Browsing by Author "Szulczewski, Gregory J"

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    An Exploration of Bonding in V_1−x Mo_x O_2 (x ≤ 0.53) and Other Compounds
    (University of Alabama Libraries, 2022) Douglas, Tyra; Allred, Jared M.; University of Alabama Tuscaloosa
    Transition metal solid-state compounds have received much attention due to their vast array of novel functional properties. However, their use is often impeded by an insufficient understanding of the structure-property relationship. This dissertation examines bonding in two families of transition metal compounds to elucidate connections to their electronic properties, V\(_{1-x}\)Mo\(_{x}\)O\(_2\) and ZrSi. The primary focus was to understand the effects of strong metal--metal bonding on the structural disorder in V\(_{1-x}\)Mo\(_{x}\)O\(_2\), using a detailed analysis of total x-ray scattering data. This investigation established that strong metal--metal bonding enhances short-range correlations in the rutile phase while suppressing long-range correlations in the low-temperature phases, which is also accompanied by the suppression of the transition temperature and magnitude of the lattice anomaly. Together, these findings indicate that the disruption of long-range three-dimensional order can now be seen as the result of geometric frustration. This explains VO\(_2\)'s negative lattice anomaly. The total collapse of long-range three-dimensional order seems to occur around the same concentration that the lattice anomaly switches sign, identifying it as a potential order parameter. This also implies that the M1 phases of VO\(_2\) and MoO\(_2\) are distinct. The exploration of bonding in ZrSi resulted in a revised crystal structure of \(\beta\)-ZrSi (space group \(Cmcm\)) from single-crystal x-ray diffraction data, correcting the atomic position and bond distances. The revised Si--Si bond length has been modified substantially from 2.723(6) Å to 2.4411(8) Å. Additionally, a comprehensive analysis of bonding trends in early transition metal compounds closely related to FeB-type \(\alpha\)-ZrSi and CrB-type \(\beta\)-ZrSi was completed, using electronic structures calculated by the Linear Muffin-Tin Orbital (LMTO) method.
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    Surface Deposition and Characterization of Metal-Organic Frameworks As Thin Films
    (University of Alabama Libraries, 2024) Speed, Daniel; Szulczewski, Gregory J
    Metal-organic frameworks (MOFs) are a premier candidate material for next-generation functional materials in basic science and industry. These porous crystalline materials can be designed around the coordination geometry of metal ions or clusters and organic linker molecules to yield materials with controlled pore size and chemical functional groups. Surface deposited MOFs are of particular interest to applications in gas sensors. However, relatively little work has been done to understand the growth mechanism of surface deposited MOFs and how best to measure their adsorption properties relative to bulk materials. MOF thin films were deposited by a vapor-assisted conversion (VAC) technique onto a variety of substrates. Specifically, MOF thin films of UiO-67-X where X is H and NH2 and M- MOF-74 where M is Co and Ni were growth on quartz crystal microbalance (QCM) surfaces, which allowed for gravimetric measurements to determine adsorption capacity. In addition, the films were characterized by powder X-ray diffraction, vibrational spectroscopy and scanning electron microscopy (SEM). The influence of the synthesis conditions (precursor concentration, temperature, and time) on the growth mechanism of UiO-67 was studied in detail. SEM studies were able to identify a preference for solvent phase or surface growth modes by quenching the VAC process over time. The precursor concentration and modulator were found to influence the growth mode most significantly.Vapor phase adsorption experiments were conducted on compounds from the BTEX family, namely, benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p- xylene isomers. Adsorption experiments on UiO-67-H films at 30 °C yielded saturation adsorption capacities from 22.4 – 26.9 % by mass, for the BTEX compounds.Similar adsorption experiments were conducted on the BTEX compounds, except toluene, at 25 °C on M-MOF-74 films. The maximum adsorption capacity was ≈17 – 20% by mass and 36 – 42 % by mass for Ni-MOF-74 and Co-MOF-74 films, respectively. These saturation values measured in thin film materials closely match the values measured on bulk materials. The difference in adsorption capacity between Ni-MOF-74 and Co-MOF-74 has been attributed to missing linker defects caused by the decomposition of the DMF solvent.