Graduate Thesis Or Dissertation
 

Single crystal growth, powder synthesis and characterization of layered chalcogenide semiconductors

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/th83m144g

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  • This thesis presents basic studies, including structural, optical and transport measurements, on novel chalcogenide powders and single crystals. BiCuOSe crystals have been synthesized for the first time. The crystal structure of BiCuOSe has been refined and the optical band gap has been measured to be 0.83eV. Crystal structure refinements of new crystals Sn₁.₇₈Zr₀.₂₂S₃ and SnZrSe₃ are also reported. BiCuOTe powder has been synthesized by a novel precursor method. Using this synthesis route, the solid solutions BiCuOS₀.₅Se₀.₅ and BiCuOSe₀.₅Te₀.₅ were made. Lattice parameters were measured for the BiCuO(S,Se) and BiCuO(Se,Te) solid solution range; Vegard's law is obeyed. Optical gap measurements were possible for BiCuO(S,Se) which showed a near linear relationship. Studies of SnMCh₃ (M = Zr and Hf; Ch = S and Se) show the incorporation of many dopants on the M site including In, Sb, Bi, Y and Nb. Seebeck measurements of the powders show that SnZrS₃ and SnZrSe₃ are intrinsically p-type materials. These materials become n-type semiconductors with the addition of Sb and Bi. A solid solution forms between SnZrS₃ and SnZrSe₃. Both lattice parameters and optical band gaps vary smoothly between the end members. Density functional theory was used to determine that these materials are indirect semiconductors and to predict the optical band gaps. The calculated band gaps vary from 0.5eV for Sn₂S₃ and SnZrSe₃ to 1eV for SnHfS₃. Measured optical band gaps range from 0.83eV for SnZrSe₃ to 1.4eV for SnHfS₃. The material Cu₃TaSe₄ will accept Zr and P into its structure without deformation at 5 at. %, but not W.
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