Synthesis and Crystal Growth of Layered Chalcophosphate and Framework Chalcoborate Compounds Using Reactive Flux and Chemical Vapor Transport Methods

Chica, Daniel George

doi:https://doi.org/10.21985/n2-jtek-xh13

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Synthesis and Crystal Growth of Layered Chalcophosphate and Framework Chalcoborate Compounds Using Reactive Flux and Chemical Vapor Transport Methods

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The crystal structure of chalcogenides can vary from simple, ubiquitous structures of rock salt and zinc blende to unique structure types from the intricate packing of complex anionic building blocks. Exploratory synthesis and structural studies of novel chalcogenides containing these complex anions will augment the understanding of bonding in chalcogenides. Herein this thesis, the synthesis, crystal growth, structure, and physical properties of several novel chalcogenides containing chalcophosphate and chalcoborate polyanions, are described. For the chalcophosphate class these compounds include LiInP2Se6, SnP2Se6, MnCoP2S6, and FeCoP2S6, and for the chalcoborates class they include Sn4B12Se12[Se3.80], Sn3.92B12Se12[Se0.61], and Sn3.88B12Se12[Te3.53]. The individual layers of these chalcophosphates compounds have the same [P2Q6]4- , Q = S, Se sublattice. However, because the valence of the cations differs between these compounds, the cation ordering in the individual layers differs as well. The stacking sequence for the thiophosphates, LiInP2Se6, and SnP2Se6 are AA, ABAB, and ABCABC, respectively. LiInP2Se6 shows promise as a neutron semiconductor detector material which was demonstrated by the energy resolution of 13.9% and 69.7% for the peak of the pulse height spectra of alpha particles (241Am source) and thermalized neutrons (Pu/Be source), respectively. The tin boron chalcogenides described are tunnel framework compounds containing the rare polyanion, [B12Se12]14- that have varying amounts of selenium or tellurium in the tunnels of the structure depending on the preparation. This series of framework compounds have bandgaps between 1.32 – 1.69 eV and remarkable thermal stability and chemical stability towards strong acids and bases. Chemical vapor transport was crucial in the preparation of detector grade LiInP2Se6 while for SnP2Se6 this method was the only way to grow large single crystals. Reactive fluxes of Sn/Se were necessary for the synthesis of the Sn4B12Se12[Se3.80] as this material cannot be made from the direct combination of the elements. The reaction times for the synthesis of layered thiophosphates have been shorted to on the order of hours and days rather than weeks and months using the newly developed P2S5 reactive flux method. The synthetic methods described in this thesis have great potential for the discovery of novel chalcophosphate and chalcoborate materials.

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