Classification of Electrical Engineering Materials

Materials used in Electrical Engineering are called Electrical Engineering materials. Engineers classify them by the property that controls an application, such as electrical conductivity, dielectric strength or magnetic response. One material can belong to more than one functional class, so final selection also considers temperature, frequency, mechanical stress, environment and cost.

1. Conductors
2. Semiconductors
3. Insulators
4. Magnetic material

The figure below gives a high-level classification of these electrical engineering materials.

Conductors

Conductors have high electrical conductivity and low resistivity because mobile charge carriers respond readily to an electric field. In metals, conduction electrons move through the crystal lattice.
Examples: Silver, copper, gold and aluminium.
At about room temperature, silver has slightly higher conductivity than copper. Copper and aluminium are widely used because engineers must balance conductivity with cost, mass, strength, corrosion resistance and connection method when selecting conductors.

Semiconductors

Semiconductors have conductivity between typical conductors and insulators, and their carrier concentration can be changed by doping, temperature and light. Silicon and germanium are elemental group-IV materials; compounds include III-V materials such as gallium arsenide and II-VI materials such as zinc sulfide. Many use covalent bonding. The conductivity of semiconductors can vary by orders of magnitude. Intrinsic carrier concentration increases strongly with temperature, while doped materials have different temperature regions.
Example: Germanium, Silicon and gallium arsenide.

Insulating Materials

Insulating materials have low conductivity and high resistivity. They limit leakage between current-carrying parts and grounded structures. Their electrons are not readily available for conduction, but no practical insulator is perfect. Engineers select insulating materials by dielectric strength, leakage, temperature rating, frequency, moisture resistance, mechanical strength and ageing behaviour; an excessive electric field can cause breakdown.
Example:- Plastics, ceramics, PVC, glass, paper, oil and air.

Magnetic Materials

Magnetic response affects cores, inductors, transformers, motors and generators. High-permeability core materials can provide a low-reluctance path for magnetic flux, but useful selection also depends on saturation, hysteresis, electrical resistivity, frequency and temperature. The categories below describe susceptibility and magnetic ordering, except ferrites, which are a family of ceramic materials that are usually ferrimagnetic.

• Ferromagnetic materials
• Paramagnetic material
• Diamagnetic materials
• Antiferromagnetic materials
• Ferrites

Ferromagnetic Materials

Ferromagnetic materials have a large positive magnetic response below their Curie temperature. Domains can align strongly with an external magnetic field. Their magnetisation follows a hysteresis loop as the field cycles, and materials with sufficient remanence and coercivity retain magnetisation after the field is removed.
Example: Iron, cobalt and nickel.

Paramagnetic Material

Paramagnetic materials have a small positive susceptibility. An external field gives them a weak magnetisation in the field direction, but they do not retain it when the field is removed. Examples include aluminium, platinum and oxygen; air is weakly paramagnetic because it contains oxygen.

Diamagnetic materials

Diamagnetic materials have a small negative magnetic susceptibility. An applied field induces magnetisation in the opposite direction, so the material is weakly repelled and has no remanent magnetisation after the field is removed. Diamagnetism exists in all matter but can be masked by stronger magnetic responses. Silver, copper, gold and bismuth are diamagnetic examples.

Antiferromagnetic materials

Below the Néel temperature, magnetic moments in an antiferromagnetic material order in opposite directions so their net magnetisation is usually close to zero. Above that temperature, the material becomes paramagnetic. An external magnetic field normally produces only a small response, although canted or imperfect structures can have a small net moment.
Example: Chromium, MnO, FeO, CoO and NiO.

Ferrites

Ferrites are ceramic compounds based on iron oxide. Most are ferrimagnetic: opposing magnetic sublattices have unequal moments, leaving a net magnetisation. Compared with metallic ferromagnetic materials, ferrites usually have much higher electrical resistivity, which can reduce eddy-current loss at high frequency. Many metallic ferromagnetic materials have higher magnetic saturation than ferrites, so core selection must balance frequency, flux density, loss and temperature.
Example: Fe₃O₄ and BaO.6Fe₂O₃.