The synthesis and characterization of compounds with framework elements of contrasting reactivities {B, Si}-{P, As}

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Woo, Katherine
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Kirill Kovnir
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The Department of Chemistry seeks to provide students with a foundation in the fundamentals and application of chemical theories and processes of the lab. Thus prepared they me pursue careers as teachers, industry supervisors, or research chemists in a variety of domains (governmental, academic, etc).

The Department of Chemistry was founded in 1880.

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The reactivity difference between boron or silicon with phosphorus or arsenic creates challenges in synthesis. Synthesizing ternary compounds increases the level of complexity. The syntheses of new multinary compounds consisting of covalent bonds between these elements of drastically different reactivities have been investigated, and the resulting products were characterized.

Between silicon and arsenic, a completely new set of compounds in the Mg-Si-As system were discovered, as well as a highly versatile family of Cs0.16MxSi1-xAs2 (M = Cu, Zn, Ga). Compounds in the Mg-Si-As system seem to show a preference with crystalizing in non-centrosymmetric space groups, which is uncommon through solid state synthesis methods. MgSiAs2 has been studied theoretically for years, but had never been realized experimentally. With its now successful synthesis, MgSiAs2 displays a good balance of second harmonic generation response and laser damage threshold. Mg3Si6As8 has a space group of P4332 (No. 212), which is in the one Laue class, 432, that does not allow second harmonic generation, but electronic structure calculations suggest the compound may be used as a thermoelectric material upon doping. Layered Cs0.16MxSi1-xAs2 (M = Cu, Zn, Ga) compounds show potential as a thermoelectric material due to the anisotropic 2D crystal structure. Their ability to substitute various metals into the layered framework without altering the crystal structure introduces the option of tuning the material.

Using BI3 as a boron source was investigated for the reaction with phosphorus and various metals. This method allowed BP to be synthesized very quickly at moderate temperatures and with low contamination compared to flux reactions or the direct reaction of boron and phosphorus. These advantages transferred to the synthesis of metal borides, and Ni2CoB was produced when starting with a NiCo alloy. To explore the formation of metal boron phosphide compounds containing covalent B-P bonds, solid state metathesis between Na3BP2 and metal halides, mainly CuCl, was performed. In situ powder X-ray diffraction experiments were utilized in conjunction with lab experiments to gain insight on a new “Na-Cu-B-P” compound. Surprisingly, a new non-centrosymmetric Na2BP2 compound with the space group of Pna21 (No. 33) was discovered in a reaction of leaching Na from Na3BP2 using CuI and a CsI/NaI flux.

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