Exploratory synthesis and structure/property correlation studies of novel mixed-metal sulfide and selenide compounds with quasi-low-dimensional structures and serendipitous synthesis of mixed chalcohalide compounds

[摘要] In recent years, the search for new mixed-metal chalcogenide compounds has become important for the development of new materials that can be used in advanced opto-electronic devices. The exploratory synthesis of quasi-low-dimensional chalcogenide compounds, particularly mixed-metal sulfides and selenides that contain a reduced early transition metal cation, has been investigated.Several interesting compounds with novel structures and physical properties have been isolated during the course of studies. Four mixed-metal sulfides containing reduced titanium (III) have been synthesized: (RE)$sb6$InTiS$sb{12}$ (where RE = Nd, Sm, and Gd) and Gd$sb3$TiS$sb6$. The structures of these reduced phases are characterized by pseudo-one-dimensional chains of fused TiS$sb6$ octahedra sharing opposite edges. Also, a new series of quasi-two-dimensional sulfides as well as selenides which are structurally categorized as misfit-layer compounds with the general formula ((A,M)Q) $sb6$(TQ$sb2$)$msb{5m}$ (where A = Ca, Sr; M = Bi, Pb, La, Ce, Nd, T = Ti, Nb, and Q = S, Se and m = 1, 2) has been discovered and systematically studied. In exploring mixed-metal chalcogenide systems via the molten halide flux crystal growth method, a new family of chalcohalide phases was serendipitously synthesized. These newly discovered chalcohalide compounds, CdBiQ$sb2$X (Q = S, X = Cl, Br; Q = Se, X = Br, I), possess an interesting layered-like structure in which the anion ordering is governed by the size difference between the chalcogen (S$sp{2-}$ and Se$sp{2-}$) and halogen (Cl$sp-$, Br$sp-$, and I$sp-$) anions. The detailed discussion is in results part I, II, and III, respectively.Synthetically, a conventional high-temperature solid-state ceramic method has been employed for the bulk synthesis. Vapor transport and/or molten salt flux methods have been used to grow sizable single crystals for structure characterization and physical property measurements. Several analytical techniques have been utilized to characterize these new materials, such as single crystal and powder X-ray diffraction, Weissenberg X-ray photography, thermal analysis (DTA), and four-probe conductivity measurements. Other relevant techniques for characterization of inorganic solids were also used, e.g., electron microscopy, infrared (reflectance) spectroscopy. This study provides necessary understanding of phase compatibility in mixed-cation and mixed-anion systems and in turn for the future design synthesis of advanced chalcogenide materials.

[发布机构] Rice University

[效力级别] chemistry