Structure determination by X-ray diffraction methods and physicochemical characterization of quaternary diamond-like semiconductors.

摘要

Diamond-like semiconductors (DLSs) are a class of semiconductor materials having structures similar to that of either cubic or hexagonal diamond. These normal valence compounds are of interest for their wide variety of technologically useful properties that can be tuned for specific applications. Until recently, DLS research has been focused on binary and ternary compositions due to their relative ease of synthesis. However, quaternary DLSs have gained considerable popularity due to their increased compositional flexibility and their potential as multifunctional materials. Despite their growing reputation, the vast number of possible combinations and conceivable solid solutions, DLSs remain fairly unexplored.;This work focuses on quaternary DLSs of the formula Ag2-II-IV-S4 in order to advance the knowledge of structure-property relationships for this entire class of materials. Toward this goal, a more complete understanding of the crystal structures of these materials is necessary. This task is often problematic due to the presence of isoelectronic, or nearly isoelectonic elements, that can complicate X-ray structure refinements. In this work, Ag2CdGeS 4 is used as a case study to demonstrate that this problem can be resolved with careful consideration of bonding environments as well as the use of high-resolution X-ray sources. For the novel DLS Ag2ZnSiS4, the relationship between the structure and optical properties is probed with the combination of single crystal X-ray diffraction, optical diffuse reflectance spectroscopy and electronic structure calculations using the software package Wien2k. Finally, the current set of predictive tools employed to forcast diamond-like structures are reviewed, including the adherence of these guidelines to the novel compound Ag2FeSiS4 as well all over 60 ternary and quaternary diamond-like materials currently reported in the literature. Furthermore, the most common radii sets used for the prediction of bond distance and cell parameters in these materials are compared to the observed bond distances in quaternary diamond-like nonoxide materials.