Synthesis and characterization of novel group VI metal (Mo, W) nitride and oxide compounds

Thesis/Dissertation · Mon Feb 23 00:00:00 EST 1998

DOI:https://doi.org/10.2172/587893· OSTI ID:587893

Zhang, Zhihong ^[1]

---

1. Iowa State Univ., Ames, IA (United States)

Investigations into the preparation of tungsten nitrides have involved the synthesis of molecular precursors, and their conversion to tungsten nitrides at relatively low temperatures. Two interesting molecular precursors, [WNCl₃∙NCCH₃]₄ and WN(N₃)₃∙xNCCH₃, have been prepared and characterized. The molecular structure of the first consists of a W₄N₄ tetrameric core with multiple and single W-N bonds arranged in an alternating fashion. Three new solid state phases, amorphous W₃N₅, cubic WN, and W₂N₂(C₂N₂), have been discovered by solid state and chemical vapor transport reactions. The structures have been investigated. A systematic study in the Ln₂O₃-MoO₃-Mo (Ln = La, Ce, Pr, Nd, Sm) system has been explored to better understand LnMo₈O₁₄. The study has shown that the sizes of the rare-earth cations affect the formation of these phases. Larger cations (La, Ce, and Pr) aid in the formation of trans-Mo₈ bicapped octahedra, and the smaller cations (Nd, Sm) only stabilize the cis-Mo₈ bicapped octahedra. Magnetic susceptibility measurements have indicated that no effective moment contribution arises from the Mo₈ metal clusters, even though the cis-Mo₈ cluster in LnMo₈O₁₄, containing all cis-Mo₈ octahedra, apparently contains an odd number of electrons (23). Electrical resistivity measurements and electronic structure calculations have shown that the LnMo₈O₁₄ compounds containing cis-Mo₈ clusters are metallic, and the LnMo₈O₁₄ compounds containing a 1:1 ratio of cis- to trans-Mo₈ clusters are semiconducting.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 587893
• Report Number(s): IS-T-1829; ON: DE98004649; TRN: 98:009463
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: 23 Feb 1998
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
TUNGSTEN NITRIDES
LANTHANUM OXIDES
MOLYBDENUM OXIDES
CERIUM OXIDES
NEODYMIUM OXIDES
SAMARIUM OXIDES
PRASEODYMIUM OXIDES
PRECURSOR
MOLECULAR STRUCTURE
FABRICATION
MAGNETIC SUSCEPTIBILITY
ELECTRIC CONDUCTIVITY
PHASE STUDIES