Condensed-Matter Physics & Materials Science Seminar

The thermoelectric properties of half-Heusler alloys and layered boride intermetallics were measured to 1100 K with the intent of indirectly studying features of their electronic structures and gauging not only their suitability but that of related alloys for high temperature thermoelectric power generation. For the half-Heusler alloys, both transition metal sites were doped in order to study the resultant modifications to the electronic structure near the Fermi energy, which will be discussed in terms of first principles electronic structure calculations. In the case of the layered boride alloys, on the other hand, few electronic calculations have been published, prompting the generalization of a molecular electron counting rule to predict the trends in the densities of states of deltahedral crystalline solids. As a result of the procedure developed for synthesis of boron-rich intermetallics and the improved understanding of bonding trends, layered borides of several previously overlooked structure-types were synthesized and screened for superconductivity, and MoB4 was discovered to be superconducting at 6 to 8 K when doped with Nb or Ti. Structural measurements indicated opposite trends in lattice modification of doped MoB4 than those reported for the superconducting transition metal diborides.