2.1.4 Summary to: Conductors - Definitions and General Properties
- Page ID
- 2757
What counts are the specific quantities:
- Conductivity σ (or the specific resistivity ρ = 1/ σ.
- current density j.
- (Electrical) field strength · E.
\[\sigma=|q|\cdot n\cdot \mu\\\underline{j}=\sigma\cdot\color{purple}{\underline{E}}\]
σ (of conductors / metals) obeys (more or less) several rules; all understandable by looking at n and particularly µ.
Matthiesen rule: |
\[\rho=\rho_\text{Lattice}(T)+\rho_\text{defect}(N)\] |
"ρ(T) rule": |
\[\Delta\rho=\alpha_\rho\cdot\rho\cdot\Delta T\approx\frac{0.4\%}{^\text{o}C}\] |
Nordheim's rule: |
\[\rho \approx \rho_\text{A}+\text{const.}\cdot [B]\] |
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) | ρ(decent metals) about 2 μΩcm. ρ(technical semiconductors) around 1 Ω cm. ρ(insulators) > 1 GΩcm. |