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

摘要 DMR-9627161 米勒 价电子浓度（vec =电子/原子比）对影响结构的作用在Zintl相（正电性金属与后过渡元素的价化合物：涉及双中心双电子键的共价网络和笼）和Hume-Rothery相（后过渡元素的金属间化合物：涉及“金属”键的致密堆积）中得到了很好的证明。Vec 4出现Zintl相（基于后过渡元素的网络），Vec ~ 2观察到Hume-Rothery相。到目前为止，还没有系统的调查，在这两个极端之间的广泛地区的vec。由于这两个已建立的化合物类显示出显着的差异，在结构原理和电子性质，研究涉及化合物与vec在中间政权将提供一种手段，检查从一类到另一类的转换。 本研究涉及三元化合物的合成和详细表征，所述三元化合物包括（i）正电性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中的一种，（iii）后过渡金属，即第8-12族元素或Li或Mg中的一种。和（iii）第13族元素（Al、Ga、In），称为“三烯化物”，以便通过调整电子计数来探测具有2和4之间的vec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。将对产品的晶体结构、成分和物理性能进行检查。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。本研究的后期阶段将涉及将硼、碳和氮结合到这些金属间化合物中。除了这些实验方法外，我们还将应用理论方法来研究这些体系中价电子分布随vec的变化。具体而言，这些固体和分子类似物之间的关系，例如，范围从三硼烷三角形到Zintl型阴离子笼。半经验的电子结构计算将被用来检查研究中的三元系统，与适应这些复杂的系统的LMTO计算的愿望。 本研究是第一次将实验和理论结合起来，对复杂金属间化合物与复杂化合物进行系统的研究。本研究中的三元化合物可能显示出与强共价键结合的高电导率。因此，这些材料可以提供潜在的应用，作为高温金属，或可以提供一种手段，研究金属间化合物的强化或脆化机制。

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.