Residual-resistance ratio

The residual resistance ratio (often just RRR or RRR for Residual Resistance Ratio ) is the ratio of the resistance of a material at the absolute temperature of 293 Kelvin to the resistance of a material at very low temperatures, for example at 4 K, where no contribution of the thermal lattice vibration more expected ( residual resistivity ).

The size of the residual resistance ratio is a measure of the purity of a material. The larger the ratio, the less impurities comprises the material. At high temperatures, electron scattering in addition to the material 's solid impurities and by phonons. Since the phonons disappear in contrast to the solid impurities at low temperatures, is the ratio of the two resistors (with and without phonons) information on the proportion of solid impurities.

Superconductors usually used for the resistor is short of the transition temperature from the superconducting to the normally conducting state and the residual resistance. In the superconducting state only remains of the resistance of the leads, which can be if any, used for offset correction.

Pure aluminum has, for example, a residual resistance ratio RRR = 20,000. Typical values ​​for thin wires are on the order of about 20