Resistivity of Various Materials
- A conductor such as a metal has high conductivity and a low resistivity.
- An insulator like glass has low conductivity and a high resistivity.
- The conductivity of a semiconductor is generally intermediate, but varies widely under different conditions, such as exposure of the material to electric fields or specific frequencies of light, and, most important, with temperature and composition of the semiconductor material.
The degree of doping in semiconductors makes a large difference in conductivity. To a point, more doping leads to higher conductivity. The conductivity of a solution of water is highly dependent on its concentration of dissolved salts, and other chemical species that ionize in the solution. Electrical conductivity of water samples is used as an indicator of how salt-free, ion-free, or impurity-free the sample is; the purer the water, the lower the conductivity (the higher the resistivity). Conductivity measurements in water are often reported as specific conductance, relative to the conductivity of pure water at 25 °C. An EC meter is normally used to measure conductivity in a solution. A rough summary is as follows:
| Material | Resistivity ρ (Ω•m) |
| Superconductors | 0 |
| Metals | 10−8 |
| Semiconductors | variable |
| Electrolytes | variable |
| Insulators | 1016 |
This table shows the resistivity, conductivity and temperature coefficient of various materials at 20 °C (68 °F)
| Material | ρ (Ω•m) at 20 °C | σ (S/m) at 20 °C | Temperature coefficient (K−1) |
Reference |
|---|---|---|---|---|
| Silver | 1.59×10−8 | 6.30×107 | 0.0038 | |
| Copper | 1.68×10−8 | 5.96×107 | 0.0039 | |
| Annealed copper | 1.72×10−8 | 5.80×107 | ||
| Gold | 2.44×10−8 | 4.10×107 | 0.0034 | |
| Aluminium | 2.82×10−8 | 3.5×107 | 0.0039 | |
| Calcium | 3.36×10−8 | 2.98×107 | 0.0041 | |
| Tungsten | 5.60×10−8 | 1.79×107 | 0.0045 | |
| Zinc | 5.90×10−8 | 1.69×107 | 0.0037 | |
| Nickel | 6.99×10−8 | 1.43×107 | 0.006 | |
| Lithium | 9.28×10−8 | 1.08×107 | 0.006 | |
| Iron | 1.0×10−7 | 1.00×107 | 0.005 | |
| Platinum | 1.06×10−7 | 9.43×106 | 0.00392 | |
| Tin | 1.09×10−7 | 9.17×106 | 0.0045 | |
| Carbon steel (1010) | 1.43×10−7 | 6.99×106 | ||
| Lead | 2.2×10−7 | 4.55×106 | 0.0039 | |
| Titanium | 4.20×10−7 | 2.38×106 | X | |
| Grain oriented electrical steel | 4.60×10−7 | 2.17×106 | ||
| Manganin | 4.82×10−7 | 2.07×106 | 0.000002 | |
| Constantan | 4.9×10−7 | 2.04×106 | 0.000008 | |
| Stainless steel | 6.9×10−7 | 1.45×106 | ||
| Mercury | 9.8×10−7 | 1.02×106 | 0.0009 | |
| Nichrome | 1.10×10−6 | 9.09×105 | 0.0004 | |
| GaAs | 5×10−7 to 10×10−3 | 5×10−8 to 103 | ||
| Carbon (amorphous) | 5×10−4 to 8×10−4 | 1.25 to 2×103 | −0.0005 | |
| Carbon (graphite) | 2.5e×10−6 to 5.0×10−6 //basal plane 3.0×10−3 ⊥basal plane |
2 to 3×105 //basal plane 3.3×102 ⊥basal plane |
||
| Carbon (diamond) | 1×1012 | ~10−13 | ||
| Germanium | 4.6×10−1 | 2.17 | −0.048 | |
| Sea water | 2×10−1 | 4.8 | ||
| Drinking water | 2×101 to 2×103 | 5×10−4 to 5×10−2 | ||
| Silicon | 6.40×102 | 1.56×10−3 | −0.075 | |
| Deionized water | 1.8×105 | 5.5×10−6 | ||
| Glass | 10×1010 to 10×1014 | 10−11 to 10−15 | ? | |
| Hard rubber | 1×1013 | 10−14 | ? | |
| Sulfur | 1×1015 | 10−16 | ? | |
| Air | 1.3×1016 to 3.3×1016 | 3×10−15 to 8×10−15 | ||
| Paraffin | 1×1017 | 10−18 | ? | |
| Fused quartz | 7.5×1017 | 1.3×10−18 | ? | |
| PET | 10×1020 | 10−21 | ? | |
| Teflon | 10×1022 to 10×1024 | 10−25 to 10−23 | ? |
The effective temperature coefficient varies with temperature and purity level of the material. The 20 °C value is only an approximation when used at other temperatures. For example, the coefficient becomes lower at higher temperatures for copper, and the value 0.00427 is commonly specified at 0 °C.
The extremely low resistivity (high conductivity) of silver is characteristic of metals. George Gamow tidily summed up the nature of the metals' dealings with electrons in his science-popularizing book, One, Two, Three...Infinity (1947): "The metallic substances differ from all other materials by the fact that the outer shells of their atoms are bound rather loosely, and often let one of their electrons go free. Thus the interior of a metal is filled up with a large number of unattached electrons that travel aimlessly around like a crowd of displaced persons. When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming what we call an electric current." More technically, the free electron model gives a basic description of electron flow in metals.
Read more about this topic: Electrical Resistivity And Conductivity
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