The stacking-fault energy (SFE) is a material property on a very small scale. It is noted as γ_SFE in units of joule

Joule

The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

s per square metre.

A stacking fault is a one or two layer interruption in the stacking sequence of the crystal structure

Crystal structure

In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...

. These interruptions carry a certain stacking fault energy. The width of stacking fault is a consequence of the balance between the repulsive force between two partial dislocation

Dislocation

In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials...

s on one hand and the attractive force due to the surface tension

Surface tension

Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 of the stacking fault on the other hand. The equilibrium width is determined by the stacking fault energy. When the SFE is high, the dissociation of a perfect dislocation into two partial is unlikely and the material deforms only by dislocation glide. Lower SFE materials display wider stacking faults and have more difficulties for cross-slip and climb.
The SFE modifies the ability of a dislocation in a crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

 to glide onto an intersecting slip plane

Slip (materials science)

In materials science, Slip is the process by which plastic deformation is produced by a dislocation motion. By an external force, parts of the crystal lattice glide along each other, resulting in a changed geometry of the material. Depending on the type of lattice, different slip systems are...

. When the SFE is low, the mobility of dislocations in a material decreases.

Material	Ag (Silver Silver Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal... )	Ni (Nickel Nickel Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile... )	Mg (Magnesium Magnesium Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole... )	Al (Aluminum)
SFE (mJ m-2)	20	90	125	160-200