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Defects, dopants, and disorder in thermoelectric materials
Meschke, Vanessa
Meschke, Vanessa
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2024
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Abstract
Modern materials science is driven by the discovery of materials with unique properties, impacting areas from renewable energy to quantum computing.
A crucial aspect of harnessing these findings is explaining the mechanisms behind the properties for replicating findings across various chemistries and structures.
However, due the high dimensional nature of materials science, characterized by an astonishing number of tunable synthetic parameters, this task can be Herculean.
Fortunately, joint efforts in computation and experimentation make it easier to identify and understand these remarkable properties, shifting materials science from empirically driven investigations to targeted investigations informed by deeper insights into unique phenomena.
In this work, we investigate how the synergy between computation and experiment can be used to better understand synthesis-property relationships in AgInTe$_2$ and CuInTe$_2$ and synthesis-structure relationships in Mn$_{1-x}$Ge$_{x}$Te and Sn$_{1-x}$Ge$_{x}$Te alloys.
The first two chapters of this thesis present studies of defects in chalcopyrite-structured AgInTe$_2$ and CuInTe$_2$.
In both cases, we demonstrate the use of phase boundary mapping to experimentally pin the chemical potential, relating synthesis to equilibrium conditions used in first-principles calculations of defect energetics.
For AgInTe$_2$, we successfully predict a complete change of dominant carrier type and effectively introduce dopants into computationally predicted promising regions.
For CuInTe$_2$, we incorporate additional complexity to defect energetics by investigating the behavior of solid solution dopants beyond the dilute limit, demonstrating how the computational and experimental techniques must be combined to employ effective analysis of doped electronic properties.
The second two chapters focus on investigations of local disorder and distortions in Sn$_{1-x}$Ge$_{x}$Te and Mn$_{1-x}$Ge$_x$Te pseudobinary alloys.
To describe these disordered, distorted structures, we employ Boltzmann statistics to create ensemble averages of the pair distribution function (PDF).
The ensembles allow for modeling of tuned degrees of disorder and distortion, allowing for an energy- and synthesis-informed structural model that accurately describes the local structure of these alloys.
For Mn$_{1-x}$Ge$_x$Te, we present this analysis for static disorder, while our work on Sn$_{1-x}$Ge$_{x}$Te demonstrates the incorporation of lattice dynamics on local structure.
Overall, this work demonstrates the need for combining computations and experiment for the targeted design of semiconductor materials, where control over defect energetics and disorder is crucial for savvy design of material properties.
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