As a materials science expert, I've spent considerable time studying the properties of metals and their behavior under various conditions. One of the fundamental characteristics of metals is their electrical conductivity, which is a result of the movement of free electrons within the metal lattice. Now, let's delve into the question at hand: Why does the conductivity of metals decrease with increasing temperature?

The electrical conductivity of a metal is primarily determined by the number of free electrons available for conduction and the ease with which these electrons can move through the material. This movement is influenced by the lattice structure of the metal and the presence of impurities or defects that can scatter the electrons.

When we consider the effect of temperature on conductivity, we must understand the dual role that temperature plays. On one hand, increasing temperature can increase the kinetic energy of the free electrons, which might seem to suggest that conductivity would increase as well. However, this is not the whole story.

The key to understanding the decrease in conductivity with temperature lies in the concept of lattice vibrations, or phonons. As the temperature of a metal increases, the atoms in the metal lattice begin to vibrate more vigorously. These vibrations are a form of thermal energy that can interact with the free electrons. The increased vibrations lead to more frequent collisions between the electrons and the lattice atoms. This scattering of electrons by the vibrating lattice atoms disrupts the flow of electrons, which in turn reduces the overall conductivity of the metal.

Moreover, the mean free path—the average distance an electron can travel before colliding with another particle—is reduced at higher temperatures due to the increased frequency of these collisions. The reduction in the mean free path is a critical factor in the decrease of conductivity.

It's also important to note that the presence of impurities or defects in the metal can further reduce conductivity. These imperfections in the lattice can act as additional scattering centers for the electrons, exacerbating the decrease in conductivity with increasing temperature.

In summary, while the initial increase in electron kinetic energy with temperature might suggest an increase in conductivity, the dominant effect is the increased scattering of electrons due to lattice vibrations and impurities, which leads to a decrease in conductivity as temperature rises.

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For metals, the thermal conductivity is mainly a function of the motion of free electrons. As the temperature increases, the molecular vibrations increase (in turn decreasing the mean free path of molecules). So, they obstruct the flow of free electrons, thus reducing the conductivity.read more >>