User:Benjah-bmm27/degree/3/NLA

Chemistry of solids, NLA

Bonding and electronic structure in solids

• Bonding in solids
• Band theory, Fermi level
  • Electrical insulator, semiconductor, electrical conductor
  • Photoelectron spectroscopy of solids
  • Wave vector, k
  • Band structure diagrams

Metallic conductivity in transition metal oxides

• Non-stoichiometry
• The monoxides MO have the rocksalt structure
  • TiO_x (0.7 > x > 1.25) and VO are metallic conductors
    • overlap of t_2g 3d orbitals from neighbouring Ti(II) atoms results in a t_2g conduction band
  • MnO and NiO are insulators because their t_2g 3d orbitals are too contracted to overlap due to the greater electronegativity of Mn and Ni
  • FeO and CoO are also insulators, whereas second and third row transition metal oxides are more commonly metallic conductors
• Electrical conductivity in transition metal dioxides
  • TiO₂ and VO₂
• Electrical conductivity in transition metal trioxides
  • ReO₃ — Re(VI) is d¹, lustrous red metallic conductor
    • High oxidation state Re so direct d-d orbital overlap very unlikely — partially filled π-band arises from Re(5d)-O(2p) overlap
  • WO₃ — W(VI) is d⁰, insulator
  • Na_xWO₃ — W(V) is d¹, gold-coloured metallic conductor

Semiconductors

• Semiconductors
  • Intrinsic semiconductors — band gap E_g is small enough that electrons from the valence band can be thermally excited to the conduction band, so T↑ leads to conduction↑
    • Zone refining
  • Extrinsic semiconductors — doped with As (one more e⁻ than Si or Ge, N-type) or Ga (one less e⁻ than Si or Ge, P-type)
    • N-type semiconductors
    • P-type semiconductors
  • III-V materials e.g. GaAs (isoelectronic with Ge)
    • p-n junction
      • Carrier generation and recombination
      • Photovoltaic effect
    • Transistors: npn and pnp

Defects and non-stoichiometry

• Crystallographic defects
  • Point defects
    • Vacancy defects (e.g. Schottky defects)
    • Interstitial defects (e.g. Frenkel defects)
    • Antisite defects
    • Electronic defects
  • Extended defects
    • Dislocations
  • Intrinsic defects (present in pure material)
    • Anion Frenkel defects in compounds with the fluorite structure (e.g. CaF₂, ZrO₂, UO₂)
    • Cation Frenkel defects in compounds with the antifluorite structure (e.g. Li₂O)
  • Extrinsic defects (introduced by doping)
  • Kröger–Vink Notation for heterovalent doping
  • Ionic conductivity and fast ion conductors
    • Nernst-Einstein equation
    • Silver iodide
    • Beta-alumina solid electrolytes
• Solid oxide fuel cell

Superconductors

• High-temperature superconductivity, virtual experiment
  • Cooper pairs
  • Cuprate superconductors
    • Yttrium barium copper oxide
    • Lanthanum barium copper oxide