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Dissertation Defense: Jeremy Espano, Interdisciplinary Materials Science

Posted by on Tuesday, February 20, 2024 in News.


Jeremy Espano, Interdisciplinary Materials Science
*under the direction of Janet Macdonald

Understanding the Crystalline Landscape of Metal Chalcogenide Materials

03.01.24  |  2:30PM CST  |  214 Light Hall |

The identity and arrangement of atoms determine the properties of all crystalline solids, and when the identity of the atoms is the same, multiple arrangements and different crystalline structures can still exist. Even combinations of two atoms can be rearranged to give a wide variety of crystal structures. For example, there are eight known iron sulfides, four cobalt sulfides, and seven nickel sulfides. These crystalline solids have myriad possibilities in technological applications because of their diverse electronic, optical, magnetic, chemical, and catalytic properties. However, these applications cannot be realized without reliable synthetic routes that can target each desired crystalline phase. The synthetic routes to achieve crystalline materials are often serendipitous, mainly due to the blurred lines between precursor reactivity, decomposition mechanism, temperature, time, and concentration. While some studies have tried to understand phase control, there hasn’t been a systematic phase control study that separates mechanism that precludes phase formation from kinetics. This dissertation first examines the effect of precursor decomposition kinetics on phase determination. A library of substituted thioureas is employed with ranging reactivities, and the relationship between precursor kinetics and phase determination of multiple metal sulfide (M =Fe, Co, and Ni) crystalline systems is studied. Our results suggest that the crystalline structure of the nucleated phase is a large determinant in its overall transformation. Taking both crystal structure and precursor decomposition kinetics into consideration, we can develop rational syntheses of metal sulfides, targeting most of the known iron sulfides and synthesizing all the cobalt and six of the nickel sulfides. Our results show a control over crystalline structure not previously reported and emphasize that by considering the crystalline structures of these materials, rational phase control can be achieved. Our results show impressive advances in the field of bottom-up colloidal synthesis and material chemistry.

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