Electrical resistivity variation with temperature, metals

FIGURE 8 Sketch to indicate the variation of electrical resistivity p with temperature 7 in a metal. In the limit of very low temperatures, p usually approaches a constant value, po, known as the residual resistivity. 

The thermisters (TMs) are semiconductor device with a high resistance dependence on temperature. They may be calibrated as a thermometer. The semiconductor sensor exhibits a large change in resistance that is proportional to a small change in temperature. Normally TMs have negative thermal coefficients. Like RTDs, they operate on the principle that the electrical resistance of a conductive metal is driven by changes in temperatures. Variations in the conductor s electrical resistance are thus interpreted and quantified, as changes in temperature occur. 

Metal Oxide-Polymer Thermistors. The variation of electrical properties with temperature heretofore described can be used to tremendous advantage. These so-called thermoelectric effects are commonly used in the operation of electronic temperature measuring devices such as thermocouples, thermistors, and resistance-temperature detectors (RTDs). A thermocouple consists of two dissimilar metals joined at one end. As one end of the thermocouple is heated or cooled, electrons diffuse toward... 

In 1908, Kamerlingh Onnes succeeded in liquefying helium, and this paved the way for many new experiments to be performed on the behaviour of materials at low temperatures. For a long time, it had been known from conductivity experiments that the electrical resistance of a metal decreased with temperature. In 1911, Onnes was measuring the variation of the electrical resistance of mercury with temperature when he was amazed to find that at 4.2 K, the resistance suddenly dropped to zero. He called this effect superconductivity and the temperature at which it occurs is known as the (superconducting) critical temperature, Tc. This effect is illustrated for tin in Figure 10.1. One effect of the zero resistance is that no power loss occurs in an electrical circuit made from a superconductor. Once an electrical current is established, it demonstrates no discernible decay for as long as experimenters have been able to watch ... 

Another well proved pressure gauge is equipped with a metallic membrane cell [54], The principle of this cell is the inclination of the membrane which causes the pressure-proportional variation of the electrical resistance of the system. The pressure range of those systems reaches up to 400 bar. The allowable temperatures of the metering system are near... 

Figure 5.9 shows the variation in resistivity of three metals with temperature. In each case, p increases with temperature, and the electrical conductivity (which is the inverse of the resistance) decreases as the temperature is raised. This property distinguishes a metal from a semiconductor, which is a material in which the electrical conductivity increases as the temperature increases (Figure 5.10). 

The interaction between impurity ions with partially filled d or f electron shells and the conduction electrons of a metallic host can lead to variations in certain physical properties with temperature and magnetic field which have come to be associated with the Kondo effect . In zero magnetic field, these temperature-dependent anomalies in the physical properties scale with a characteristic temperature Tk, the so-called Kondo temperature, above which the matrix-impurity system behaves magnetically and below which the matrix-impurity system behaves nonmagnetically. The physical properties which exhibit anomalies attributable to the Kondo effect include the electrical resistivity, magnetic susceptibility, thermoelectric power, specific heat and, in systems where appropriate, superconducting properties such as the critical temperature and the jump in specific heat which occurs at T. ... 

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