Mapping the effects of crystal defects

New research offers insights into how crystal dislocations - a common type of defect in materials - can affect electrical and heat transport through crystals, at a microscopic, quantum mechanical level. Dislocations in crystals are places where the orderly three-dimensional structure of a crystal lattice - whose arrangement of atoms repeats with exactly the same spacing - is disrupted. The effect is as if a knife had sliced through the crystal and then the pieces were stuck back together, askew from their original positions. These defects have a strong effect on phonons, the modes of lattice vibration that play a role in the thermal and electrical properties of the crystals through which they travel. But a precise understanding of the mechanism of the dislocation-phonon interaction has been elusive and controversial, which has slowed progress toward using dislocations to tailor the thermal properties of materials. A team at MIT has been able to learn important details about how those interactions work, which could inform future efforts to develop thermoelectric devices and other electronic systems. The findings are reported in the journal Nano Letters, in a paper co-authored by postdoc Mingda Li, Department of Mechanical Engineering head Professor Gang Chen, the late Institute Professor Emerita Mildred Dresselhaus, and five others.