2.1.4 Summary to: Conductors - Definitions and General Properties

What counts are the specific quantities:
  • Conductivity s (or the specific resistivity r = 1/ s.
  • current density j.
  • (Electrical) field strength · E.
[ r] = Wm
[ s] = ( Wm)–1 = S/m;
S = "Siemens"
The basic equation for s is:
n = concentration of carriers,
µ = mobility of carriers.
s  =  |q| · n · µ
Ohm's law states:
It is valid for metals, but not for all materials.
j  =   s · E
s (of conductors / metals) obeys (more or less) several rules; all understandable by looking at n and particularly µ.  
Matthiesen rule:
Reason: Scattering of electrons at defects (including phonons) decreases µ.
r =  rLattice(T) + rdefect(N)
"r(T) rule":
about 0,04 % increase in resistivity per K
Reason: Scattering of electrons at phonons decreases µ.
Dr  =   ar · r · DT  »  0,4%
Nordheim's rule:
Reason: Scattering of electrons at B atoms decreases µ.
r  »  rA + const. · [B]
Major consequence: You can't beat the conductivity of pure Ag by "tricks" like alloying or by using other materials
(Not considering superconductors).
Non-metallic conductors are extremely important.    
Transparent conductors (TCO's)
("ITO", typically oxides).
No flat panels displays = no notebooks etc. without ITO!
Ionic conductors (liquid and solid).  
Batteries, fuel cells, sensors, ...
Conductors for high temperature applications; corrosive environments, ..
(Graphite, Silicides, Nitrides, ...).
Example: MoSi2 for heating elements in corrosive environments (dishwasher!).
Organic conductors (and semiconductors).  
The future High-Tech key materials?
Numbers to know (order of magnitude accuracy sufficient)  
r(decent metals) about 2 mWcm.
r(technical semiconductors) around 1 Wcm.
r(insulators) > 1 GWcm.
All Multiple Choice questions to 2.1

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© H. Föll (Electronic Materials - Script)