Thermal conductivity is a fundamental property of matter that describes how effectively a material transfers thermal energy through its structure. The standard unit of measurement is the watt per meter-Kelvin (W/m·K), which represents the power transferred per unit length and temperature difference. Leveraging high thermal conductivity materials is required for advancing modern technology. Efficient thermal energy management is crucial for maintaining performance and reliability in high-power applications where heat must be dissipated quickly.
Understanding Heat Transfer Mechanisms
The thermal conductivity of any solid material is determined by the efficiency of two primary microscopic carriers: electrons and phonons. In metals, the dominant mechanism for heat transfer is the movement of free electrons. These electrons, which also conduct electricity, transport energy rapidly through the crystal lattice structure. This connection explains why excellent electrical conductors, like silver and copper, are also excellent thermal conductors.
For non-metallic materials and electrical insulators, heat transfer relies almost entirely on lattice vibrations, quantized as particles called phonons. Phonons are waves of atomic vibration that pass energy from one atom to the next. The perfection of the crystal structure and the strength of the atomic bonds dictate how easily these phonons travel without scattering. Materials with simple, highly ordered atomic structures and strong covalent bonds, such as diamond, are highly effective at this phonon-based heat transport.
The overall thermal conductivity of a solid is the sum of the contributions from both the electronic and the phonon mechanisms. In a typical metal, the electronic component far outweighs the phonon component. Conversely, in a dielectric material, the electronic component is negligible. Impurities, structural defects, and grain boundaries within the material can disrupt the movement of electrons and phonons, significantly reducing conductivity.
The Materials with Peak Thermal Conductivity
The material with the highest theoretically measured thermal conductivity is graphene, a form of carbon. As a single layer of carbon atoms in a hexagonal lattice, graphene exhibits extraordinary in-plane thermal conductivity, with reported values reaching as high as 5300 W/m·K in suspended samples. This exceptional figure is due to its perfect two-dimensional structure and strong covalent bonds, allowing phonons to travel with minimal scattering. However, this extreme value drops significantly when the graphene is supported by a substrate or has defects.
The undisputed champion among bulk, three-dimensional materials is diamond, another carbon allotrope. High-quality natural and synthetic diamonds typically exhibit a thermal conductivity in the range of 2000 to 2200 W/m·K at room temperature. This is several times higher than that of the best metals. Diamond’s simple, tightly packed crystal structure provides an ideal pathway for phonon transport, making it the benchmark for thermal management in many high-power applications.
For materials that rely on electron transport, the noble metal silver holds the record, boasting a thermal conductivity of approximately 429 W/m·K. Copper follows closely behind with a value near 398 W/m·K. Copper is often preferred for common industrial applications due to its lower cost and similar performance. The conductivity of these metals is slightly lower than diamond because the free electrons still scatter off the lattice atoms and each other, introducing resistance to heat flow.
Essential Applications for High Conductors
The most common application for high conductors is in heat sinks and spreaders used to cool high-power electronics, such as central processing units (CPUs) and graphics processing units (GPUs). By drawing heat away from these components, these materials prevent performance degradation and failure from excessive temperature. The need for high thermal conductivity is driven by the increasing power density of integrated circuits, which generates more heat in smaller volumes.
Beyond consumer electronics, these materials are routinely utilized in advanced manufacturing and high-energy systems. High-power laser systems rely on diamond or specialized ceramics like aluminum nitride to dissipate energy and maintain precise optical alignment. In the aerospace and automotive industries, high conductors are incorporated into heat exchangers, battery packs, and engine components. Whether in the form of thin films or bulk substrates, these materials ensure that performance is not limited by thermal bottlenecks.