Structure-Composition-Property Relationships in Complex Intermetallic Phases: Experimental Studies and Theoretical Predictions

本项目涉及新的多元化合物的合成和详细表征，所述新的多元化合物包括（i）正电性碱金属、碱土金属或稀土金属;（ii）来自后过渡金属族的过渡金属，即Mn-Zn族;和（iii）“较轻”的第13或14族元素，特别是Al、Ga、Si和Ge。 由于活性金属（i）和过渡/后过渡金属（ii）和（iii）之间的电负性的显著差异，这类化合物可以被称为“极性金属间化合物”。 选择第13族和第14族元素是因为它们在元素周期表中的位置处于金属和非金属之间的边界。 这些元素的组合有望创造出美丽的复杂结构，包括相互连接的层或相互渗透的原子簇，这将允许彻底研究组成，结构，性质和化学键之间的关系。 考虑到第13和14族元素与非金属的接近性，我们预计它们的结构将受到化学键和电子结构的强烈影响。 此外，还可以研究从金属到半金属的过渡，然后半导体行为，以及当掺入稀土元素时不寻常的价态行为。 这个项目的继续发展探索f-d-p和f-p系统，其中价4f态接近d-p或p元素框架中成键和反键态之间的过渡。 电子结构的这一特征为有趣的热、磁和电行为创造了可能性。 该项目的另一个方面是使用第一性原理电子结构计算来研究尚未观察到的三元组成，但与已发现的化学系统是等电子的，和其他“不存在的”极性金属间相，以获得关于金属间化合物形成的驱动力的基本信息。技术概述该研究仍然是在单个研究小组内进行实验和理论的首次协同努力之一，以系统地寻找具有潜在感兴趣的物理或化学性质的新的金属间化合物，例如热电体、超导体或新型磁性材料。该策略涉及“修补”电子结构，即，富金属化合物中的化学键，以引起电子、磁性和热响应的变化。 通过将实验与最先进的理论计算相结合，可能会出现一些预测能力，并允许专门定制新的金属间化合物。 该项目的成果将被纳入物理科学本科生和研究生的在线教育资源，并将成为致力于固态化学进步的教科书的组成部分。 与德国德累斯顿和慕尼黑的小组正在进行的合作将继续发展，相互作用将加强这一努力的理论和实验方面。

TECHNICAL SUMMARYThis project involves the synthesis and detailed characterization of new multinary compounds involving (i) an electropositive alkali, alkaline earth, or rare earth metal; (ii) a transition metal from the later transition metal groups, viz, Mn-Zn groups; and (iii) a "lighter" group 13 or 14 element, in particular, Al, Ga, Si, and Ge. This class of compounds can be called 'polar intermetallics' due to the significant differences in electronegativities between the active metals (i) and the transition/post-transition metals (ii) and (iii). The group 13 and 14 elements are selected because their position in the Periodic Table of Elements is at the border between metals and nonmetals. These combinations of elements are anticipated to create beautifully complex structures involving interconnected layers or interpenetrating clusters of atoms that will allow a thorough investigation of the relationships among composition, structure, properties, and chemical bonding. Given the proximity of the group 13 and 14 elements to nonmetals, we anticipate their structures will be strongly influenced by chemical bonding and electronic structure. Furthermore, the transition from metallic to semimetallic and then semiconducting behavior may also be studied, as well as unusual valence state behavior when rare-earth elements are incorporated. Continuing developments of this project explore f-d-p and f-p systems in which valence 4f states fall close to the transition between bonding and antibonding states in the d-p or p-element framework. This feature of the electronic structure creates the possibility for interesting thermal, magnetic, and electrical behavior. An additional aspect of the project is to use first principles electronic structure calculations to study ternary compositions that have not been yet observed, but are isoelectronic with chemical systems that have been discovered, and other "nonexistent" polar intermetallic phases to obtain fundamental information about the driving forces for intermetallic compound formation.NON-TECHNICAL SUMMARYThis investigation continues to be one of the first concerted efforts of both experiment and theory within a single research group to search systematically for new intermetallic compounds with potentially interesting physical or chemical properties, such as thermoelectrics, superconductors, or novel magnetic materials. The strategy involves "tinkering' with the electronic structure, i.e., the chemical bonding in metal-rich compounds to induce changes in electronic, magnetic, and thermal responses. By coupling experiment with state-of-the-art theoretical calculations, some predictive capabilities may emerge and allow new intermetallics to be specifically tailored. Outcomes of this project will be incorporated into on-line educational resources for undergraduate and graduate students in the physical sciences, and will be components of a textbook dedicated to advances in solid-state chemistry. On-going collaborations with groups in Dresden and Munich, Germany will continue to be developed, interactions that will enhance both the theoretical and experimental aspects of this effort.