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Uncrossing of Fermi level by d-electrons of Cu, Ag, Au

  1. Aug 3, 2015 #1
    I encounter contradictive informations about this issue which is supposed to define "real noble metals"
    is this statement correct at absolute zero or at any temperature?
    Does it include ds hybridizations?
     
  2. jcsd
  3. Aug 3, 2015 #2

    ZapperZ

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    It would be nice if you actually provide citations and references to show these apparent contradictions. This should be a common practice here in this forum.

    Zz.
     
  4. Aug 4, 2015 #3
    Here are some refs, to name few, discussing density of states at the Fermi level
    S.K.Bose in J.Phys.Condens. matter 21 (2009) p. 1- "Electron-phonon coupling... in 3d and 4d transition metals... etc"
    gives Nd 1.99 for Cu, 1.03 for Ag
    I.I.Mazin et al J.Phys.F: Met. Phys. 14 (1984) p 167-174 "Electron-phonon effects in 4d metals.. etc" gives N(0) 3.56 for Ag (although small is not 0)
     
  5. Aug 5, 2015 #4

    DrDu

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    What exactly do you mean with "uncrossing"?
     
  6. Aug 5, 2015 #5
    Here is a quotation from Wikipedia, noble metals
    Physics[edit]

    In physics, the definition of a noble metal is most strict. It requires that the d-bands of the electronic structure are filled. From this perspective, only copper, silver and gold are noble metals, as all d-like bands are filled and do not cross theFermi level.[9]
     
  7. Aug 5, 2015 #6

    ZapperZ

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    The 3d orbital for Cu is full. So it is highly localized and so, in a band structure, the 3d band will not cross the Fermi level. It is the 4s band that crosses the Fermi level.

    Zz.
     
  8. Aug 5, 2015 #7
    Thanks Zz. In this case how you explain Nd for copper =1.99?
     
  9. Aug 6, 2015 #8
    May I repeat, Nd for copper and silver, 1.99 and 1.03 resp. are low vs. other metals, e.g. Pd = 30.6
    and comparable with Pb(0.99), Al(1.62), Cd(0.35) but not 0
     
  10. Aug 7, 2015 #9

    DrDu

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    You are right that this probably is a question of hybridization. The bands arising from the overlap of the atomic d-orbitals will admix contributions from other orbitals and vice versa also the orbitals in other bands will get some admixture of d-orbitals which are probably responsible for the non-vanishing d-orbtial density at the Fermi energy.
    So you have to consider the following hypothetical process, which can be done very well with quantum solid state packages: If you increase the spacing of the atoms in the metal continuously, will there be a band which is completely filled at the start and goes over into the d-orbitals at large separation of the atoms?
     
  11. Aug 8, 2015 #10
    Or vice versa. In Al the population of d increases with pressure. "calculated pressure induced fcc-hcp phase transition
    in aluminum" by H.Dagistanli, Bitlis Eren Univ J Sci & Technol, ISSN 2146-7706, 3 (2013), 6-8
     
  12. Aug 11, 2015 #11
    According with this discussion parts of my booklet "Gold electronic enigma, 1, 2 or 3" have been updated.
    1st part to be updated:
    2.Why they are noble?

    Noble metals are a particular case of transition metals. Those with relativistic contraction (i.e. full 5d-band), comprising the heavy group, are even more unique.
    Gold is found in nature as pure material. Pure silver and mercury result from their compounds by the action of light, heat...When the nuclei of metals become larger, the attraction between the nuclei and the electrons becomes stronger. Proceeding higher in the periodic table d-shells begin to be filled, s is already occupied or half of it. The electrons occupying the d-shells have higher energy than s-shell. They join in part s-electrons, forming the sea of electrons. Gold, silver and copper are different, having minimal hybridization amount, what results in 1) Lower melting points (softer metals). 2) Highest conductivities. This sea of electrons is the glue causing most transition metals to be so dense, hard and of high MP's. In contrast – metals without partly empty d-shell are softer, of lower MP's and higher atomic diameters. In case of reaction or conduction, most transition metals, d-electrons hybridized with s-electrons, make them sluggish, or directional rather than free, resulting in less conductivity and delayed reaction rates (passivation, kinetical delay). At one point, where the list of noble metals light group begins (Ru, Rh, Pd, Ag), said attraction and enveloping glue are combined in raising the oxidation potential thus protecting any particular electron from reacting. In the heavier group (Re, Os, Ir, Pt, Au, Hg), the relativistic contraction (p. 16) makes it still harder, stabilizes further the contracted atoms.
     
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