2.2.4 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%
oC
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! Batteries, fuel cells, sensors, ... Example: MoSi2 for heating elements in corrosive environments (dishwasher!). The future High-Tech key materials?
Ionic conductors (liquid and solid).
Conductors for high temperature applications; corrosive environments, ..
(Graphite, Silicides, Nitrides, ...).

Organic conductors (and semiconductors).

Numbers to know (order of magnitude accuracy sufficient)
 r(decent metals) about 2 mWcm. r(technical semiconductors) around 1 Wcm. r(insulators) > 1 GWcm.

 Questionaire All Multiple Choice questions to 2.1