DEFECT AND ORDERED TUNGSTEN OXIDES ENCAPSULATED INSIDE 2H-WX2 (X=S AND Se) FULLERENE-RELATED STRUCTURES

摘要

Complex tungsten oxides, consisting of nonstoichiometric oxides of the form WO3-x and stoichiometric lamellar oxides of the form {001}R WnO3n-1 (n=3 to 6) have been observed incorporated within 2H-WX2 (X=S or Se) inorganic fullerene-like (IF) structures by HRTEM. These encapsulates were formed from a gas-solid reaction between H2X and disordered WO3-x precursors exhibiting a range of particle sizes and morphologies. The microstructures of most of the encapsulated oxides could be described in terms of {hkl}R crystallographic shear (CS) structures formed relative to an ReO3-type (R) substructure. Smaller spheroidal WO3-x encapsulates were frequently found to exhibit random {103}R CS defects of the Wadsley type, while larger, needle encapsulates were found to form exclusively {001}R WnO3n-1 type lamellar structures that were predominantely ordered. Spheriodal encapsulates with randomly spaced {001}R CS planes were also observed encapsulated inside 2H-WSe2 IF structures. The growth and morphologies of the encapsulating 2H-WX2 shells were profoundly influenced by those of the precursor oxides used in their formation. Ordering mechanisms were proposed with respect to the formation of the ordered encapsulated oxides from the disordered precursors. 41 refs.