Combinatorial approach to materials synthesis: Using the hydride method in conjunction with in-situ studies and theoretical calculations
Date
2022-12
Authors
Cox, Tori
Major Professor
Advisor
Zaikina, Julia V
Miller, Gordon J
Pecharsky, Vitalij K
Windus, Theresa L
Kovnir, Kirill
Committee Member
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Abstract
Traditional synthesis of alkali-metal-containing antimonides is a major hurdle to discovery of new compounds within ternary alkali metal and antimony-containing systems. Traditional synthetic methods require the diffusion of the alkali metal throughout the sample which often reacts in the early stages of synthesis to form alkali metal-rich binary or ternary phases. To further react these phases, high temperatures, long dwelling durations, and multiple re-grindings and re-annealings must be employed. This oftentimes results in thermodynamically stable products thereby bypassing potentially metastable phases in the system.
In my dissertation, a synthetic technique utilizing alkali metal hydride precursors is employed along with formation energy prediction to target compositions of prospective new materials rapidly and precisely. After scanning compositional phase space with the hydride method, discovered ternary phases are then analyzed using in-situ high-temperature diffraction methods to determine their thermal stability as well as scan for potential high-temperature polymorphs. Utilizing such an approach, six new compounds with new crystal structures have been synthesized: K8-xZn18+3xSb16, K58Zn122Sb207, m-K4Cd6Sb8, t-K3Cd11Sb8, h-K3Cd17Sb14, and c-K3Cd12Sb10. A similar process utilizing formation energy prediction and the hydride method was then employed for bismuthides resulting in the discovery of KZnBi, KCdBi, KZn2Bi2, and KCd2Bi2. Upon discovery, each new compound’s transport or magnetic properties were characterized, and their crystal structures were solved.
Overall, this work emphasizes the efficacy of coupling formation energy prediction to narrow the compositional region that is further experimentally screened with the rapid hydride synthesis method, while in-situ studies determine thermal stability and other possible high-temperature polymorphs therefore providing a fast and efficient way of investigating underexplored phase space. It also introduces a variety of new antimonide and bismuthide crystal structures and the resultant physical properties to the solid-state and materials chemist community.
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Type
dissertation