How does diamond conduct heat?

Release Time：

2024-06-27

Diamond is a cubic crystal structure, where each carbon atom is covalently bonded with four other carbon atoms in SP3 hybridized orbitals, constituting an orthotetrahedron. Because all valence electrons are confined to the covalent bond region, and there are no free electrons, diamond is not electrically conductive. High thermal conductivity is associated with high electrical conductivity. Unlike metals, which rely on peripheral electrons for heat transfer, diamond's thermal conductivity is essentially derived from the propagation of vibrations of carbon atoms (i.e., phonons).

The phonon mean free range is determined by mutual collisions of phonons and scattering of phonons by defects in the solid. Impurity elements, dislocations and cracks and other crystal defects in diamond, residual metal catalysts and lattice orientation and other factors will collide with the phonons to make them scatter, thus limiting the average free range of the phonons and reducing the thermal conductivity.

When the composition of the substance is more pure, the simpler the structure, and fewer impurities, the faster the phonon movement, the faster the rate of heat transfer. This is due to the fact that the introduction of the second component and impurities causes lattice distortions, aberrations and dislocations, destroying the integrity of the crystal and increasing the chance of scattering of phonons or electrons. Diamond is composed of only a single element, carbon, and has a very simple structure. Of the 4 types of diamonds, Ia, Ib, IIa and IIb, IIa is pure and has few impurities, and therefore possesses a high rate of heat transfer.

In the past, when buying diamonds, some people will use the tip of the tongue to lick it, if it feels cool on the tip of the tongue, it is a real diamond; if it is warm, it is just glass. This process is actually using the tip of the tongue as a probe to do a thermal conductivity comparison experiment on the gemstone. Since the thermal conductivity of glass is very small, and the heat transfer rate of a real diamond is more than a thousand times that of glass, it is indeed easy for the sensitive tongue to distinguish the difference between the two.

Besides, diamond also has high resistivity and high breakdown field strength, low dielectric constant, low thermal expansion, etc. Its obvious advantages in the heat dissipation problem of high-power optoelectronic devices also indicate that diamond has great potential for application in the field of heat dissipation.

The difference between diamond monocrystalline, polycrystalline, polycrystalline-like, polycrystalline

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