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 对于 Zintl 相（具有后过渡元素的正电性金属的价化合物：涉及两中心双电子键的共价网络和笼）和 Hume-Rothery 相（后期和后过渡的金属间化合物），价电子浓度（vec = 电子/原子比）对结构的影响作用已有详细记录。 元素：涉及“金属”键的致密堆积）。 Zintl 相发生在 vec 4 上（基于转变后元素的网络），而 Hume-Rothery 相则在 vec ~ 2 上观察到。迄今为止，还没有对 vec 中这两个极端之间的广泛区域进行系统研究。由于两个已建立的化合物类别在结构原理和电子特性方面表现出巨大差异，因此涉及中间状态下 vec 的化合物的研究将提供一种检查从一类到另一类的转变的方法。 这项研究涉及三元化合物的合成和详细表征，其中涉及（i）带正电的碱土金属或稀土金属； (ii) 后过渡金属，即第 8-12 族元素或 Li 或 Mg 之一； (iii) 13 族元素（Al、Ga、In），称为“trielides”，以便通过调整电子计数来探测 vec 在 2 到 4 之间的材料。合成策略将包括高温方法（电弧熔化）和使用金属助熔剂。将检查产品的晶体结构、成分和物理特性。特别是，将利用 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将硼、碳和氮掺入这些金属间化合物中。除了这些实验方法之外，还将应用理论方法来研究这些 e 系统中 vec 变化时的价电子分布。具体来说，将探索这些固体和分子类似物之间的关系，例如从金属碳硼烷三角面体到 Zintl 型阴离子笼。半经验电子结构计算将用于检查所研究的三元系统，希望使 LMTO 计算适应这些复杂系统。 %%% 这项研究代表了实验和理论的首次共同努力，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系统检查。本研究中的三元化合物可能表现出高电导率以及强共价键合区域。因此，这些材料可以作为高温金属提供潜在的应用，或者可以提供研究金属间化合物的强化或脆化机制的方法。