Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Physics

Major Professor

George S. Nolas, Ph.D.

Committee Member

Jacob Gayles, Ph.D.

Committee Member

Dmitri Voronine, Ph.D.

Committee Member

Michael C. Wang, Ph.D.

Keywords

lattice disorder, photovoltaics, Quaternary chalcogenides, thermoelectrics

Abstract

Inorganic materials with unique physical properties are vital components of modern technology, from electronic devices to energy storage and conversion systems. Recent advancements in materials research and development have garnered significant interest, particularly in the realm of sustainable energy applications like thermoelectrics and photovoltaics. The development of novel materials with enhanced electronic and thermal properties has emerged as a focal point in advancing these critical applications. Furthermore, low thermal conductivity materials are sought after for technologically significant applications such as thermal barrier coatings, rewriteable data storage utilizing phase change materials and thermoelectrics. However, the current efficiency levels of materials used in devices for these applications remain relatively low, thereby underscoring the imperative for continued research and development efforts. Multinary metal chalcogenides consisting of many possible compositions constitute potential candidates in the development of future high-performance materials for applications of interest. The purpose of this work is to expand the current knowledge of the structural, chemical, and physical properties of quaternary metal chalcogenide materials, as well as advance our understanding of their structure-property relationships, while simultaneously exploring novel compositions and synthetic pathways to obtain these materials in phase pure form.

Quaternary metal chalcogenide materials are receiving attention for their unique properties that stem from compositional and structural variation that give rise to significant implications for the properties of these materials, as well as the fact that they can be manipulated to exhibit diverse physical properties. Recent studies have shown that they may hold a promise for the development of materials with enhanced and tailored properties for advancing technological innovations. For example, kesterites have strong absorption in the visible, as well as exhibit high thermoelectric power factor and low thermal conductivity, properties that are of interest for optoelectronic and thermoelectric applications, respectively. The discovery of novel quaternary chalcogenides and an understanding of their structure-property relationships are paramount and have a major role to play in the development of future high-performance chalcogenide materials. Moreover, disorder-driven transport in crystalline materials is a field of growing interest as lattice defects can have a great effect on the transport properties of materials, which can be realized in quaternary chalcogenides. The central hypothesis is that by inherent or introduced lattice defects and disorder in the crystal structure the electronic and thermal properties can be significantly altered, leading to distinct and unique physical properties of interest.

In this dissertation I will discuss my investigations of the I-II2-III-VI4 and I-III-IV-VI4 quaternary chalcogenide families of compounds (where I = Cu or Ag; II = Zn or Cd; III = Al, Ga or In; VI = Ge or Sn; and VI = S, Se or Te), which primarily consist of low-cost, earth-abundant and non-toxic constituent elements. In addition, I will describe their structure-property relationships, potential applications, as well as scientific challenges they present. These quaternary chalcogenides can be thought of as derivatives of simpler II-VI binary compounds obtained via cation cross substitution. The materials form in a cubic disordered zinc-blende, cubic disordered-spinel or tetragonal defect-chalcopyrite structure, with physical properties that are of interest for technologically significant applications. In addition, the complex quaternary chalcogenides, PbCuBiS3 and Ba3Cu2Sn3Se10, prepared by ball milling and solid-state annealing techniques, were investigated. Their structural, temperature-dependent thermal properties and the mechanisms of their ultralow thermal conductivity were revealed and elucidated. This investigation advances our understanding of quaternary chalcogenides and helps assess their suitability for various applications.

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