Diamond has one of the most unique sets of physical properties among all of the other elements due to which sometimes one can get confused over classifying its physical properties.
So, does diamond conduct electricity? Diamond does not conduct electricity although it is a good thermal conductor. It is not possible for Pure diamond to conduct electricity as it does not have any delocalized free electrons in the outer shell of the carbon atom.
The most precious crystal used in jewelry, Diamond is one of the allotropes of carbon and it is formed deep inside the earth’s surface under high pressure and high temperature. Pure diamond is made of only carbon atoms combined in covalent bonds with other carbon atoms.
Carbon atoms constitute four electrons in its outermost shell, which is also the reason why carbon is widely essential in all the fields spanning from technology to biology.
But in the case of the diamond, each valence electron of every carbon atom composes a covalent bond with electrons of other carbon atoms and this results in a tetrahedral arrangement. All of the carbon atoms in diamond lattice are sp3 hybridized.
Due to the lack of any free electrons for the charge transport, it becomes unable to conduct electricity unlike other good conductors, where free electrons are easily available for electricity.
The basic requirement for electrical conductance is the flow of electrons. Electrons are charge carriers and their flow results in the flow of charge, current. If any substance lacks free and delocalized electrons, it becomes unable to form the flow of electrons, which makes the substance a good insulator.
If a substance is rich in free electrons then it becomes easier for the electrons to flow, resulting in good electrical conductance of the substance.
Why does diamond conduct heat but not electricity?
Even though Diamond is a bad conductor of electricity, surprisingly it is a good conductor of heat. Although heat conduction and electrical conduction have a correlation because electrons passing by make it easy to conduct heat.
Most of the electrical insulators are thermal insulators as well but the same does not apply with Diamond. In the matter of Diamond, no free electrons are available to transmit current but the bound electrons in the 3-D tetrahedral structure can easily transmit energy from one covalent bond to another, and thus resulting in heat transfer.
Unlike metals, where heat is conducted by free electrons, in diamond, heat is transferred through lattice vibrations of strong covalent bonds between carbon atoms.
So, the notable difference between electrical conductance and thermal conductance is that electrical conductivity is the flow of electrons, while the thermal conductivity is the flow of energy.
The flow of electrons does contribute to better thermal conduction but it is not a necessity for transferring heat. The same strong bond between carbon atoms in diamond results in other specialties of the diamond, like hardness and optical transparency.
This high thermal conductivity of diamond is also useful in differentiating between diamond and other diamond-like substances like cubic zirconia, glass, and moissanite.
The electrical resistivity of the diamond is 100 GΩ·m. While the thermal conductivity of the diamond is 2200W/(m·K) which is about five times more than the most thermally conductive metal, Silver.
Diamonds conduct heat even better than graphite, which unlike diamond, also conducts electricity. But the benefit of transmitting energy outgrows the benefit of heat conduction due to electrical conductivity.
Why does graphite conduct electricity but not a diamond?
Graphite and Diamond both are allotropes of Carbon, yet diamond is a bad electrical conductor and graphite is a good conductor of electricity.
The reason behind good electrical conductance of graphite is the delocalization of pi bond electrons above and below the sheets of carbon atoms. Graphite has a hexagonal arrangement.
They are arranged like stacks of 2-d sheets of graphite. So this means that only three out of four outer shell electrons form a covalent bond with other carbon atoms and thus leaving one free electron.
The free electrons from all the carbon atoms are allowed to move freely among the sheets of graphene molecules. This makes graphite good conductor of electricity, unlike diamond where all of the outer shell electrons are consumed in making covalent bonds with other carbon atoms.
The funny part is that the graphite when put under high pressure and high-temperature converts into the diamond.
So, graphite and diamond even after being made of a similar element, carbon, do not share the same physical properties and the reason is merely the difference in their structure and also because the carbon atoms are bonded differently with other carbon atoms in the crystal lattice.
The electrical conductivity of graphite is 2 to 3 *10^5 while the conductivity of the diamond is as low as ~10^-13. Due to this high electrical conductivity, graphite has wide applications in electronic products such as electrodes, batteries, and solar panels.
Other allotropes of carbon like Fullerenes and other man-made carbon allotropes are also good conductors of electricity due to the availability of delocalized free electrons.
Can a diamond be doped to conduct electricity?
Yes, although natural diamonds are found to be mostly insulators, we can manipulate the physical properties of the diamond artificially. By adding boron to the lattice at higher concentrations, the diamond becomes like metals.
Boron impurities among the carbon atoms in the diamond lattice donate a hole in the valence shell. The holes stand responsible for allowing the current to flow easily.
This results in increasing the value of the electrical conductivity of the doped diamond. This transforms the diamond into a good conductor of electricity. Boron doped diamonds are very much electrically conductive and can be used in electrode materials.
The natural blue diamond is an exception among other forms of natural diamonds due to better electrical conductance.
They are not treated or enhanced artificially for the blue color, the natural blue diamond gets its color from the boron impurities which is at the same time responsible for the change in diamond’s electrical properties.
Some examples of the application of doped diamonds are phosphorus-doped diamonds films, and ultraviolet light-emitting diodes by alternating boron-doped and phosphorus-doped diamonds.
Synthetic diamonds show good potential in semiconductors and hence they are doped with boron and phosphorous impurities. The combination of both good electrical and thermal diamonds show great excitement in the applications of semiconductor in technology for the researchers.
The reason for the bad electrical conductance of diamond is the absence of free electrons which is due to its tetrahedral structure which consumes all of the electrons in a covalent bond with other carbon atoms.
The very same reason for diamond’s structure is responsible for diamond’s other great specialties like high thermal conductivity, hardness, high melting point, and optical transparency. So, the reason why diamond is not good at electrical conductance is the reason why diamond is one of the best at every other property.
Nature has its own wonderful ways to show wisdom, it gives you so much but not everything. Even the diamonds lack somewhere, pretty much like all of us.
Though we obsessively focus on achieving those things too which we are not given naturally. Even though diamond has extreme quality on all of the other properties, we stress most to master the one which is the worst one.