User:Benjah-bmm27/degree/3/NLA
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Chemistry of solids, NLA
[edit]Bonding and electronic structure in solids
[edit]Metallic conductivity in transition metal oxides
[edit]- Non-stoichiometry
- The monoxides MO have the rocksalt structure
- TiOx (0.7 > x > 1.25) and VO are metallic conductors
- overlap of t2g 3d orbitals from neighbouring Ti(II) atoms results in a t2g conduction band
- MnO and NiO are insulators because their t2g 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
- TiOx (0.7 > x > 1.25) and VO are metallic conductors
- Electrical conductivity in transition metal dioxides
- Electrical conductivity in transition metal trioxides
Semiconductors
[edit]- Semiconductors
- Intrinsic semiconductors — band gap Eg is small enough that electrons from the valence band can be thermally excited to the conduction band, so T↑ leads to conduction↑
- 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)
- III-V materials e.g. GaAs (isoelectronic with Ge)
Defects and non-stoichiometry
[edit]- Crystallographic defects
- Point defects
- Vacancy defects (e.g. Schottky defects)
- Interstitial defects (e.g. Frenkel defects)
- Antisite defects
- Electronic defects
- Extended defects
- Intrinsic defects (present in pure material)
- Extrinsic defects (introduced by doping)
- Kröger–Vink Notation for heterovalent doping
- Ionic conductivity and fast ion conductors
- Point defects
- Solid oxide fuel cell