Electrical and thermal transport in quasicrystalline systems.

摘要

Quasicrystals, or quasiperiodic crystals, are materials displaying long-range positional order without short-range rotational symmetry. Atoms within these materials are arranged non-periodically resulting in structural order on only a short-range scale, differing from a truly amorphous material. Due to values for electrical resistivity comparable to other thermoelectric materials and inherently low thermal conductivity, we have begun to investigate the electrical and thermal transport of these materials in order to evaluate their potential as a thermoelectric material.; Due to the large variability of transport properties in quasicrystals resulting from small changes in growth conditions, many different quasicrystals of similar compositions were investigated. A single-phase quasicrystal of Al_70.8Pd_20.9Mn_8.3 was determined to have a thermopower of +85μV/K at 300K, the highest thermopower reported in the AlPdMn quasicrystalline system. Thermopower in this system increased to a value of +120μV/K at 550K, making quasicrystals possible materials for high temperature thermoelectric applications.; In this dissertation, a broad database of thermal and electrical transport properties is assembled. An empirical method for modeling the thermopower in AlPdMn quasicrystals is proposed. From the components of this model one can determine some basic mechanisms governing thermopower in this quasicrystalline system.; A section of this dissertation deals with the transport properties and unusual linear thermal conductivity observed in the stable binary Cd _5.7Yb quasicrystals. The linearity of the thermal conductivity implies no presence of a lattice contribution with the total thermal conductivity composed solely of an electronic contribution, which is in strong contradiction with the Wiedemann-Franz Relationship.; A comprehensive evaluation of electrical and thermal transport reveals many novel materials properties and much interesting physical phenomena.