Temperature Dependence of Resistance for Alloys

Temperature Dependence of Resistance for Alloys

The resistance of most conductive materials changes with temperature.temperature coefficient of resistance for alloys The rate of this change is known as the temperature coefficient of resistance and can be expressed as: a (Rref - T)/(Tref) where Rref is the resistance of the material at its reference temperature and T is the temperature change. For pure metals and alloys, this is a constant value that does not vary much with temperature, but for semiconductors and other insulating materials, it can be quite different.

There are several reasons why the temperature dependence of resistance can vary so much.temperature coefficient of resistance for alloys The most basic reason is that the number of charge carrier collisions with atoms in a material increases as temperature rises, as the electrons acquire greater kinetic energy and are more frequently scattered from their regular lattice structure. This increases the time it takes for an electron to reach its destination in a metal and therefore results in an increase in the resistance.

A second reason is that atomic vibrations can impede the flow of electrons, even at very low temperatures.temperature coefficient of resistance for alloys This is not as pronounced for metals and other materials at room temperature, but it can still be significant at very low temperatures.

These two factors result in a characteristic curve of resistance versus temperature for most materials, with the slope of the curve changing as the material is heated or cooled. The temperature coefficient of resistance is the difference in this curve, and it can be calculated from the equation:

In pure metals, the temperature coefficient of resistance is positive, meaning that the resistance of a metal increases with increasing temperature. For alloys, the temperature coefficient of resistance is a little lower, since different metals have slightly different properties compared to each other. The alloy of manganin (which consists of copper, manganese and nickel), for example, has close to zero temperature dependence, so it is useful for making temperature-independent resistance standards.

In semiconductors and insulators, the temperature coefficient of resistance is negative. This is because when electrons move from their valence bands into the conduction bands, they must pass through a forbidden energy gap that has a small barrier potential. This is why the resistance of a semiconductor or an insulator decreases with temperature, as more electrons are free to move through the gap. A graph of resistance versus temperature for various DNI alloys and pure elements is shown in Figure 1, with the line for each material proportional to its TCR.