College of Engineering News • Iowa State University

Team from Aerospace Engineering, Materials Science and Engineering, Ames Lab finds criterion to predict phase transformations under general stresses

A research team consisting of four scientists: Nikolai A. Zarkevich, researcher with the U.S. Department of Energy Ames Laboratory; Hao Chen, an Aerospace Engineering graduate student; Valery Levitas, Anson Marston Distinguished Professor and Vance Coffman Faculty Chair Professor in Aerospace Engineering; and Duane D. Johnson, F. Wendell Miller Professor in Materials Science and Engineering, has had its first published work released.

“Lattice Instability during Solid-Solid Structural Transformations under a General Applied Stress Tensor: Example of Si I → Si II with Metallization” (click here) has been published in Physical Review Letters, a highly ranked physics journal.

Research graphicThe paper employs the density functional theory to study the stress-strain behavior and elastic crystal lattice instabilities during the solid-solid phase transformation when subjected to all six components of stress tensor. This was seen to be impossible, due to the large number of combinations. However, the research team found unexpected guidance from the crystal lattice instability criterion analytically formulated within the phase-field method.

Atomistic simulations showed very good correspondence with this analytical criterion for more than 10,000 different stress states. Surprisingly, the phase transformation criterion has just two material parameters. Hence, it can be determined by atomistic calculations for just two different stress states.

A very strong effect of non-hydrostatic stresses was found. Thus, under hydrostatic conditions phase transformation occurs at 76 GPa, while under uniaxial loading pressure is 21 times lower. The theoretical work reveals novel, more practical synthesis routes for new or known high-pressure phases under predictable non-hydrostatic loading.

Physical Review Letters is the world’s premier physics journal and the American Physical Society’s flagship publication.

Nikolai Zarkovich
Nikolai Zarkevich, Ames Laboratory
Hao Chen
Aerospace Engineering graduate student Hao Chen
Valery Levitas
Anson Marston Distinguished Professor Valery Levitas
Duane Johnson
F. Wendell Miller Professor in Materials Science and Engineering Duane Johnson