## Engineering and Applied Science Theses & Dissertations

#### Title

Toward Improved Computational Tools for Electronic Transport Analysis and their use in the Development of Materials for Energy Applications

#### Date of Award

Winter 12-15-2014

#### Author's School

School of Engineering & Applied Science

#### Author's Department

Energy, Environmental & Chemical Engineering

#### Degree Name

Doctor of Philosophy (PhD)

Dissertation

#### Abstract

With the rapid rise in computational speed and capacity of massively parallel computing clusters in recent years, theoretical screening of large, previously unexplored sets of complex compounds to find materials with a given set of desired properties is quickly becoming a reality. In order to maximize the predictive ability of these large-scale computations, it is desirable to develop accurate post-processing algorithms that can efficiently manipulate electronic structure data to produce theoretical predictions of experimentally observable quantities. To address this need, the work of this dissertation has been to expand existing \textit{ab initio} methods for determining electronic properties of bulk complex structures to allow for the characterization of both n- and p-type semiconducting materials. Although previous methods have successfully characterized carrier transport in n-type materials which obey the spherical parabolic band approximation, these methods have failed for p-type materials for which band warping results in asymmetry of carrier transport. As part of this work, we develop a generic algorithm for determining the curvature of semiconductor bands near the band edge, and use the results to process band data and derive electronic properties such as effective masses, electronic conductivity, and Seebeck coefficient. To illustrate the flexibility and utility of the methods developed, we apply them to a variety of bulk systems and show how such analysis can help not only to identify potentially successful materials, but also to gain insight into the relationship between electronic structure and material properties. Specifically, we study metallic atom filled skutterudites and their electronic properties in context of thermoelectric theory and gain knowledge about a secondary electronic structure that forms a resonance lattice within the skutterudite lattice that leads to enhanced electronic conductivities. We also study a new group of potentially transparent conducting oxide spinels and quantify the improvement of electronic properties that results from enahnced valence band curvature. We also introduce the effective mass wheel, and use this technique to visualize deviation from spherical parabolicity for the valence bands of compounds of increasing levels of complexity: Si, GaAs, Cu$_2$O, and a ternary spinel oxide. Lastly, we present an extension to the work performed here through the reformulation of the effective mass problem in a more widely applicable form. We hope that this work helps to advance the ability of materials screening in identifying potentially successful materials for a variety of applications in electronic materials science and solid state energy technologies.

English (en)

John Gleaves

#### Committee Members

Gregory C DeAngelis, Li Yang, Palghat Ramachandran, John Fortner