Beatrice Lang
Electrical conductors are materials that allow electricity to flow through them easily. The property of conductors to conduct electricity is called conductivity. Materials with good mobility of electrons are known as conductors, and materials with less mobility of electrons are referred to as insulators. The best electrical conductor, under conditions of ordinary temperature and pressure, is the metallic element silver. However, silver is rarely used in residential or commercial settings due to its high cost and susceptibility to tarnishing. Other good electrical conductors include copper, gold, aluminium, steel, brass, and graphite.
| Characteristics | Values |
|---|---|
| Materials | Metals, electrolytes, superconductors, semiconductors, plasmas, non-metallic conductors (e.g., graphite, conductive polymers), ionic solutions |
| Material properties | Loosely bound electrons, free movement of electrons, good electron mobility |
| Examples | Copper, iron, gold, aluminum, silver, brass, steel, hydrogen, mercury |
| Applications | Wiring, machinery, appliances, sensors, communication systems, renewable energy systems, medical equipment, aerospace equipment, power transmission |
| Factors affecting conductivity | Temperature, material composition, impurities, defects, crystal structure, geometry, size |
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Metals
Silver is the best electrical conductor under ordinary temperature and pressure conditions. However, silver is rarely used in residential or commercial settings due to its rarity and high cost. Silver is also prone to tarnishing, and the oxide layer known as tarnish is not conductive.
Copper is another excellent electrical conductor. It is the international standard to which other electrical conductors are compared. Copper is also highly flexible, making it ideal for electrical connectors and wiring that must withstand significant electrical loads.
Other good metal conductors include gold, aluminium, iron, brass, and steel. Aluminium is the most common metal in electric power transmission and distribution due to its low density, which makes it twice as conductive by mass as copper. However, aluminium has some disadvantages, such as its tendency to form an insulating oxide and its higher coefficient of thermal expansion, which can loosen connections.
The conductivity of metals can be affected by various factors, including temperature, material composition, impurities and defects, and crystal structure. As the temperature of a conductive metal increases, the thermal vibrations of atoms also increase, impacting the movement of electrons and reducing conductivity. Therefore, most metals are better conductors when cool and less efficient when hot.
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Electrolytes
Electrolyte solutions can result from the dissolution of some biological or synthetic polymers, termed "polyelectrolytes", which contain charged functional groups. A substance that dissociates into ions in solution or in the melt acquires the ability to conduct electricity. Sodium, potassium, chloride, calcium, magnesium, and phosphate in a liquid phase are examples of electrolytes. In medicine, electrolyte replacement is needed when a person has prolonged vomiting or diarrhea, and in response to sweating due to strenuous athletic activity.
The strength of an electrolyte is determined by its ability to form ions. Strong electrolytes form ions easily, while weak electrolytes do not form ions easily. For example, potassium nitrate is a strong electrolyte, while acetic acid is a weak electrolyte. The concentration of ions in a solution will also affect its conductivity. The larger the concentration of ions, the better the solution conducts.
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Superconductors
Electrical conductors are materials that allow the flow of electric charge or current. Metals are common electrical conductors, with electrons acting as the primary movers. Other conductors include cationic electrolytes, superconductors, semiconductors, plasmas, and some non-metallic conductors like graphite and conductive polymers.
The phenomenon of superconductivity was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes, who found that the electrical resistance of a mercury wire disappeared when it was cooled below approximately 4 Kelvin (-269 degrees Celsius). This critical temperature depends on the isotopic mass of the constituent element.
A superconductor can be returned to its normal, non-superconducting state by passing a large current through it or applying a strong magnet. The lack of electrical resistance in superconducting wires allows them to support very high electrical currents. However, above a "critical current," the electron pairs that enable superconductivity break up, and superconductivity is lost.
The Meissner effect, discovered by Meissner and Ochsenfeld in 1933, is a defining characteristic of superconductivity. It describes the expulsion of applied magnetic fields from superconductors, a phenomenon that is very strong in these materials. Fritz and Heinz London further contributed to the understanding of the Meissner effect by showing that it resulted from the minimization of electromagnetic free energy carried by the superconducting current.
The BCS theory, proposed by Bardeen, Cooper, and Schrieffer in 1957, explains the superconducting current as a superfluid of Cooper pairs, which are pairs of electrons interacting through the exchange of phonons or atomic-level vibrations. This theory was strengthened in 1958 by N. N. Bogolyubov, who demonstrated that the BCS wavefunction could be obtained using a canonical transformation of the electronic Hamiltonian.
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Semiconductors
Materials are classified as conductors, insulators, or semiconductors based on their electric conductivity. Semiconductors are defined by their unique electric conductive behaviour, which falls somewhere between that of a conductor and an insulator. In their natural state, semiconductors are poor conductors because a current requires the flow of electrons, and semiconductors have their valence bands filled, preventing the flow of new electrons.
However, several developed techniques allow semiconducting materials to behave like conducting materials, such as doping or gating. These modifications have two outcomes: n-type and p-type, referring to the excess or shortage of electrons, respectively. The addition of about 10 atoms of boron (known as a dopant) per million atoms of silicon, for example, can increase its electrical conductivity a thousandfold.
The differences between these materials can be understood in terms of the quantum states for electrons, each of which may contain zero or one electron (by the Pauli exclusion principle). These states are associated with the electronic band structure of the material. Electrical conductivity arises due to the presence of electrons in states that are delocalized (extending through the material). However, in order to transport electrons, a state must be partially filled, containing an electron only part of the time. If the state is always occupied by an electron, it is inert, blocking the passage of other electrons via that state.
The energies of these quantum states are critical since a state is partially filled only if its energy is near the Fermi level. High conductivity in material comes from it having many partially filled states and much state delocalization. Metals are good electrical conductors and have many partially filled states with energies near their Fermi level. Insulators, by contrast, have few partially filled states, and their Fermi levels sit within band gaps with few energy states to occupy.
The highest energy band occupied by electrons is the valence band. In a conductor, the valence band is partially filled, and since there are numerous empty levels, the electrons are free to move under the influence of an electric field. In an insulator, electrons completely fill the valence band, and the gap between it and the next band, the conduction band, is large. The electrons cannot move under the influence of an electric field unless they are given enough energy to cross the large energy gap to the conduction band. In a semiconductor, the gap to the conduction band is smaller than in an insulator. At room temperature, the valence band is almost completely filled, with a few electrons missing since they have acquired enough thermal energy to cross the band gap to the conduction band; as a result, they can move under the influence of an external electric field.
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Non-metallic conductors
While metals are the most common electrical conductors, there are some non-metallic conductors as well. These include graphite and conductive polymers, electrolytes, superconductors, and semiconductors.
Graphite, a form of carbon, is a non-metallic conductor often used in lubricants and as a refractory material. It has a layered structure that allows electrons to move freely, giving it metallic properties. Conductive polymers are another type of non-metallic conductor that have been developed to replace metals in certain applications. These polymers are made from long chains of carbon atoms and can be flexible, lightweight, and moulded into different shapes, making them useful for a variety of applications such as anti-static coatings and electrical components.
Electrolytes, which are commonly found in batteries, are another type of non-metallic conductor. They work by allowing the flow of charged ions through a bulk lattice structure, driven by an electric field. Superconductors, such as certain ceramics, can also be non-metallic. These materials offer zero resistance to the flow of electric current, but only under extremely low temperatures.
Semiconductors are materials that have a conductivity between that of conductors and insulators. They are unique in that their conductivity can be altered by introducing impurities or doping them with other elements. This makes them extremely useful in electronic devices such as transistors and diodes. It's worth noting that while most non-metallic conductors exist, they typically offer higher resistance to the flow of electric current compared to metallic conductors.
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Frequently asked questions
Electrical conductors are materials that allow electricity to flow through them easily.
Metals are the most common electrical conductors. Some of the best metal conductors are silver, copper, gold, aluminium, iron, brass, and steel. There are also non-metallic conductors, such as graphite, conductive polymers, and saltwater.
As the temperature of a conductive metal increases, so do the thermal vibrations of its atoms, impacting the movement of electrons and reducing its conductivity. Some insulators, like glass, are poor conductors when cool but become good conductors when hot.
