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

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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.