma Sintering,简称SPS )是近年来发展起来的一种新型的烧结工艺,该系统利用脉冲能、放电脉冲压力和焦耳热产生的瞬时高温场来实现烧结过程,它在粉末之间能瞬时产生放电等离子体,使被烧结体内部每个颗粒均匀的自身发热,并且使颗粒表面活化更易于烧结;同时,烧结时在样品两端施加轴向压力,可以使烧结体更加致密和烧结温度降低.可以在极快的升温速度、低的烧结温度、极短的保温时间、较高的烧结压力下制得致密的块状纳米材料.有学者认为采用热压烧结工艺制备碳纳米管增强陶瓷基的复合材料,由于所需的烧结温度较高,保温时间较长,会对复合材料中的碳纳米管造成破坏,因此会降低甚至会丧失增韧效果[24].放电等离子烧结是非常有发展前景的制备碳纳米管增强陶瓷基复合材料的工艺.(4)其他工艺:Peigney 等采用高温挤压成型制备了碳纳米管增强金属氧化物复合材料,发现由于碳纳米管的引入,复合材料的超塑性成型更易进行,碳纳米管抑制了基体晶粒长大,并具有润滑介质的作用.研究发现,将碳纳米管在陶瓷材料基体上定向排列是可能的,通过控制碳纳米管的含量来调制纳米复合材料的导电性能[22].3　碳纳米管增强陶瓷基复合材料的性能改善将碳纳米管添加到陶瓷材料基体上,由于碳纳米管的分散程度和制备工艺的差别,导致复合材料的力学性能提高不一,有的甚至降低.除了力学性能外,碳纳米管增强陶瓷基复合材料的物理性能,如导电性能、导热性能均有较大的改善.311　力学性能1998年清华大学Ma 等首先尝试了在纳米Si C 陶瓷的基体上添加多壁碳纳米管,其断裂韧性仅提高了10%[18].Flahaut 等通过在Fe -A l 2O 3基体上原位生长碳纳米管,使复合材料的断裂强度比氧化铝稍有提高,但比Fe -A l 2O 3降低很多,其断裂韧性比纯氧化铝有所降低或相近[25].2001年Siegel 等报道在氧化铝基体上添加10vol%的多壁碳纳米管,其断裂韧性比纯氧化铝提高了24%[26].2003年Nature 发表了华人Zhan 等[24]的研究结果,他们在纳米A l 2O 3基体上添加10vol%的单壁碳纳米管,于1150℃放电等离子烧结(SPS )3m in 得到的复合材料的维氏硬度达到了・761・第2期沈　军,等:陶瓷/碳纳米管复合材料的制备、性能及韧化机理1611GPa,断裂韧性K I C达到了917MPa・m1/2,约为单纯纳米氧化铝材料的3倍,为迄今增韧效果最佳的报道.Balazsi等研究了碳纳米管与碳纤维、碳黑和石墨复合Si3N4陶瓷的增韧效果,发现Si3N4-CNTs的力学性能比其他碳材料如碳纤维、碳黑和石墨复合Si3N4提高了15%～37%[23].An等对A l2O3-CNTs复合材料的摩擦学特性进行了研究,发现添加4wt%以内的碳纳米管可以提高材料的耐磨性能[27].2004年中科院上硅所N ing等在Si O2添加5vol%的多壁碳纳米管,由于碳纳米管较均匀的分散,添加了5v ol.%的碳纳米管的Si O2弯曲强度和断裂韧性分别提高了88%与146%,而不添加分散剂的5v ol.%CNTs-Si O2复合材料的力学性能提高较少[16].我课题组采用放电等离子烧结工艺制备了纳米WC-Co-CNTs复合材料,研究发现复合材料的硬度和断裂韧性可以同时提高,硬度和断裂韧性比不添加碳纳米管的纳米WC-Co硬质合金分别提高了17%和35%[17],起到了强韧化效果. 312　物理性能单壁纳米碳管的室温纵向电导率达106S/m, Zhan等后续的研究结果表明,S WCNT/A l2O3的导电性能随着碳纳米管含量的增加而提高, 15vol%S WCNT/A l2O3的导电率达3345S/m[28]. Flahaut碳纳米管可以使其由绝缘体变为导体,电导率在012～410S/m,电导率的值与组织中碳纳米管的破坏程度有关,当管结构完全破坏时,就不再导电[29].单独一根多壁纳米碳管的室温热导率预计达3000W/mK,单独一根单壁碳纳米管室温热导率达6000W/mK,而单壁碳纳米管束的室温热导率大于200W/mK[30],碳纳米管被认为是目前世界上最好的导热材料.N ing等随后的研究发现在Si O2的基体上添加碳纳米管,材料的热扩散系数和热导率随着碳纳米管的含量的增加而增大,在650℃含10vol%碳纳米管的Si O2的热扩散系数和导热率分别提高了1613%和2016%[31].4　碳纳米管增强陶瓷基复合材料的强韧化机理有关研究发现,在碳纳米管增强纳米陶瓷基复合材料中,碳纳米管可以在一定程度抑制纳米陶瓷晶粒长大,并促进陶瓷致密度的提高,使材料强度提高.Zhan等在单壁纳米碳管增强纳米氧化铝基复合材料中,发现碳纳米管包围在纳米氧化铝晶粒周围,有效地抑制了晶粒的长大[24].中科院金属所的钟等在碳纳米管增强纳米铝基复合材料制备过程中发现碳纳米管具有阻止纳米A l晶粒长大的作用[32].碳纳米管的引入会与基体产生界面反应,清华大学Xu等[33]发现,A l/CNTs复合材料的界面形成了A l C和A l C2脆性碳化物,消弱了界面的结合强度.浙江大学吴等[34]对含有微量碳纳米管的纳米WC-Co硬质合金做了初步研究,发现碳纳米管与WC粒子形成了W-C化学键,强化了界面结合.我课题组对纳米WC-Co-CNTs硬质合金材料的研究表明,添加适量的碳纳米管在纳米WC-Co基体上,在烧结过程中碳纳米管可以填充显微空隙,以及碳纳米管的添加引起合金中碳含量的稍微提高,致使液相量增加从而促进了烧结致密化进程;碳纳米管与WC晶界相互作用可以一定程度上抑制纳米WC的晶粒长大,所以材料的硬度和韧性同时提高[17].对于微米级纤维复合的陶瓷材料,增韧机理有桥联增韧,裂纹偏转增韧,拔出效应.Ma认为在纳米Si C-10%CNTs中断裂韧性提高是由于碳纳米管的裂纹偏转和拔出效应造成的[18].N ing报道碳纳米管增强Si O2复合材料中桥联、裂纹偏转和拔出效应都起作用[19].Zhan[24]发现:纳米A l2O3 -10vol%S WCNTs复合材料的裂纹扩展路径仍然呈沿晶断裂,没有发现桥联和拔出现象,认为碳管拔出是由于碳管与基体结合不牢固造成的,他认为其性能大幅度提高是由于单壁碳纳米管比多壁管力学性能和结构更加优异,单壁碳管呈网络状连续的环绕在纳米氧化铝晶粒周围造成了裂纹的偏转,增韧如图2所示,箭头所指为碳纳米管;放电等离子烧结的低温短时没有造成单壁碳纳米管的破坏等原因引起的.Xia等[35]在氧化铝基体上原位定向生长了多壁碳纳米管,制备出20μm和90μm厚的涂层材料,经纳米硬度计和扫描电镜分析发现,在微米级纤维增强的陶瓷基复合材料中的增韧机制,在碳纳米管增强陶瓷基复合材料中仍然都存在,而且呈现了新的机制,碳纳米管在图2　单壁碳纳米管增强纳米氧化铝基复合材料・861・材　料　科　学　与　工　艺第14卷　剪切带附近产生倒塌而不产生裂纹,说明此材料具有多向破坏承受能力,三维有限元分析表明,碳纳米管增强的氧化铝陶瓷基复合材料基体上的残余应力达300MPa,提高了材料的工程使用性能.对放电等离子烧结制备的纳米WC-Co-CNTs 复合材料的增韧机理初步研究发现,烧结后碳纳米管仍然存活在组织中,断裂面上存在着碳纳米管桥联和拔出增韧现象[17].5　研究中存在的问题1)碳纳米管在基体上分散效果和状态直接影响复合材料的性能提高,原位自生法与外加混入法相比,能够得到纳米管在基体上更加均匀的分布,但技术设备要求高.迄今为止,如何将碳纳米管在不破坏或少破坏其完美结构的前提下非常均匀的分散到陶瓷材料基体上,仍有待深入研究.2)烧结成型是碳纳米管增强陶瓷基复合材料制备过程中的最后也是关键的一步,保证碳纳米管在组织中的存活十分重要.低温、短时、快速烧结工艺———放电等离子烧结,可以在保持碳纳米管在陶瓷组织中的完整性,较适合制备碳纳米管增强陶瓷基复合材料.但放电等离子烧结的内在烧结机制,以及碳纳米管复合的纳米材料在SPS工艺下的烧结动力学机理有待研究.3)采用碳纳米管复合陶瓷材料不仅可以改善材料的力学性能,还可以增加其功能特性,如导电性能、导热性能等,并且可以通过碳纳米管含量和排列方向的控制来对陶瓷材料的性能进行调制.碳纳米管还具有波吸收特性、场致发射性能等,制备高力学性能兼多功能化的陶瓷材料,碳纳米管是最理想的增强纤维选择.但目前碳纳米管较昂贵,如何大幅度地提高复合材料的性能,提高材料的性价比,并达到性能可预测、可控制,有待于深入研究.6　结　语碳纳米管具有优异的力学性能,电学性能和导热性能等物理性能,极高的长径比以及独特的一维管状纳米结构,碳纳米管复合材料的研究已成为碳纳米管应用研究的重要方向和国内外的研究热点.引入碳纳米管来复合陶瓷材料有望进一步提高陶瓷材料的力学性能,同时增加其功能特性,实现结构功能一体化,并且通过对碳纳米管的排列和含量控制可以对陶瓷材料的性能进行调制.碳纳米管在陶瓷材料基体上的增强效果主要取决于碳纳米管在陶瓷材料基体上的分散程度,碳纳米管在组织中的存活,及碳纳米管与陶瓷基体的界面结合状态等因素.碳纳米管增强陶瓷基复合材料在纳米尺度上的成型、特性、破坏和强韧化机制的研究将大大丰富陶瓷材料的研究内容,并将为进一步拓宽陶瓷材料作为先进材料的应用范畴奠定基础.参考文献:[1]DA I H.Carbon nanotubes:opportunities and challenges[J].Surface Science,2002,500:218-241.[2]LAU K T,DAV I D H.The revoluti onary creati on of ne wadvanced materials2carbon nanotube composites[J].Composites:Part B,2002,33:263-277.[3]PE I G NEY A,LAURE NT Ch,ROUSSET A.Synthesisand characterizati on of alu m ina matrix nanocomposites containing carbon nanotubes[J].Key Engineering M a2 terials,1997,743-746:132-136.[4]K AMALAK ARAN R,LUP O F,GROBERT N.I n2situfor mati on of carbon nanotubes in an alu m ina2nanotube composite by s p ray pyr olysis[J].Carbon,2003,41:2737-2741.[5]RUL S,LAURE NT Ch,PE I G NEY A,et a l.Carbonnanotubes p repared in situ in acellular cera m ic by the gelcasting f oa m method[J].Journal of the Eur opean Ceram ic Society,2003,23:1233-1241.[6]RUL S,LEFE VRESCHL I CK F,C APR I A E,et a l.Per2colati on of single2walled carbon nanotubes in ceram ic matrix nanocomposites[J].Acta M aterialia,2004,52:1061-1067.[7]H I L D I N G J,GRULKE E A,Z HANG Z G,et a l.D is2persi on of carbon nanotubes in liquids[J].Journal ofD is per Sci Technol,2003,24(1):1-41.[8]LU K L,LAG O R M,CHE N Y K,et a l.M echanicalda mage of carbon nanotubes by ultras ound[J].Car2 bon,1996,34:814-816.[9]WANG Yao,WU Jun,W E I Fei.A treat m ent method t ogive separated multi2walled carbon nanotubes with high purity,high crystallizati on and a large as pect rati o[J].Carbon,2003,41:2939-2948.[10]L I Y B,W E IB Q,L I A NG J,et a l.Transfor mati on ofcarbon nanotubes t o nanoparticles by ball m illingp r ocess[J].Carbon,1999,37:493-497.[11]J I A Z,WANG Z,L I A NG J,et a l.Pr oducti on of shortmulti2walled carbon nanotubes[J].Carbon,1999,37:903-906[12]SHAFFER M S P,F AN X,W I N DLE A H.D is persi onand Packing of Carbon Nanotubes[J].Carbon,1998,36(11):1603-1612.[13]S UN J,G AO L.Devel opment of a dis persi on p r ocessf or carbon nanotubes in cera m ic matrix by heter ocoagu2lati on[J].Carbon,2003,41:1063-1068.・961・第2期沈　军,等:陶瓷/碳纳米管复合材料的制备、性能及韧化机理[14]J I A NG L,G AO L.Modified carbon nanotubes:an ef2fective way t o selective attach ment of gold nanoparticles[J].Carbon,2003,41:2923-2929.[15]Z HAO L,G AO L.Stability of multi2walled carbonnanotubes dis persi on with copoly mer in ethanol[J].Coll oids and Surfaces A,2003,224:127-134. [16]N I N G J,Z HANG J,P AN Y,et al.Surfactants assistedpr ocessing of carbon nanotube reinf orced Si O2matrix co m2 posites[J].Cera mics I nternati onal,2004,30:63-67. [17]Z HANG F,S HE N J,S UN J.Pr ocessing and p r operties ofcarbon nanotubes2nano2WC2Co co mposite[J].MaterialsScience&Engineering A,2004,381(1-2):87-92. [18]MA R Z,WU J,W E IB Q,et a l.Pr ocessing and p r op2erties of carbon nanotubes2nano2Si C cera m ic[J].Journal ofM aterials Science,1998,33:5243-5246.[19]N I N G J,ZHANG J,P AN Y,et a l.Fabricati on and me2chanical p r operties of Si O2matrix composites reinf orcedby carbon nanotubes[J].M aterials Science&Engi2 neering A,2003,357(1-2):392-396.[20]CHANG S,DORE MUS R H,AJAY AN P M.Pr ocess2ing and mechanical p r operties of carbon nanotube rein2 forced alu m ina composites[J].Cera m ic Engineeringand Science Pr oceedings,2000,21(3):653-658. [21]PE I G NEY A,LAURE NT Ch,F LAJAUT E,et a l.Car2bon nanotubes in novel cera m ic matrix nanocomposites[J].Cera m ics I nternati onal,2000,26:677-683. [22]PE I G NEY A,F LAHAUT E,LAURE NT Ch,et a l.A2ligned carbon nanotubes in cera m ic2matrix nanocompos2ites p repared by high2temperature extrusi on[J].Chem ical Physics Letters,2002,352:20-25. [23]BALAZSI Cs,K ONY A Z,W E BER F,et a l.Prepara2ti on and characterizati on of carbon nanotube reinf orcedsilicon nitride composites[J].Materials Science&Engineering C,2003,23:1133-1137.[24]ZHAN G D,K UNTZ J D,WAN J,et a l.Single2wallcarbon nanotubes as attractive t oughing agents in alu m i2 na2based nanocomposites[J].Nature Materials,2003,2:38-42.[25]LAURE NT Ch,PE I G NEY A,DUMORTI ER O,et a l.Carbon nanotubes2Fe2A lu m ina nanocomposites.PartII:m icr ostructure and mechanical p r operties of the hot2 Pressed composites[J].Journal of the Eur opean Ce2ra m ic Society,1998,18(14):2005-2013.[26]SI EGE L R W,CHANG S K,ASH B J.Mechanical be2havi or of poly mer and cera m ic matrix nanocomposites[J].Scri p ta M aterialia,2001,44:1472-1475. [27]AN J W,Y OU D H,L I M D S.Tribol ogical p r opertiesof hot2p ressed alu m ina2C NT composites[J].W ear,2003,255(1-6):677-681.[28]ZHAN G D,K UNTZ J D,G ARAY J E.Electricalp r operties of nanocera m ics reinf orced with r opes of sin2gle walled carbon nanotubes[J].App lied Physics Let2ters,2003,83(6):1228-1230.[29]F LAHAUT E,PE I G NEY A,LAURE NT Ch,et a l.Car2bon nanotube2metal2oxide nanocomposites:M icr ostruc2ture,Electrical conductivity and mechanical p r operties[J].Acta Materialia,2000,48:3803-3812. [30]B I ERUK M J,L I A G UNO M C,RADOS AV I JE V I C M.Carbon nanotube co mposites f or ther malmanage ment[J].Applied Physics Letters,2002,80(15):2767-2769. [31]N I N G J,ZHANG J,P AN Y,et a l.Fabricati on andther mal p r operties of carbon nanotube/Si O2composites[J].Journal of Materials Science Letters,2003,22:1019-1021.[32]钟　蓉,丛红涛,成会明,等.单壁纳米碳管增强纳米铝基复合材料的制备[J].材料研究学报,2002,16(4):344-348.[33]XU C L,W E IB Q,MA R Z,et a l.Fabricati on of alu2m inu m2carbon nanotubes and their electrical p r operties[J].Carbon,1999,37(5):855-858.[34]吴希俊,谭国龙.纳米碳化钨-钴-碳化钒硬质合金的制备方法及设备[P].中国专利:1240639,2000-01-19.[35]X I A Z,R I ESTER L,C URTI N W A.D irect observati onof t oughing mechanis m s in carbon nanotube ceram icmatrix composites[J].Acta Materialia,2004,52:931-944.(编辑　吕雪梅)(上接第164页)[4]王成莲,刘　莉.比色法测定抗坏血酸体系产生的・OH[J].生物化学与生物物理进展,1989,16(6): 473-475.[5]JE N J F,LE LL M F,T HOMAS C Y.Deter m inati on ofhydr oxyl radicals in an advanced oxidati on p r ocess with salicylic acid trapp ing and liquid chr omat ography[J].Journal of Chr omat ography A,1998,796:283-288. [6]金　鸣,蔡亚欣,李金荣,等.邻二氮菲-Fe2+氧化法检测H2O2/Fe2+产生的羟自由基[J].生物化学与生物物理进展,1996,23(6):543-553.[7]张乃东,郑　威.UV-V is-草酸铁络合物-H2O2体系产生羟自由基的Fe(phen)32+光度法测定[J].分析测试学报,2002,21(5):36-39.[8]L I X Z,F AN C M,S UN Y P.Enhancement of phot ocata2lytic oxidati on of hu m ic acid in Ti O2sus pensi on by in2creasing i on strength[J].Che mos phere,2002,48(4):453-460.(编辑　吕雪梅)・71・材　料　科　学　与　工　艺第14卷　。

美国Hyperion Catalysis碳纳米管

Hyperion Catalysis International, Inc.美国Hyperion(海博龙) Catalysis International(HCI)是碳纳米管技术发展与商业化应用的世界领导者。

成立于1982年的海博龙最早开发了一种新颖结构和形态的碳，海博龙的旗舰技术是导电的、蒸发生长的多壁碳纳米管。

这些管的商品命名为FIBRIL™碳纳米管。

从1983年最初合成碳纳米管，海博龙全力专注于改进碳纳米管的结构技术和开拓各种应用领域。

海博龙现在可以提供塑料领域的碳纳米管及预混料，这些塑料与碳纳米管的复合材料已经商业化应用于不断增长的汽车与电子工业领域。

由于碳纳米管独特的结构，FIBRIL™碳纳米管也用于高附加值导电塑料制品。

另外, FIBRIL™碳纳米管的应用在不断地发展，并希冀开拓出广阔的、令人兴奋的市场。

我们真诚地欢迎您联系我们，探讨如何利用碳纳米管为您设计研发出杰出的产品。

碳纳米管在不同塑料中的分散非常困难，为了确保碳纳米管分散的一致与均匀性，获得高质量的产品，海博龙使用FIBRIL™碳纳米管只提供塑料领域的系列母料与专用料，客户需要其他形式的特殊产品，请与客服联系。

这些母料的重量浓度典型值为15-20%，使用时必须稀释到最终的浓度。

母料的稀释非常重要，须仔细而彻底，高粘度的母料与低粘度的稀释树脂会造成分散不均匀。

两相混合结构可以比喻成小“岛相”的母料分散在大“海相”树脂中，这些母料小岛是微米级尺寸的、球形的导电添加剂，而不是纳米级的、高长径比的纳米管。

中山百能思塑料科技有限公司Zhongshan BALANCE Plastics Science & Technology Co., Ltd.广东省中山市火炬开发区港义路1号公司网址： Hyperion Catalysis International is the world leader in carbon nanotube development and commercialization.The Leader in Nanotube Technology美国Hyperion(海博龙)----碳纳米管技术的世界领导者广州百能思化工科技有限公司Guangzhou BALANCE Chemical Science & Technology Co., Ltd.广东省广州市番禺区大石街朝阳东路166号公司网址：FIBRIL™碳纳米管母料系列产品ProductsAmorphousBase Resin Grade Name Polystyrene (PS) MB2020-00 Polycarbonate (PC) MB6015-00 Polyetherimide (PEI) MB8515-02 Semi-CrystallineBase Resin Grade Name Ethylene Vinyl Acetate (EVA)MB2525-00 Polypropylene (PP) MB3020-01 High Density Polyethylene (HDPE)MB3520-00 Polyethylene Terephthalate (PET)MB6815-00 Polybutylene Terephthalate (PBT)MB5015-00 Nylon (Polyamide) 6 (PA6)MB4020-00 Nylon (Polyamide) 6,6 (PA66)MB4620-00 Nylon (Polyamide) 12 (PA12)MB4220-00 Polyetheretherketone (PEEK) MB9015-00 Polyphenylene Sulfide (PPS)MB7015-00 FluoropolymerBase Resin Grade Name Ethylene Tetrafluoroethylene (ETFE)MB9315-00BALANCE®科技----专注于高分子材料助剂的应用技术服务宗旨：只为客户提供优质产品经营理念：品质源于专业，发展始于共赢FIBRIL™碳纳米管专用料系列Antistatic Grades have a volume resistivity of 10E8 to 10E10 ohm cm. Electrostatic Dissipative Grades have a volume resistivity of 10E4 to 10E6 ohm cm. Conductive Grades have a volume resistivity of 10E0 to 10E2 ohm cm.ProductsAmorphousResinGradeName Polycarbonate - Antistat Grade HC-609 Polycarbonate - Electrostatic Dissipative Grade HC-605 Polycarbonate - Conductive Grade HC-601 Polyetherimide - Antistat Grade HC-859 Polyetherimide Electrostatic Dissipative Grade HC-855 Polyetherimide Conductive Grade HC-851 Semi-CrystallineResinGradeName Polypropylene - Antistat Grade HC-309 Polypropylene - Electrostatic Dissipative Grade HC-305 Polypropylene - Conductive Grade HC-301 Polybutylene Terephthalate - Antistat Grade HC-509 Polybutylene Terephthalate - Electrostatic Dissipative Grade HC-505 Polybutylene Terephthalate - Conductive Grade HC-501 Nylon (Polyamide) 12 - Antistat Grade HC-429 Nylon (Polyamide) 12 - Electrostatic Dissipative Grade HC-425 Nylon (Polyamide) 12 - Conductive Grade HC-421 Nylon (Polyamide) 6,6 - Antistat Grade HC-469 Nylon (Polyamide) 6,6 - Electrostatic Dissipative Grade HC-465 Nylon (Polyamide) 6,6 - Conductive Grade HC-461 Polyphenylene Sulfide - Electrostatic Dissipative Grade HC-705 Polyphenylene Sulfide - Conductive Grade HC-701 Polyetheretherketone - Antistat Grade HC-909 Polyetheretherketone - Electrostatic Dissipative Grade HC-905 Polyetheretherketone - Conductive Grade HC-901 FluoropolymerResinGradeName Ethylene Tetrafluoroethylene - Electrostatic Dissipative Grade HC-935 Ethylene Tetrafluoroethylene - Conductive Grade HC-931 Polyvinylidene Fluoride - Electrostatic Dissipative Grade HC-325 Polyvinylidene Fluoride - Conductive Grade HC-321。

High-pressure vibrational and optical study of Bi(2)Te(3)

PHYSICAL REVIEW B84,104112(2011)High-pressure vibrational and optical study of Bi2Te3R.Vilaplana,1,*O.Gomis,1F.J.Manj´o n,2A.Segura,3E.P´e rez-Gonz´a lez,4P.Rodr´ıguez-Hern´a ndez,4A.Mu˜n oz,4 J.Gonz´a lez,5,6V.Mar´ın-Borr´a s,3V.Mu˜n oz-Sanjos´e,3C.Drasar,7and V.Kucek71Centro de Tecnolog´ıas F´ısicas,MALTA Consolider Team,Universitat Polit`e cnica de Val`e ncia,46022Valencia,Spain 2Instituto de Dise˜n o para la Fabricaci´o n y Producci´o n Automatizada,MALTA Consolider Team,Universitat Polit`e cnica de Val`e ncia,46022Valencia,Spain3Instituto de Ciencia de Materiales de la Universidad de Valencia—MALTA Consolider Team—Departamento de F´ısica Aplicada,Universitatde Val`e ncia,46100Burjassot,Valencia,Spain4MALTA Consolider Team—Departamento de F´ısica Fundamental II and Instituto Universitario de Materiales y Nanotecnolog´ıa,Universidad de La Laguna,La Laguna,Tenerife,Spain5DCITIMAC,MALTA Consolider Team,Universidad de Cantabria,Avda.de Los Castros s/n,39005Santander,Spain6Centro de Estudios de Semiconductores,Universidad de los Andes,M´e rida5201,Venezuela7Faculty of Chemical Technology,University of Pardubice,Studentsk´a95,53210-Pardubice,Czech Republic(Received8June2011;revised manuscript received25July2011;published9September2011)We report an experimental and theoretical lattice dynamics study of bismuth telluride(Bi2Te3)up to23GPa together with an experimental and theoretical study of the optical absorption and reﬂection up to10GPa.The indirect bandgap of the low-pressure rhombohedral(R-3m)phase(α-Bi2Te3)was observed to decrease withpressure at a rate of−6meV/GPa.In regard to lattice dynamics,Raman-active modes ofα-Bi2Te3were observedup to7.4GPa.The pressure dependence of their frequency and width provides evidence of the presence of anelectronic-topological transition around4.0GPa.Above7.4GPa a phase transition is detected to the C2/mstructure.On further increasing pressure two additional phase transitions,attributed to the C2/c and disorderedbcc(Im-3m)phases,have been observed near15.5and21.6GPa in good agreement with the structures recentlyobserved by means of x-ray diffraction at high pressures in Bi2Te3.After release of pressure the sample reverts backto the original rhombohedral phase after considerable hysteresis.Raman-and IR-mode symmetries,frequencies,and pressure coefﬁcients in the different phases are reported and discussed.DOI:10.1103/PhysRevB.84.104112PACS number(s):61.50.Ks,62.50.−p,78.20.Ci,78.30.−jI.INTRODUCTIONBismuth telluride(Bi2Te3)is a layered chalcogenide with a tremendous impact for thermoelectric applications.1The thermoelectric properties of Bi2Te3and their alloys have been extensively studied due to their promising operation in the temperature range of300–400K.In fact Bi2Te3is the material with the best thermoelectric performance at ambient temperature.2,3Recently,it has been shown that Bi2Te3can be exfoliated like graphene and that a single layer exhibits high electrical conductivity and low thermal conductivity so that a new nanostructure route can be envisaged to improve dramatically the thermoelectrical properties of this compound by means of either charge-carrier conﬁnement or acoustic-phonon conﬁnement.4,5Bi2Te3is a narrow bandgap semiconductor with tetradymite crystal structure[R-3m,space group(S.G.)166,Z=3].6 This rhombohedral-layered structure is formed by layers, which containﬁve hexagonal close-packed atomic sublayers (Te-Bi-Te-Bi-Te)and is named a quintuple linked by van der Waals forces.The same layered structure is common to other narrow bandgap semiconductor chalcogenides,like Bi2Se3and Sb2Te3,and has been found in As2Te3at high pressures.7 Bi2Te3,as well as Bi2Se3and Sb2Te3,has been recently predicted to behave as a topological insulator8;i.e.,a new class of materials that behave as insulators in the bulk but conduct electrical current in the surface.The topological insulators are characterized by the presence of a strong spin-orbit(SO) coupling that leads to the opening of a narrow bandgap and causes certain topological invariants in the bulk to differ from their values in vacuum.The sudden change of invariants at the interface results in metallic,time-reversal invariant-surface states whose properties are useful for applications in spintronics and quantum computation.9,10Therefore,in recent years a number of papers have been devoted to the search of the 3D-topological insulators among Sb2Te3,Bi2Te3,and Bi2Se3, and different works observed the features of the topological nature of the band structure in the three compounds.11–13 High-pressure studies are very useful to understand mate-rials properties and design new materials because the increase in pressure allows us to reduce the interatomic distances and toﬁnely tune the materials properties.It has been veriﬁed that the thermoelectric properties of semiconductor chalcogenides improve with increasing pressure,and that the study of the properties of these materials could help in the design of better thermoelectric materials by substituting external pressure by chemical pressure.14–18Therefore,the electrical and thermoelectric properties of Sb2Te3,Bi2Te3,and Bi2Se3, as well as their electronic-band structure,have been studied at high pressures.19–27In fact a decrease of the bandgap energy with increasing pressure was found in Bi2Te3.19,20 Furthermore,recent high-pressure studies in these compounds have shown a pressure-induced superconductivity28,29that has further stimulated high-pressure studies.30However,the pressure dependence of many properties of these layered chalcogenides is still not known.In particular the determi-nation of the crystalline structures of these materials at high pressures has been a long puzzle15,23,31,32and the space groups of the high-pressure phases of Bi2Te3have been elucidatedR.VILAPLANA et al.PHYSICAL REVIEW B84,104112(2011)only recently by powder x-ray diffraction measurements at synchrotron-radiation sources33,34specially with the use of particle-swarm optimization algorithms for crystal-structure prediction.34Recent high-pressure powder x-ray diffraction measure-ments have evidenced a pressure-induced electronic topolog-ical transition(ETT)in Bi2Te3around3.2GPa as a changein compressibility.29,31,32,35,36An ETT or Lifshitz transitionoccurs when an extreme of the electronic-band structure,whichis associated to a Van Hove singularity in the density of states,crosses the Fermi-energy level.37This crossing,which canbe driven by pressure,temperature,doping,etc.,results in achange in the topology of the Fermi surface that changes theelectronic density of states near the Fermi energy.An ETTis a2.5transition in the Ehrenfest description of the phasetransitions so no discontinuity of the volume(ﬁrst derivativeof the Gibbs free energy)but a change in the compressibility(second derivative of the Gibbs free energy)is expected inthe vicinity of the ETT.Anomalies in the phonon spectrumare also expected for materials undergoing an ETT38,39andhave been observed in a number of materials40,41as well as inSb1.5Bi0.5Te3.31The lattice dynamics of Bi2Te3have been studied ex-perimentally at room pressure42–44and a recent study sug-gests that Raman spectroscopy can be used to monitorthe number of single quintuple layers in nanostructuredBi2Te3,as in graphene.45Theoretical studies of the lat-tice dynamics of Bi2Te3at room pressure have also beenperformed;46–49however,Raman measurements at high pres-sures have only been reported up to0.5GPa,50and to ourknowledge there is no theoretical study of the lattice dynamicsproperties of Bi2Te3under high pressure.As a part of oursystematic study of the structural stability and the vibrationalproperties of the semiconductor chalcogenide family,wereport in this work room-temperature Raman-scattering mea-surements in Bi2Te3up to23GPa together with total-energyand lattice-dynamical ab initio calculations at different pres-sures.We discuss the recent observation of a pressure-inducedETT in the rhombohedral phase ofα-Bi2Te3and study whetherthe Raman-scattering signal of the Bi2Te3at pressures above7.4GPa match with the proposed high-pressure phases recentlyreported for this compound33,34and which have also beenfound in Sb2Te3at high pressures.51II.EXPERIMENTAL DETAILSWe have used single crystals of p-type Bi2Te3that weregrown using a modiﬁed Bridgman technique.A polycrystallineingot was synthesized by the reaction of stoichiometricquantities of the constituting elements(5N).Afterward,thepolycrystalline material was annealed and submitted to thegrowth process in a vertical Bridgman furnace.Preliminaryroom-temperature measurements on single crystalline samples(15mm×4mm×0.3mm)yield in-plane electrical resistivityρ⊥c=1.7·10−5 m and Hall coefﬁcient R H(B c)= g0.52cm3C−1.Following the calculation presented in Ref.52,the latter gives hole concentration of7.2·1018cm−3andminority electron concentration of2.1·1017cm−3.A smallﬂake of the single crystal(100μm×100μm×5μm)was inserted in a membrane-type diamond anvil cell(DAC)with a4:1methanol-ethanol mixture as pressure-transmitting medium,which ensures hydrostatic con-ditions up to10GPa and quasihydrostatic conditions between 10and23GPa.53,54Pressure was determined by the ruby luminescence method.55Unpolarized room-temperature Raman-scattering measure-ments at high pressures were performed in backscattering geometry using two setups:(i)A Horiba Jobin Yvon LabRAM HR microspectrometer equipped with a TE-cooled multichan-nel CCD detector and a spectral resolution below2cm−1. HeNe laser(6328˚A line)was used for excitation.(ii)A Horiba Jobin Yvon T64000triple-axis spectrometer with resolution of1cm−1.In this case an Ar+laser(6470˚A line)was used for excitation.In order not to burn the sample,power levels below2mW were used inside the DAC.This power is higher than that used in Raman measurements at room pressure due to superior cooling of the sample in direct contact with the pressure-transmitting media and the diamonds.Optical transmission and reﬂection measurements under pressure were performed by putting the DAC in a home-built Fourier Transform infrared(FTIR)setup operating in the mid-IR region(400–4000cm−1).The pressure-transmitting medium was KBr.The setup consists of a commercial TEO-400FTIR interferometer by ScienceTech S.L.,which includes a Globar thermal-infrared source and a Michelson interferome-ter,and a liquid-nitrogen cooled Mercury-Cadmium-Telluride (MCT)detector with wavelength cutoff at25μm(400cm−1) from IR Associates Inc.A gold-coated parabolic mirror focuses the collimated IR beam onto a calibrated iris of1 to3mm diameter.A gold-coated X15Cassegrain microscope objective focuses the IR beam inside the DAC to a size of70–200μm.A second Cassegrain microscope objective collects the transmitted IR beam and sends it to the detector after being focused by another parabolic mirror.In the reﬂection conﬁguration,aﬂat gold mirror is placed at45◦before the focusing Cassegrain objective,blocking half of the IR beam. The half-beam let into the DAC is reﬂected by the sample, then by theﬂat gold mirror,andﬁnally focused on the MCT detector by another parabolic mirror.III.AB INITIO CALCULATIONSTwo recent works have reported the structures of the high-pressure phases of Bi2Te3up to52GPa.33,34The rhombohedral(R-3m)structure(α-Bi2Te3)is suggested to transform to the C2/m(β-Bi2Te3,S.G.12,Z=4)and the C2/c (γ-Bi2Te3,S.G.15,Z=4)structures above8.2and13.4GPa, respectively.34Furthermore,a fourth phase(δ-Bi2Te3)has been found above14.5GPa and assigned to a disordered bcc structure(Im-3m,S.G.229,Z=1).33,34In order to explore the relative stability of these phases in Bi2Te3we have performed ab initio total-energy calculations within the density functional theory(DFT)56using the plane-wave method and the pseudopotential theory with the Vienna ab initio simulation package(V ASP)57We have used the projector-augmented wave scheme(PAW)58implemented in this package.Ba-sis set,including plane waves up to an energy cutoff of 320eV,were used in order to achieve highly converged results and accurate descriptions of the electronic properties. We have used the generalized gradient approximation(GGA)HIGH-PRESSURE VIBRATIONAL AND OPTICAL STUDY...PHYSICAL REVIEW B84,104112(2011)for the description of the exchange-correlation energy with the PBEsol59exchange-correlation prescription.Dense special k-points sampling for the Brillouin zone(BZ)integration were performed in order to obtain very well-converged energies and forces.At each selected volume,the structures were fully relaxed to their equilibrium conﬁguration through the calculation of the forces on atoms and the stress tensor.In the relaxed equilibrium conﬁguration,the forces on the atoms are less than0.002eV/˚A and the deviation of the stress tensor from a diagonal hydrostatic form is less than1kbar(0.1GPa). Since the calculation of the disordered bcc phase was not possible to do,we have attempted to perform calculations for the bcc-like monoclinic C2/m structure proposed in Ref.34. The application of DFT-based total-energy calculations to the study of semiconductors properties under high pressure has been reviewed in Ref.60,showing that the phase stability, electronic and dynamical properties of compounds under pressure are well describe by DFT.Furthermore,since the calculation of the disordered bcc phase is not possible to do with the V ASP code,we have attempted to perform calculations for the bcc-like mono-clinic C2/m structure proposed in Ref.34.Also,because the thermodynamic-phase transition between two structures occurs when the Gibbs free energy(G)is the same for both phases,we have obtained the Gibbs free energy of the different phases using a quasiharmonic Debye model61that allows obtaining G at room temperature from calculations performed for T=0K in order to discuss the relative stability of the different phases proposed in the present work.In order to fully conﬁrm whether the experimentally mea-sured Raman scattering of the high-pressure phases of Bi2Te3 agree with theoretical estimates for these phases,we have also performed lattice-dynamics calculations of the phonon modes in the R-3m,C2/m,and C2/c phases at the zone center ( point)of the BZ.Our theoretical results enable us to assign the Raman modes observed for the different phases of Bi2Te3. Furthermore,the calculations also provide information about the symmetry of the modes and polarization vectors,which is not readily accessible in the present experiment.Highly converged results on forces are required for the calculation of the dynamical matrix.We use the direct-force constant approach(or supercell method).62Highly converged results on forces are required for the calculation of the dynamical matrix. The construction of the dynamical matrix at the point of the BZ is particularly simple and involves separate calculations of the forces in which aﬁxed displacement from the equilibrium conﬁguration of the atoms within the primitive unit cell is considered.Symmetry aids by reducing the number of such independent displacements,reducing the computational effort in the study of the analyzed structures considered in this work.Diagonalization of the dynamical matrix provides both the frequencies of the normal modes and their polarization vectors.It allows to us to identify the irreducible representation and the character of the phonon’s modes at the point.In this work we provide and discuss the calculated frequencies and pressure coefﬁcients of the Raman-active modes for the three calculated phases of Bi2Te3.The theoretical results obtained for infrared-active modes for the three calculated phases of Bi2Te3are given as supplementary material of this article.63Finally,we want to mention that we have also checked the effect of the SO coupling in the structural stability and the phonon frequencies of the different phases.We have found that the effect of the SO coupling is very small and did not affect our present results(small differences of1–3cm−1in the phonon frequencies at the point)but increased substantially the computer time so that the cost of the computation was very high for the more complex monoclinic high-pressure phases, as already discussed in Ref.34.Therefore,all the theoretical values corresponding to lattice-dynamics calculations in the present paper do not include the SO coupling.In order to test our calculations,we show in Table I the calculated lattice parameters in the different phases of Bi2Te3at different pressures.For the sake of comparison we show in Table I other theoretical calculations and experimental results available.As far as the R-3m phase is concerned,our calculated lattice parameters are in relatively good agreement with experimental values from Refs.6and36.Our calculations with GGA-PBEsol give values which are intermediate between those calculated with GGA-PBE and local density approximation (LDA),as it is generally known.Additionally,we give the calculated lattice parameters of Bi2Te3in the monoclinic C2/m and C2/c structures at7.7and15.5GPa,respectively,for comparison with experimental data.Note that in Table I the a and b lattice parameters of the C2/m and C2/c structures at7.7and15.5GPa are very similar to those reported by Zhu et al.;34however,the c lattice parameter andβangle for monoclinic C2/m and C2/c structures differ from those obtained by Zhu et al.34The reason is the results of our ab initio calculations are given in the standard setting for the monoclinic structures,in contrast with Ref.34,for a better comparison to future experiments since many experimentalists use the standard setting.IV.RESULTS AND DISCUSSIONA.Optical absorption ofα-Bi2Te3under pressureIt is known thatα-Bi2Te3has an indirect forbidden bandgap, E gap,between130and170meV.19,64–66Figure1shows the optical transmittance of ourα-Bi2Te3sample in the mid-IR region at room pressure outside the DAC.The spectrum near the fundamental absorption edge is dominated by large interferences.The large amplitude of the interference fringe pattern in the transparent region is a result of the high value of the refractive index,that is larger than9.42,65,66The sample transmittance and the interference-fringe amplitude decreases at low-photon energy due to the onset of free-carrier absorption and to high energies due to the fundamental absorption edge caused by band-to-band absorption.The absorption coefﬁcient can be accurately determined from the transmittance spectrum only in a small photon energy range between the end of the interference pattern and the photon energy at which the transmitted intensity merges into noise.In this interval the absorption coefﬁcient exhibits an exponential dependence on the photon energy.This prevents a detailed analysis of the absorption edge shape.Consequently,the optical bandgap has been determined byﬁtting a calculated transmittance to the experimental one.We calculate the transmittance by assumingR.VILAPLANA et al.PHYSICAL REVIEW B 84,104112(2011)TABLE I.Calculated (th.)and experimental (exp.)lattice parameters,bulk modulus (B 0),and its derivative (B 0 )of Bi 2Te 3in the R -3m structure at ambient pressure and calculated lattice parameters of Bi 2Te 3in the C 2/m and C 2/c structures at 8.4and 15.5GPa,respectively.a(˚A)b(˚A)c(˚A)β(∞)B 0(GPa)B 0 Ref.α-Bi 2Te 3(0GPa)th.(GGA-PBEsol)4.38029.98241.924.89This work th.(GGA-PBESol)a 4.37530.16741.614.68This workth.(GGA-PBE)4.4531.6349th.(GGA-PBE)a 4.4731.1249th.(LDA)a 4.3630.3847exp.4.38530.4976exp.4.38330.38032.5b 10.1b 3640.9c3.2c β-Bi 2Te 3(8.4GPa)th.(GGA-PBESol)14.8834.0669.12189.7341.254.06This workth.(GGA-PBE)d 14.8654.05617.468148.3934exp.d14.6454.09617.251148.4834γ-Bi 2Te 3(15.5GPa)th.(GGA-PBESol)9.8956.9627.70970.3045.283.57This workth.(GGA-PBE)e 9.9567.14610.415134.8634exp.e10.2336.95510.503136.034a Calculations including the SO coupling.bAt room pressure.cAbove 3.2GPa.dAround 12-12.6GPa.eAround 14-14.4GPa.an absorption coefﬁcient with two termsα(E )=A E 2+Be−E gap −E (1)where the ﬁrst one corresponds to the free-carrier contribution and the second one corresponds to the Urbach tail of the fundamental absorption edge.Equation (1)was used to ﬁt the calculated transmittance spectra to the experimental ones.The dotted line in Fig.1was calculated with Equation (1)by using only A and E gap as ﬁtting parameters,where E gap =159meV at roompressure.FIG.1.(Color online)Experimental transmittance of a 7-μm-thick α-Bi 2Te 3sample at room pressure outside the DAC (solid line).Dotted line indicates the ﬁt of the experimental spectrum.Figure 2shows the Bi 2Te 3transmittance spectrum for several pressures up to 5.5GPa.Above that pressure the signal-to-noise ratio is too low to determine the optical bandgap energy.Figure 3shows the pressure dependence of the optical bandgap of Bi 2Te 3,as determined from the previously described procedure.The pressure coefﬁcient turns out to be −6.4±0.6meV /GPa.This pressure coefﬁcient of the optical bandgap is close to the value we obtained for the pressure dependence of the indirect bandgap from ab initio calculations (−10meV /GPa).From this result it appears that,even if the sample becomes opaque at 5.5GPa,Bi 2Te 3still has a ﬁnite bandgap of some 120meV.FIG.2.(Color online)Experimental transmittance of α-Bi 2Te 3at different pressures up to 5.5.GPa.A shift of the absorption edge to low energies is observed with increasing pressure.HIGH-PRESSURE VIBRATIONAL AND OPTICAL STUDY...PHYSICAL REVIEW B84,104112(2011)FIG.3.(Color online)Pressure dependence of the optical bandgap ofα-Bi2Te3according to reﬂectance(red squares)and to transmittance(black circles)measurements.Sample opacity above5.5GPa seems to be then a result of the free-carrier absorption tail shifting to higher energies as the carrier concentration increases.Consequently,the sample opacity is likely caused by the overlap of the free-carrier absorption tail with the fundamental-absorption tail rather than a real closure of the bandgap.We have to note that our pressure coefﬁcient of the optical bandgap is somewhat smaller in module than the pressure coefﬁcient previously reported for the indirect bandgap:−22meV/GPa19;−12meV/GPa below3GPa;and−60meV/GPa above3GPa.20We have to consider that the estimation of these pressure coefﬁcients in Refs.19and20were indirectly obtained from the pressure dependence of the electrical conductivity and those estimations suffer considerable errors since they assume that the change in resistivity is only due to the change of the indirect bandgap energy,which is not a well-founded assumption in extrinsic degenerate semiconductors.In order to conﬁrm our results on optical absorption we have performed high-pressure reﬂectance measurements in a3-μm-thick sample whose results are shown in Fig.4.The reﬂectance spectrum also exhibits a large interference fringe pattern in the transparency region,with amplitude decreasing to lowand high photon energies.The reﬂectance spectrum at6GPaFIG.4.(Color online)Experimental reﬂectance ofα-Bi2Te3at different pressures.shows that the sample exhibits a clear onset of the fundamental absorption edge at around120meV and also that the free-carrier absorption edge,even if it has shifted to higher energies, has not overlapped the fundamental absorption.Therefore our reﬂectance measurements allow us to conﬁrm the results obtained from absorption measurements.Furthermore,the bandgap pressure coefﬁcient,as determined from the shift of the photon energy at which interferences disappear,agrees with the one determined from the transmission spectra.At 7GPa,a clear change in the reﬂectance occurs,with a large increase of the reﬂectance by80%in the low-energy range.A large reﬂectance minimum(not shown here)appears at some 4000cm−1(500meV),suggesting a phase transition to a metallic phase.The metallic nature of the high-pressure phases is in good agreement with previously reported resistivity measurements.17,21,28–30If the reﬂectance minimum is taken as an estimation of the plasma frequency of the high-pressure phase above7GPa,the carrier concentration would be larger than1021cm−3(assuming the same dielectric constant as in the rhombohedral phase).If the dielectric constant inβphase is much smaller,the carrier concentration should be close to1022cm−3,which is more consistent with the observed superconducting behavior.28–30The shift of the free-carrier absorption tail follows the in-crease of the free-carrier plasma frequency.Then the pressure dependence of the plasma frequency can be estimated from the shift of the photon energy at which the free-carrier absorption tail quenches the interference fringe pattern.Reﬂectance measurements outside the cell show that the plasma frequency at ambient pressure is below50meV,consistently with the hole concentration that is of the order of7·1018cm−3,as measured by Hall effect.At4.3GPa interference fringes are observed down to some60meV(560cm−1).This upper limit to the plasma frequency would correspond to hole concentration of lower than1019cm−3,typical of a degenerate semiconductor.This increase in the hole concentration should result in a Burstein-Moss positive contribution to the optical bandgap, which explains the discrepancy between the experimental and theoretical value of the bandgap pressure coefﬁcient.The bandgap around5GPa is in fact smaller than the measured optical gap.Given the band structure of Bi2Te3,67with six equivalent minima in the valence band,the density of states is very large and the hole concentration per minimum would be only of some1.5×1018cm−3,which would lead to a Burstein-Moss shift of some50meV for a hole effective mass of0.09m0.68Then even taking into account the Burstein-Moss shift,Bi2Te3at5GPa would still be a low-gap semiconductor. In fact this estimation of the Burstein-Moss shift is based on the ambient-pressure electronic structure.At pressures above the ETT transition the density of states in the valence-band maximum is expected to be much larger as the ellipsoids merge into a thoroidal ring,as proposed by Istkevitch et al.69 Consequently,the Burstein-Moss shift above the ETT should be much lower than50meV.Finally,we must note that our analysis of the optical absorption edge in Bi2Te3have not allowed us to detect any change in the pressure dependence of the indirect bandgap around3GPa to conﬁrm the presence of an ETT as observed in other works.20,29,31,32,35,36The very small change in the pressure coefﬁcient of the indirect bandgap seems not toR.VILAPLANA et al.PHYSICAL REVIEW B 84,104112(2011)FIG.5.Experimental Raman spectra of α-Bi 2Te 3at pressures between room pressure and 7.4GPa.be affected by the ETT since there is no change in volume but in volume compressibility,and the change is very subtle to be measured in our transmission or reﬂection spectra in comparison with the drastic effects observed in transport measurements or even in the parameters of the Raman modes (as will be discussed in the next section).B.Raman scattering of α-Bi 2Te 3under pressureThe rhombohedral structure of α-Bi 2Te 3is a centrosym-metric structure that has a primitive cell with one Te atom located in a 3a Wyckoff position and the remaining Bi(2)and Te(2)atoms occupying 6c Wyckoff sites.Therefore,group theory allows 10zone-center modes,which decompose in the irreducible representations as follows 70:10=2A 1g +3A 2u +2E g +3E u .(2)The two acoustic branches come from one A 2u and a doubly degenerated E u mode,while the rest correspond to optic modes.Gerade (g)modes are Raman active while ungerade (u)modes are infrared (IR)active.Therefore,there are four Raman-active modes (2A 1g +2E g )and four IR-active modes (2A 2u +2E u ).The E g modes correspond to atomic vibrations in the plane of the layers,while the A 1g modes correspond to vibrations along the c axis perpendicular to the layers.42–44,50Figure 5shows the experimental Raman spectra of α-Bi 2Te 3at different pressures up to 7.4GPa.We have observed and followed under pressure three out of the four Raman-active modes.The E g mode calculated to be close to 40cm −1has not been observed in our experiments as it was also not seen in previous Raman-scattering measurements at room and high pressures.42,50,71–73Figure 6(a)shows the experimental-pressure dependence of the frequencies of the three ﬁrst-orderRaman modes measured in α-Bi 2Te 3,and Table II summarizes our experimental and theoretical ﬁrst-order Raman-mode frequencies and pressure coefﬁcients in the rhombohedral phase.Our experimental frequencies at room pressure are in good agreement with those already measured in Ref.42and Ref.50and with those recently measured in Refs.45and 71–73.On the other hand our theoretical frequencies at room pressure are also in good agreement with those reported in Ref.49without SO coupling (see Table II )and are slightly larger than those calculated including SO coupling (see Ref.49).In Fig.6(a)it can be observed that all the measured Raman modes exhibit a hardening with increasing pressure.The experimental values of the pressure coefﬁcients of the Raman-mode frequencies are in a general good agreement with our theoretical calculations and with the values reported in Ref.50up to 0.5GPa;however,a decrease of the pressure coefﬁcient of two modes around 4.0GPa should be noted [see dashed lines in Fig.6(b)].We have attributed the less positive pressure coefﬁcient of these two Raman modes to the pressure-induced ETT observed in Sb 2Te 3and Bi 2Te 3.20,29,31,32,35,36In fact in a previous study in Sb 2Te 3under pressure we have found a change in the pressure coefﬁcient of the frequency of all modes measured.51In order to support our hypothesis we also plot as Fig.6(b)the pressure dependence of the full width at half maximum (FWHM)of the three measured Raman modes.Curiously,it is observed that the FWHM changes its slope around 4GPa thus conﬁrming an anomaly related to the ETT.Therefore,both our results of the pressure dependence of the frequency and linewidth give support to the observation of the ETT around 4.0GPa in α-Bi 2Te 3similarly to the case of α-Sb 2Te 3.51As previously commented,anomalies in the phonon spec-trum are also expected for materials undergoing a ETT and have been observed in Sb 1.5Bi 0.5Te 3.15In the latter work the high-frequency A 1g mode was not altered near the ETT in good agreement with our measurements;however,we have noted a change both in the lower A 1g and the higher-frequency E g modes.Since A 1g modes are polarized in the direction perpendicular to the layers while the E g modes are polarized along the layers,our observation of a less positive pressure coefﬁcient at 4.0GPa of both modes in α-Bi 2Te 3suggests that the ETT in Bi 2Te 3is related to a change of the structural compressibility of both the direction perpendicular to the layers and the direction along the layers.This seems not to be in agreement with Polian et al.’s observations,which suggest that the ETT in Bi 2Te 3only affects the plane of the layers.36Consequently,more work is needed to understand the mechanism of the ETT in this material.To conclude this section regarding the rhombohedral structure of α-Bi 2Te 3,we want to make a comment on the pressure coefﬁcients of the Raman modes of this structure in comparison to those recently measured in α-Sb 2Te 3.51It is known that in chalcogenide laminar materials,the two lowest frequency E and A modes are usually related to shear vibrations between adjacent layers along the a -b plane and to vibrations of one layer against the others along the c axis,respectively.It has been commented that the E mode displays the smallest pressure coefﬁcient due to the weak bending force constant between the interlayer distances (in our case,Te-Te distances)while。

碳纳米管聚合物复合材料的导电机理及其性能研究

碳纳米管聚合物复合材料的导电机理及其性能研究碳纳米管（CNT）聚合物复合材料是一种由碳纳米管与聚合物基体相互作用形成的新型材料。

在这种复合材料中，CNT作为导电填料，可通过其独特的电子输运机制提供高导电性能。

在本文中，我们将探讨碳纳米管聚合物复合材料的导电机理及其性能研究。

首先，我们来了解碳纳米管的电子输运机制。

碳纳米管是碳原子形成的管状结构，具有特殊的晶格结构。

这种结构使得电子在碳纳米管中以“量子通道”的形式传输，即只有在特定的能级上电子才能通过。

这种量子限制使得碳纳米管具有优异的导电性能，远远超过传统材料。

其次，我们将讨论碳纳米管与聚合物基体的相互作用。

碳纳米管的高表面积和独特的晶格结构使其能够与聚合物基体形成强力的相互作用。

这包括物理吸附、化学键和静电作用等。

通过这种相互作用，碳纳米管可以均匀分散在聚合物基体中，形成三维导电网络。

在导电机理方面，碳纳米管通过两种方式提供导电性能。

首先，碳纳米管通过与聚合物基体形成的连续网状结构，在复合材料中形成一个导电通道。

这种导电通道可以提供高导电性能，使得复合材料具有良好的导电性能。

其次，碳纳米管还可以通过在体积分数很低的情况下形成的电子传输途径来提供导电性能。

这是由于碳纳米管的高导电性能和导电路径的短距离等特点，使得电子能够快速地从碳纳米管中传输，从而形成良好的导电性能。

在性能研究方面，研究人员着重于探索不同形态的碳纳米管聚合物复合材料，并对其导电性能进行评估。

研究表明，碳纳米管的形态和含量对复合材料的导电性能有重要影响。

例如，采用短碳纳米管可以增加导电性能，因为短碳纳米管可以更好地分散在聚合物基体中，并形成更多的导电通道。

此外，通过控制碳纳米管的含量，可以调控导电性能，具有很大的灵活性。

总之，碳纳米管聚合物复合材料具有良好的导电性能，其导电机理与碳纳米管的特殊结构和与聚合物基体的相互作用密切相关。

通过对碳纳米管的形态和含量进行调控，可以进一步优化复合材料的导电性能。

多壁碳纳米管对聚苯硫醚力学性能的增强效应_蒋震宇

dEc ）在 2.4~64 GPa 范围内变 dV f
化
[4, 28]
dEc 。本研究中，在碳纳米管含量较低时（0.37 dV f
vol%）达到了相当高的水平（~60.5 GPa），然而当碳纳米管含量超过 0.73 vol% 后，逐渐降低至中等水平（~15.8 GPa）。在提高聚苯硫醚纳米复合材料模量和强度的同时，碳纳米管的引入降低了聚苯硫醚的延展性。纳米复合材料的断裂应变随着碳纳米管的含量单调下降，当碳纳米管含量为 5.97 vol% 时，纳米复合材料的断裂应变仅为未填充聚苯硫醚的 54%。该结果反映了碳纳米管对聚合物高分子链运动的约束作用。
第17届全国复合材料学术会议论文
多壁碳纳米管对聚苯硫醚力学性能的增强效应
Reinforcing Effect of Multi-Walled Carbon Nanotubes on the Mechanical Properties of Polyphenylene Sulfide
华南理工大学土木与交通学院 [ 摘要 ] 聚苯硫醚是现今主要的高性能热塑性材料之一，基于聚苯硫醚的高性能复合材料，已逐渐用于航空制造。通过双螺杆挤出技术将多壁碳纳米管分散至聚苯硫醚基体，并对形成的纳米复合材料的力学性能进行了研究。实验表明，多壁碳纳米管能够明显增强聚苯硫醚的模量和强度。基于上述结果，分析了影响多壁碳纳米管对聚苯硫醚增强效应的主要因素，对 Halpin–Tsai 模型进行了修正。修正后的模型经验证可适用于预测基于其它高性能热塑性基体的碳纳米管增强复合材料的力学性能。关键字：碳纳米管聚苯硫醚纳米复合材料力学性能弹性模量 [Abstract] Polyphenylene sulfide (PPS)/multi-walled carbon nanotube (MWCNT) composites were prepared using a melt-blending procedure combining twin-screw extrusion with centrifugal pre-mixing. The mechanical properties of PPS were markedly enhanced by the incorporation of MWCNTs. Halpin-Tsai equations, modified with an efficiency factor, were used to model the elastic properties of the nanocomposites. The theoretically predicted modulus showed good agreement with the experimental results for both PPS and polyetheretherketone (PEEK). Keywords: Carbon nanotubes Polyphenylene sulfide Nanocomposites Mechanical properties Elastic modulus 蒋震宇黄健彰

碳纳米管增强金属基复合材料的研究进展

碳纳米管增强金属基复合材料的研究进展何天兵;胡仁伟;何晓磊;李沛勇【摘要】Carbon nanotube reinforced metal matrix composites(CNT/MMCs)owing to high specific strength and specific elastic modulus as well as exceptional thermal and electrical properties,possess great potential in aerospace applications.Based on the analysis on the published literatures,the pro-cessing techniques and the CNT/metal interface research advances was evaluated,and some typical properties were summarized.It is pointed out that,the dispersion of carbon nanotubes,and interfacial characteristics between CNT and metal matrix would be mainly important research areas in future.%碳纳米管增强金属基复合材料由于高的比强度、比模量以及优异的热、电性能在航空航天领域具有很好的应用潜力，本文在分析大量文献的基础上，评述该类材料的制备技术和界面研究进展，对其典型性能进行归纳，指出碳纳米管的分散技术以及碳管、基体之间的界面特性应该是今后本领域的重点研究方向。

【期刊名称】《材料工程》【年(卷),期】2015(000)010【总页数】11页(P91-101)【关键词】碳纳米管;金属基复合材料;制备技术;分散性;界面【作者】何天兵;胡仁伟;何晓磊;李沛勇【作者单位】北京航空材料研究院，北京 100095;总参陆航部装备发展办公室，北京 100082;北京航空材料研究院，北京 100095;北京航空材料研究院，北京100095【正文语种】中文【中图分类】TB333航空航天技术的迅速发展对材料的性能提出了越来越高的要求，传统材料已经存在一定的局限性，如铝合金弹性模量低，热膨胀系数大；钛合金热导率低等。

碳纳米管增强复合材料的力学性能研究

碳纳米管增强复合材料的力学性能研究复合材料是由两种或多种不同类型的材料通过一定的加工方式组合在一起而成，其中一种被称为增强相，另一种则称为基质相。

碳纳米管（Carbon Nanotube，简称CNT）作为一种新型的增强相材料，因其出色的力学性能而受到广泛关注。

本文将重点探讨碳纳米管增强复合材料的力学性能，并评估其潜在应用。

1. 碳纳米管的结构与性质碳纳米管是由由一个或多个由碳原子构成的六角截面的圆柱体组成的纳米级管状结构。

碳纳米管具有极高的比强度和比刚度，同时具有优良的导电性和导热性。

这些特性使得碳纳米管成为增强复合材料理想的增强相材料。

2. 碳纳米管增强复合材料的制备方法碳纳米管可以通过化学气相沉积、热解石墨和碳化物等方法制备得到。

在制备碳纳米管增强复合材料时，一般将碳纳米管与基质相材料进行混合，通过化学反应、传统制备方法或纳米级的加工方法使其形成复合材料。

3. 碳纳米管在普通复合材料中的作用由于碳纳米管的高比强度和高比刚度特性，将其引入普通复合材料中可以显著提高材料的力学性能。

碳纳米管的加入可以增加复合材料的强度、刚度和韧性，同时降低其密度。

这些改善的力学性能使得碳纳米管增强复合材料在结构材料、航空航天和汽车工业等领域具有广泛的应用前景。

4. 碳纳米管与基质相的界面碳纳米管与基质相之间的界面是影响复合材料力学性能的关键因素。

良好的界面相互作用可以有效地传递应力，提高复合材料的强度。

一些技术，如化学修饰和表面涂覆处理，已经被应用于改善碳纳米管与基质相之间的界面结合性能。

5. 碳纳米管增强复合材料的力学性能评价方法评价碳纳米管增强复合材料的力学性能通常涉及拉伸、压缩和弯曲等力学测试。

通过这些测试，可以了解复合材料的强度、刚度、韧性和疲劳性能等关键力学指标。

此外，还可以使用纳米力学测试方法研究碳纳米管在复合材料中的局部机械性能。

6. 碳纳米管增强复合材料的应用前景由于碳纳米管增强复合材料的出色力学性能和广泛的应用领域，它已经被广泛研究并应用于结构材料、电子器件、能源存储和传感器等领域。

炭黑、导电炭黑和碳纳米管在天然橡胶中补强性能的对比研究

炭黑、导电炭黑和碳纳米管在天然橡胶中补强性能的对比研究杨绪迎;吕佳萍;裴红兵【摘要】研究了填充各种填料的天然橡胶的性能.使用的填料分别为高耐磨炭黑N330、导电炭黑XE2-B和碳纳米管(CNT),应用了未处理的和经声振处理的碳纳米管(简称分别为U-CNT和S-CNT).填料用量由0份变化到8.0份.研究发现,随着填料用量增大,胶料黏度增大,硫化时间减小,交联密度增大,模量和硬度增大.对于填充N330和XE2-B的胶料,填料用量增大,拉伸强度持续增大.对于填充U-CNT和S-CNT的胶料,在添加量小于2.0份时,拉伸强度随用量增大而增大;大于2.0份后则明显减小.在填料用量相同的情况下,填充碳纳米管的胶料的导电性、导热性、贮能模量和损耗因子的测量值最大,其次分别是XE2-B和N330.试验结果表明,在没有表面活性剂的前提下,对碳纳米管进行声振处理并不能改善其混炼时的分散度,因此,U-CNT和S-CNT填充胶料的性能没有明显区别.【期刊名称】《世界橡胶工业》【年(卷),期】2016(043)001【总页数】6页(P23-28)【关键词】炭黑;导电炭黑;碳纳米管;天然橡胶【作者】杨绪迎;吕佳萍;裴红兵【作者单位】北京橡胶工业研究设计院,北京100143;北京橡胶工业研究设计院,北京100143;北京橡胶工业研究设计院,北京100143【正文语种】中文【中图分类】TQ330.38+3碳纳米管(СNТ)是一种新型材料,其碳原子聚集在一起形成一种圆柱形结构,长径比特别大。

СNТ分为两个主要类别:单壁碳纳米管(SWСNТ)和多壁碳纳米管(МWСNТ)。

МWСNТ是SWСNТ圆柱体的同轴集合体,一个圆柱体含在另一个圆柱体之内。

СNТ引起许多研究人员的注意是源于其具有出色的性能,如特别大的弹性模量和拉伸强度,以及杰出的导热性和导电性。

因此,СNТ在许多行业可作为特殊添加剂使用。

但是,СNТ大的长径比和大的柔韧性增大了其相互纠缠度,导致其在聚合物胶料中分散困难。

碳纳米管复合材料

碳纳米管复合材料碳纳米管是一种由碳原子构成的纳米材料，具有极高的强度和导电性能。

碳纳米管复合材料是将碳纳米管与其他材料结合而成的复合材料，具有优异的性能和广泛的应用前景。

本文将从碳纳米管的特性、制备方法、以及在复合材料中的应用等方面进行介绍。

首先，我们来了解一下碳纳米管的特性。

碳纳米管具有极高的比表面积和机械强度，同时具有优异的导电性和导热性能。

这使得碳纳米管在复合材料中具有很大的优势，可以显著提高复合材料的力学性能和导电性能。

此外，碳纳米管还具有良好的化学稳定性和耐腐蚀性，能够在恶劣的环境下保持稳定的性能。

其次，我们来看一下碳纳米管复合材料的制备方法。

目前，制备碳纳米管复合材料的方法主要包括物理混合法、化学还原法和原位合成法等。

物理混合法是将碳纳米管与其他材料进行机械混合，然后通过热压或注塑等工艺将其制备成复合材料。

化学还原法则是利用化学方法将碳纳米管与其他材料进行还原反应，形成复合材料。

原位合成法则是在制备过程中直接在碳纳米管上合成其他材料，形成复合材料。

这些方法各有优缺点，可以根据具体的应用需求选择合适的方法。

最后，我们来讨论一下碳纳米管复合材料在各个领域的应用。

碳纳米管复合材料在航空航天、汽车制造、电子设备、医疗器械等领域都有着广泛的应用。

在航空航天领域，碳纳米管复合材料可以制备轻质高强度的结构材料，用于制造飞机、卫星等航天器件。

在汽车制造领域，碳纳米管复合材料可以制备高强度、耐磨损的汽车零部件，提高汽车的安全性和耐久性。

在电子设备领域，碳纳米管复合材料可以制备柔性电子材料，用于制造柔性显示屏、柔性电池等产品。

在医疗器械领域，碳纳米管复合材料可以制备生物相容性良好的材料，用于制造人工骨骼、人工关节等医疗器械。

总之，碳纳米管复合材料具有优异的性能和广泛的应用前景，将在未来得到更广泛的应用。

随着制备技术的不断进步和应用领域的不断拓展，碳纳米管复合材料将为人类社会带来更多的惊喜和便利。

PA6／CNT复合材料的动态机械性能和增强机理分析

维普资讯第３卷增源自５２０年６月０７
塑料工业
ＣＮＰＡＨＩＡＬｎＣＵＳＲＹＳＩＮＤ＇Ｔ・２７・４
Ｐ６ＣＴ复合材料的动态机械性能和Ａ／Ｎ增强机理分析桨
孙莉。杨晋涛，施艳琴，钟明强 “
ａｔｒｕｈｖｇｒｕｅｃｏｓａｉｅｅａｕｅｈｇｒｓｕｄｍｅｈｎｃｓｒｉｇｆｃｉｏｏｓｒａｔｎｓｈｇｔｍｐｒｔｒ．ｉｈｐｓｒａｃａｉｔｒ．卟ｅｎｃｅｔｎｅｅｔｏｅｓｉｈｅｅｎｉｎｕｌａｏｆｃｆｉｓｈｓｍａｌａｔｌｏｌｎｒａｅｔｅｒｅｏｒｓｌａｉｔｔｅｅｓｌｒｐｒｃｓｃｕｄｉｃｅｓｅｄｇｅｆｃｙｔｌｚｔｎｏｅｃｍｐｓｔ．Ｏｅｗｓ，ａｄｔｅｉａｒ — ｅｉｅｈａｉｏｆｈｏｏｉｅｈｔｒｉｅｎｎｃｏｈｍｏｅｕｅｃａｎｆＡ６ｗｕｄｒａｔｔｅ— Ｎｄ— ＣＯＨｇｏｐｎｔｅＣＴ。ｗｉｈｍａｅｔｅｓｏａｅｌｌｈｉｓｏｏｅｃｈｔｃＰｌｉｗｈＨ２ｎａＯｒｕｓｏＮｓｈ３ｈｃｄｔｒｇｈｍｅｕｕｎｄｌｓｄｕ，ｏＡｏｏｉｉｅ ’ ｔＮＴｈｇｅａｏｆＰ６ＣＴａｄｄｌｓＥ’ａｏｓｍｏｕｓＥ，Ｐ６ｃｍｐｓｅｌｄｖｈＣｓ３ｌｆｔｓ Ⅱ ｉｉｒｔｎｔｓｏＡ／Ｎｓ１ｎｈｈｈｅＰ／Ｎｃｍｐｓｅ．ＣＴｃｎａｎｄｍｏ — ＣＯＨｔａＮＴ。Ｓｅｓｒｇｄｕ ’ ｄｌｓＡ６ＣＴｓ２ｏｏｉｓＮｓ１ｏｔｉｅｒｔｅＯｎＣｓｈ２ＯｔｔａｅｍｏｕｓＥａｓｈｏｌｎｏ

碳纳米管浓缩物在复合材料中的实际应用

· 36 ·玻璃钢 2011年第2期译文碳纳米管浓缩物在复合材料中的实际应用王强华编译（上海玻璃钢研究院有限公司，上海 201404）摘要碳纳米管可用于增强复合材料并提供导电性。

典型的碳纳米管用量在0.2-1%重量份的范围内，这使它们成为一种具有较高竞争力的添加剂。

由于直接把它们以原始粉末状添加到基体中，需要广泛的专业技术，因此Arkema 公司已开发出多种现成可用的解决方案，它们由含量较高的浓缩物组成。

与市场上提供的碳纳米管含量小于2%的液体分散剂相比，这些浓缩物提高了配制的灵活性，容易使用，同时降低成本。

过去十年中，新的纳米材料技术在能源、光学、电子、材料和医药领域不断兴起。

对纳米材料生产工艺和性能不断的认识，以及该行业致力于开发这些技术，使得纳米技术非常高效地走向成熟。

图1显示在过去二十年里有关碳纳米管出版物的数量。

碳复合材料也被包括在这张图中进行对比。

自2000年以来，对于这两种材料，其出版物的数量呈指数增长。

这种趋势可能就表明了碳以它所有的形式将成为明天技术的基础材料，这是因为它具有较低的重量，非凡的力学和电性能。

碳纳米管的全球产能估计每年2000吨（2011预测）。

碳纳米管用一个和石墨非常相似的碳同素异形体制成。

它们首次在1983年通过Hyperion 催化合成，由石墨层卷起形成封端的圆柱体组成。

对于多层碳纳米管（MWCNT ），几个圆柱体（一般5到10个）被组装在一起形成类似俄罗斯卷条的结构（图2d ）。

多层碳纳米管直径10-15nm ，图1 在过去20年中每年的出版物数量碳复合材料碳纳米管每年出版物数量长度有几个微米。

图2 Arkema公司多层碳纳米管的SEM（a-b）和TEM（c-d）照片，它们还未和基体混合，形成Graphistrength®浓缩物1Graphistrength®多层碳纳米管（MWCNTs）的高效使用对于大多数应用，多层碳纳米管在基体中的分散情况是从其优异性能中获益的关键。