Researchers at the Massachusetts Institute of Technology (MIT) have provided useful insights into how crystal dislocations, disruptions in the three-dimensional structure of a crystal lattice, affect electrical and heat transport at a microscopic, quantum mechanical level, according to a report from the school’s website.
MIT researchers examined the impact of dislocations affected phonons. (MIT)
Crystal dislocations interact with phonons, which play a role in the thermal and electrical properties of the crystals, but prior to this research there was no consensus on how that interaction played out.
“Now, the MIT team has found a new mathematical approach to analyzing such systems, using a new quasiparticle they formulated called a ‘dislon,’ which is a quantized version of a dislocation, which seems to resolve these longstanding mysteries,” the article explained.
This new theory sets the parameters for the discussion of dislocation-phonon interactions and is based on quantum field theory. According to the MIT scientists, the competing theories of dynamic and static scattering both fit within the same framework, only on extreme ends of the spectrum.
The new theory accounts for the long-range nature of the dislocation strain field by creating a new quantum mechanical object, which they refer to as a dislon.
According to a Northwestern University professor who was quoted in the MIT article, “Combining this with the quantum mechanical treatment of the dislon-electron interaction could lead to new strategies to optimize materials by using metallurgical approaches to engineer the structure, type, and location of dislocations within a material.”
The researchers believe that this breakthrough could lead to more efficient thermoelectric materials that convert heat into electricity.
The work was recently published in Nano Letters. The abstract from the report stated:
“Despite the long history of dislocation–phonon interaction studies, there are many problems that have not been fully resolved during this development. These include an incompatibility between a perturbative approach and the long-range nature of a dislocation, the relation between static and dynamic scattering, and their capability of dealing with thermal transport phenomena for bulk material only.
“Here by utilizing a fully quantized dislocation field, which we called a “dislon”, a phonon interacting with a dislocation is renormalized as a quasi-phonon, with shifted quasi-phonon energy, and accompanied by a finite quasi-phonon lifetime, which are reducible to classical results. A series of outstanding legacy issues including those above can be directly explained within this unified phonon renormalization approach.
“For instance, a renormalized phonon naturally resolves the decade-long debate between dynamic and static dislocation–phonon scattering approaches, as two limiting cases. In particular, at nanoscale, both the dynamic and static approaches break down, while the present renormalization approach remains valid by capturing the size effect, showing good agreement with lattice dynamics simulations.”