Examining the electronic structure of metal pnictides via X-ray spectroscopy

  • Author / Creator
    Blanchard, Peter Ellis Raymond
  • Given the wide range of properties and applications of intermetallic compounds, it is important to achieve a detailed understanding of their structure and bonding. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) were used to study the electronic structure of several types of pnictides (compounds containing Pn = P, As). ZrAs2, forming a PbCl2-type structure, has been established to be a genuine binary phase that is strictly stoichiometric. At 900 °C, it supports extensive solubility of Ge to form the ternary extension Zr(GexAs1−x)As (0 ≤ x ≤ 0.4). XPS analysis and band structure calculations confirmed that the Ge and As atoms are anionic in character and that the substitution of Ge for As is driven by a depopulation of anion–anion antibonding states. ZrCuSiPn and REMAsO are important representatives of ZrCuSiAs-type materials. The small magnitudes of the binding energy shifts in the XPS spectra of ZrCuSiPn suggest significant covalent character in the Zr–Si, Zr–Pn, and Cu–Pn bonds, consistent with a three-dimensional structure. On progressing from ZrCuSiP to ZrCuSiAs, the charge transfer from metal to Pn atoms becomes less pronounced, as indicated by changes in the intensity of the Cu K-edge and Zr K, L-edge XANES spectra. Binding energy shifts and satellite features of the XPS spectra of REMAsO indicated that bonding in the [REO] layer is ionic, whereas bonding in the [MAs] layer is strongly covalent. Altering the electronic structure of one layer (by M or RE substitution) does not affect the electronic structure of the other layer, consistent with a two-dimensional structure in REMAsO. Metal-rich phosphides M2P (forming Cr2P-, Fe2P-, and Co2P-type structures) and M3P (forming Ni3P-type structures) were examined by XPS and XANES. The P 2p3/2 binding and P K-edge absorption energies decrease with greater ionic character of the M−P bonding and indicate the presence of anionic phosphorus. Interatomic effects play a more important role in affecting the energy shifts in these metal-rich phosphides than in the monophosphides, becoming more pronounced with higher metal concentration. Surprisingly, intraatomic effects dominate in mixed-metal phosphides (Ni1-xMx)2P despite evidence of metal-to-metal charge transfer from the Ni XANES spectra and Ni 2p XPS satellite features.

  • Subjects / Keywords
  • Graduation date
    Fall 2011
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
  • Supervisor / co-supervisor and their department(s)
  • Examining committee members and their departments
    • Prof. Michael J. Serpe, Chemistry
    • Prof. Zhenghe Xu, Chemical and Materials Engineering
    • Prof. Jonathan G.C. Veinot, Chemistry
    • Prof. Stephanie L. Brock, Chemistry, Wayne State University
    • Prof. Alexander Brown, Chemistry