Gallium (Ga, atomic number 31) is a metallic conductor of electricity. This silvery-blue element is a true metal and possesses the fundamental properties required for electrical flow. French chemist Paul-Émile Lecoq de Boisbaudran discovered gallium in 1875. At standard temperature and pressure, pure gallium is a soft, slightly brittle solid. Its ability to conduct an electric current is the basis for its widespread use in modern electronics and advanced materials.
Gallium as a Metallic Conductor
Gallium’s classification as a metal explains its inherent ability to conduct electricity. It resides in Group 13 of the periodic table, alongside aluminum and indium, and exhibits characteristic metallic bonding. The atoms in solid gallium form a crystal lattice structure where their outermost valence electrons detach from individual atoms. These electrons create a “sea” of delocalized electrons that move freely throughout the metal’s structure.
When a voltage is applied across the metal, these mobile, negatively charged electrons flow toward the positive terminal, establishing an electric current. Gallium’s conductivity is generally lower than that of common conductors like copper or aluminum, but the mechanism remains the same. The presence of these free-moving electrons fundamentally defines it as a conductor, enabling efficient electrical transmission.
Conductivity and the Solid-Liquid Phase Transition
A remarkable property of gallium is its exceptionally low melting point of 29.76°C (85.57°F), meaning it can melt when held in the palm of a hand. This low melting point allows for the study of its electrical conductivity during the solid-liquid phase transition, revealing an unusual characteristic for a metal. Gallium is one of the few substances, alongside water and silicon, that expands upon freezing, meaning its solid form is less dense than its liquid form.
The electrical behavior changes significantly upon melting due to a structural reorganization. Solid gallium forms a complex, ordered orthorhombic crystal lattice, in which atoms are linked in pairs, exhibiting some covalent bonding characteristics. This specific, highly organized structure impedes the free flow of electrons, resulting in a higher electrical resistivity in the solid state. When gallium melts, the ordered crystal structure breaks down, and the liquid metal forms a less structured, more densely packed arrangement.
This transition causes a sudden decrease in electrical resistance, meaning the liquid phase is a slightly better conductor than the solid phase. For most metals, melting increases resistance because the greater atomic disorder scatters the delocalized electrons more effectively. Gallium’s unusual behavior, where the liquid is more conductive, is directly linked to the unique, less metallic, paired-atom structure of its solid form.
Essential Uses of Gallium in Electronics
Gallium’s electrical properties are leveraged not in its pure elemental form, but primarily as a component in compound semiconductors. The most significant of these are Gallium Arsenide (GaAs) and Gallium Nitride (GaN), which are foundational materials for high-performance electronics. These compounds are referred to as III-V semiconductors because they combine Gallium (Group 13) with an element from Group 15 (Arsenic or Nitrogen).
Gallium Arsenide is widely used in high-frequency applications like radio-frequency integrated circuits for cell phones and satellites due to its high electron mobility. Devices made with GaAs can operate at frequencies exceeding 250 GHz and generate less noise than traditional silicon devices. Furthermore, GaAs is a direct bandgap semiconductor, allowing it to efficiently convert electricity directly into light, which is why it is used to create solar cells, laser diodes, and infrared light-emitting diodes (LEDs).
Gallium Nitride is increasingly important in power electronics and high-brightness LEDs. GaN-based transistors can handle higher power densities and operate at higher temperatures and voltages than silicon, making them suitable for fast-charging power adapters, electric vehicle components, and high-efficiency power conversion systems.