Paving a Path towards Rational Design of Semiconductor Materials: Exploratory and In Situ Synthesis of Chalcogenides

McClain, Rebecca

doi:https://doi.org/10.21985/n2-rq7z-wz66

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Paving a Path towards Rational Design of Semiconductor Materials: Exploratory and In Situ Synthesis of Chalcogenides

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As the interest in rational synthesis for solid-state materials accelerates, there is an urgent need to understand the design principles concealed within these reactions. In situ material synthesis provides such an avenue to not only uncover these assembling rules, but also for finding new materials even in seemingly familiar phase spaces. Historically, this technique was largely employed for crystallization observations. However, as described in this dissertation, the increased accessibility of in-house diffractometer setups – and consequent decreased requirement for synchrotron or spallation sources – enabled the application of this powerful technique to the chalcogenide and heteroanionic systems. As detailed in the first chapters, all in situ material synthesis measurements yield novel information that build toward an overall understanding of the driving force for reaction progressions and assembly rules. The in situ investigations of the KBiQ2 (Q = S, Se) and BiOCuSe reactions highlight the power of panoramic synthesis to uncover new phases in a well-known system, while tuning precursor ratios, and to unveil a structural intermediate that underlies the formation of the compounds in the A-Pn-Q (A = alkali metal; Pn = Sb, Bi) compositional space. The study of the Bi2O2Se + Cu2Se versus Bi2O3 + Bi + 3 Cu + 3 Se reaction pathways to form BiOCuSe underscores the influence the selection of precursors has on the reaction progression and establishes an understanding of the effects of the chosen precursors. As heteroanionic materials are further investigated, six new materials are discovered. The four novel heteroanionic materials, In8S3-xTe6+x(Te2)3 (x = 0.18), Ba2SnS1.2Te2.8, Ba3SnS4Te, and Ba3SnS5.62Te0.13 are comprised of S2-, Te2-, S22- and/or Te22- with their crystallographically distinct sites. Two solid solutions Ba7Sn5S15-xTex and Ba8Sn4S15-yTey¬ (x = 0.7, y = 0.76) are also discovered in these investigations. The advances in in situ PXRD as well as interrogations into novel compositional spaces, point the way towards more wide-ranging studies to fully flesh out the design principles that can be applied to larger families of materials, as well as combinatorial studies with complementary probes or calculations that can guide or confirm these design principles to enable rational design of complex solid-state materials.

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