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

价电子浓度（vec =电子/原子比）对Zintl相（带过渡后元素的正电金属的价化合物：共价网络和包含双中心双电子键的笼）和Hume-Rothery相（晚期和后过渡元素的金属间化合物：包含“金属”键的致密填料）结构的影响已被充分记录。在vec ~ 4中出现Zintl相（基于过渡后元素的网络），在vec ~ 2中观察到Hume-Rothery相。迄今为止，还没有对这两个极端之间的广阔区域进行系统的调查。由于这两类已建立的化合物在结构原理和电子性质上表现出巨大的差异，因此涉及中间态vec化合物的研究将提供一种检查从一类到另一类转变的方法。本研究涉及三元化合物的合成和详细表征，包括：(1)正电碱性土或稀土金属；（ii）晚过渡金属，即8-12族元素或Li或Mg中的一种；（iii）第13族元素（Al, Ga, In），称为“三elides”，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（电弧熔炼）和使用金属助熔剂。将检查产品的晶体结构、成分和物理性质。特别是，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将被利用。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。除了这些实验方法外，理论方法将应用于研究这些电子系统中价电子随vec变化的分布。具体来说，这些固体和分子类似物之间的关系，例如，从金属碳硼烷δ面体到锌型阴离子笼，将被探索。半经验电子结构计算将用于检查所研究的三元系统，并期望使LMTO计算适应这些复杂的系统。这项研究代表了实验和理论的第一次协调一致的努力，对连接络合金属间化合物和络合价化合物的化合物进行了系统的研究。在这项研究中，三元化合物可能表现出高导电性，并伴有强共价键的区域。因此，这些材料可以作为高温金属提供潜在的应用，或者可以为研究金属间化合物的强化或脆化机制提供一种手段。

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.