interlayer

An interlayer is a layer positioned between two other layers within a stratified or layered system. It often acts as a spacer, a barrier, an adhesive interface, or a functional region that mediates interactions between neighboring layers.

In materials science and crystallography, interlayers are central to many layered materials such as graphite, mica, and clay minerals. The weak bonding between adjacent layers allows expansion, intercalation of ions or molecules, or solvent uptake. The distance between layers, known as the interlayer spacing or d-spacing, is a key parameter that influences mechanical strength, electrical or ionic conductivity, and diffusion properties. Techniques such as X-ray diffraction are used to measure interlayer spacing, and processes like intercalation or exfoliation are used to tailor interlayer properties. Examples include lithium intercalation in graphite for batteries and water-induced swelling of clays.

In electronics and coatings, an interlayer refers to a layer placed between two functional layers, such as interlayer dielectrics in integrated circuits or diffusion- or adhesion-promoting layers that improve bonding and prevent unwanted species from crossing interfaces.

In geology and sedimentology, interlayers are thin, distinct layers within rocks or sediments that reflect changes in depositional conditions, diagenesis, or organic content. They can influence the interpretation of formation histories and fluid flow in basins.

Characterization of interlayers often involves X-ray diffraction, electron microscopy, spectroscopy, and mechanical testing, with applications ranging from energy storage and coatings to lubrication and composites.