Synthesis and Characterization of Rotationally Disordered Intergrowths Containing PbX and TiX2 (X = Se and Te)
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The method of modulated elemental reactants (MER) is used to prepare the layered compound Ti1+xSe2. Using a thin-film precursor prepared by sequentially depositing elemental titanium and selenium by physical vapor deposition, the binary compound is readily formed by short-duration annealing at 350°C. The structural and electrical properties of this compound are investigated and suggest that the film is markedly different from the bulk crystalline material. The synthesis is then expanded to produce the first TiSe2 turbostratically disordered misfit layer compound, (PbSe)1.16TiSe2. With the synthesis technique established, the second compound in this family, (PbSe)1.18(TiSe2)2, was synthesized and compared to the misfit layer compound synthesized by bulk methods. The rotationally disordered compound demonstrated an increased Seebeck coefficient and reduced resistivity at room temperature, sparking interest in this family of compounds as potential thermoelectric materials. Designed synthesis of several targeted compounds is reported with interest in evaluating thermoelectric potential of these rotationally disordered compounds. The first nine members of this family were synthesized with m and n values 1 - 3 and evaluated for their thermoelectric properties. Results from this study indicated compounds with larger n values could be of further interest and many more of these compounds are synthesized and reported. Designed synthesis using the MER synthesis method is then pushed further to synthesize the first telluride misfit layer compounds. Four new compounds of the [(PbTe)1.17]m(TiTe2)n family are reported, and their structures were examined by a variety of X-ray diffraction techniques. The robustness of the MER method is revealed by the synthesis of these layered intergrowths which would not be possible using other synthesis methods available. This work consists, in part, of previously published and coauthored material.