Linking Intermetallics and Zintl Phases: Experimental and Theoretical Studies of Ternary "Trielides"

连接金属间化合物和 Zintl 相：三元“Trielides”的实验和理论研究

• 批准号: 9627161
• 负责人: Gordon Miller
• 金额: $ 30万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-12-01 至 2000-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9627161&HistoricalAwards=false
• 关键词: Linking; Intermetallics; Zintl; Phases; Experimental

Abstract DMR-9627161 Miller The role of valence electron concentration (vec = electron/atom ratio) to influence structure is well documented for Zintl phases (valence compounds of electropositive metals with post-transition elements: covalent networks and cages involving two-center two-electron bonds) and Hume-Rothery phases (intermetallic compounds of late and post-transition elements: dense packings involving "metallic" bonds). Zintl phases occur for vec 4 (based upon the network of post-transition elements) and Hume-Rothery phases are observed for vec ~ 2. To date, there is no systematic investigation of the broad region in vec between these two extremes. Since the two established compound classes show dramatic differences in structural principles and electronic properties, studies involving compounds with vec in the intermediate regime will provide a means of examining the transformation from one class to the other. This research involves the synthesis and detailed characterization of ternary compounds in- volving (i) an electropositive alkaline earth or rare earth metal; (ii) either a late transition metal, i.e. groups 8-12 elements or one of either Li or Mg; and (iii) a group 13 element (Al, Ga, In), called "trielides," in order to probe materials with vec between two and four by tuning the electron count. Synthetic strategies will include high temperature methods (arc-melting) and using metallic fluxes. Products will be examined for their crystal structure, composition, and physical properties. In particular, X-ray and neutron diffraction, electron microscopy, thermal analysis, X-ray photoelectron spectroscopy, electrical resistivity, and magnetic susceptibility measurements will be utilized. Later stages of this investigation will involve the incorporation of boron, carbon, and nitrogen into these intermetallics. In addition to these experimental approaches, theoretical methods will be applied to investigate the valence electron distribution in thes e systems as the vec changes. Specifically, relationships between these solids and molecular analogues, e.g., ranging from metallocarborane deltahedra to Zintl-type anionic cages, will be explored. Semiempirical electronic structure calculations will be used to examine the ternary systems under study, with the aspirations of adapting the LMTO calculations to these complex systems. %%% This investigation represents the first concerted effort of experiment and theory to perform a systematic examination of compounds linking complex intermetallics with complex valence compounds. The ternary compounds in this investigation may show high electrical conductivities coupled with regions of strong covalent bonding. Therefore, these materials may offer potential applications as high temperature metals, or may provide a means of studying either strengthening or embrittlement mechanisms in intermetallics.

摘要dmr-9627161 Miller价电子浓度(vec=电子/原子比)对锌相(含过渡后元素的电正性金属的价态化合物：含双中心两电子键的共价网络和笼子)和休谟-罗瑟相(过渡后期和过渡后元素的金属间化合物：含“金属”键的致密堆积)的影响已有很好的文献记载。VEC 4(基于过渡后元素网络)存在Zintl相，Vc~2存在Hume-Rothery相。到目前为止，还没有对这两个极端之间的Vc的广泛区域进行系统的研究。由于两个已建立的化合物类在结构原理和电子性质上表现出巨大的差异，涉及中间区域中含有Vc的化合物的研究将提供一种检查从一个类到另一个类的转化的方法。这项研究涉及三元化合物的合成和详细表征，这些化合物涉及(I)正电碱土或稀土金属；(Ii)后过渡金属，即第8-12族元素或Li或Mg中的一种；以及(Iii)第13族元素(Al，Ga，In)，称为“Trielide”，以便通过调节电子计数来探测vec在2到4之间的材料。合成战略将包括高温方法(电弧法)和使用金属助熔剂。将对产品的晶体结构、组成和物理性能进行检查。特别是，将使用X射线和中子衍射、电子显微镜、热分析、X射线光电子能谱、电阻率和磁化率测量。这项研究的后期阶段将涉及在这些金属间化合物中加入硼、碳和氮。除了这些实验方法外，还将应用理论方法来研究价电子在VEC变化时在这些体系中的分布。具体地说，将探索这些固体与分子类似物之间的关系，例如从金属碳硼烷三角面体到锌型阴离子笼子。半经验电子结构计算将被用来考察所研究的三元体系，希望使LMTO计算适用于这些复杂的体系。这项研究代表了第一次实验和理论的协同努力，对连接复杂金属间化合物和复杂价态化合物的化合物进行了系统的检查。本研究中的三元化合物可能表现出高电导率和强共价键的区域。因此，这些材料可能作为高温金属具有潜在的应用前景，也可能为研究金属间化合物的强化或脆化机制提供一种手段。