Principle of diamond thermal conductivity

Diamond is a cubic crystal structure, each carbon atom is a SP3 hybrid orbital with the other 4 carbon atoms to form a covalent bond, forming a regular tetrahedron, because all the valence electrons are limited to the covalent bond region, there are no free electrons, so the diamond is not conductive. High thermal conductivity is associated with high electrical conductivity, and unlike metals that rely on peripheral electrons for heat transfer, diamond's thermal conductivity basically comes from the propagation of carbon atom vibrations (i.e., phonons).

The mean free path of phonons is determined by the collisions between phonons and the scattering of phonons by defects in solids. Impurity elements, dislocation, cracks and other crystal defects in diamond, residual metal catalysts and lattice orientation will collide with phonons and scatter them, thus limiting the mean free path of phonons and reducing thermal conductivity.

When the composition of the substance is simpler, the structure is simpler, and the impurities are less, the phonon movement is faster, and the heat transfer rate is faster. This is because the introduction of the second component and impurities can cause lattice distortion, distortion and dislocation, destroy the integrity of the crystal, and increase the scattering probability of phonons or electrons. Diamond is composed of only a single element carbon, the structure is also very simple, Ia, Ib, IIa and IIb four kinds of diamonds, IIa pure, less impurities, so it has a high heat transfer rate.

In the past, when buying diamonds, someone will lick the tip of the tongue, if the tip of the tongue feels cool, it is true diamond; If it's warm, it's just glass. This process is actually using the tip of the tongue as a probe to do a comparative thermal conductivity experiment on the gem. Because the thermal conductivity of glass is very small, and the heat transfer rate of real drill is more than a thousand times that of glass, so it is really easy to tell the difference between the two.

In addition, diamond also has the characteristics of high resistivity and high breakdown field strength, low dielectric constant, low thermal expansion, etc., which has obvious advantages in the heat dissipation problem of high-power optoelectronic devices, which also shows that diamond has great application potential in the field of heat dissipation.