19 research outputs found
Effect of Interfacial Structural Phase Transitions on the Coupled Motion of Grain Boundaries: A Molecular Dynamics Study
In this work the coupled motion of two different phases of
{\Sigma}5(210)[001] grain boundaries were investigated by molecular dynamics
simulations of fcc Cu. The effect of interfacial structural phase transitions
is shown to have a profound effect on both the shear strength and the nature of
the coupled motion. Specifically, the motion of the two different phases is
described by ideal coupling factors {\beta} and {\beta} that have
different magnitudes and even signs. Additionally, the shear strength for the
two inter- facial phases is observed to differ by up to 40 % at the lowest
temperatures simulated. The study demonstrates that grain boundary phases
transitions may have strong effects on the kinetics of microstructural
evolution.Comment: 8 pages, 4 figure
Structural phase transformations in metallic grain boundaries
Structural transformations at interfaces are of profound fundamental interest
as complex examples of phase transitions in low-dimensional systems. Despite
decades of extensive research, no compelling evidence exists for structural
transformations in high-angle grain boundaries in elemental systems. Here we
show that the critical impediment to observations of such phase transformations
in atomistic modeling has been rooted in inadequate simulation methodology. The
proposed new methodology allows variations in atomic density inside the grain
boundary and reveals multiple grain boundary phases with different atomic
structures. Reversible first-order transformations between such phases are
observed by varying temperature or injecting point defects into the boundary
region. Due to the presence of multiple metastable phases, grain boundaries can
absorb significant amounts of point defects created inside the material by
processes such as irradiation. We propose a novel mechanism of radiation damage
healing in metals which may guide further improvements in radiation resistance
of metallic materials through grain boundary engineering.Comment: 25 pages, 11 figure
Structures and transitions in bcc tungsten grain boundaries and their role in the absorption of point defects
We use atomistic simulations to investigate grain boundary (GB) phase
transitions in el- emental body-centered cubic (bcc) metal tungsten. Motivated
by recent modeling study of grain boundary phase transitions in [100] symmetric
tilt boundaries in face-centered cu- bic (fcc) copper, we perform a systematic
investigation of [100] and [110] symmetric tilt high-angle and low-angle
boundaries in bcc tungsten. The structures of these boundaries have been
investigated previously by atomistic simulations in several different bcc
metals including tungsten using the the {\gamma}-surface method, which has
limitations. In this work we use a recently developed computational tool based
on the USPEX structure prediction code to perform an evolutionary grand
canonical search of GB structure at 0 K. For high-angle [100] tilt boundaries
the ground states generated by the evolutionary algorithm agree with the
predictions of the {\gamma}-surface method. For the [110] tilt boundaries, the
search predicts novel high-density low-energy grain boundary structures and
multiple grain boundary phases within the entire misorientation range.
Molecular dynamics simulation demonstrate that the new structures are more
stable at high temperature. We observe first-order grain boundary phase
transitions and investigate how the structural multiplicity affects the
mechanisms of the point defect absorption. Specifically, we demonstrate a
two-step nucleation process, when initially the point defects are absorbed
through a formation of a metastable GB structure with higher density, followed
by a transformation of this structure into a GB interstitial loop or a
different GB phase.Comment: 40 pages, 19 figure
Computational Design of Flexible Electride with Nontrivial Band Topology
Electrides, with their excess electrons distributed in crystal cavities playing the role of anions, exhibit a variety of unique electronic and magnetic properties. In this work, we employ the first-principles crystal structure prediction to identify a new prototype of A3B electride in which both interlayer spacings and intralayer vacancies provide channels to accommodate the excess electrons in the crystal. This A3B type of structure is calculated to be thermodynamically stable for two alkaline metals oxides (Rb3O and K3O). Remarkably, the unique feature of multiple types of cavities makes the spatial arrangement of anionic electrons highly flexible via elastic strain engineering and chemical substitution, in contrast to the previously reported electrides characterized by a single topology of interstitial electrons. More importantly, our first-principles calculations reveal that Rb3O is a topological Dirac nodal line semimetal, which is induced by the band inversion at the general electronic k momentums in the Brillouin zone associated with the intersitial electric charges. The discovery of flexible electride in combining with topological electronic properties opens an avenue for electride design and shows great promises in electronic device applications