scholarly journals Integrated structural reconstruction of unit structures of the meta-stable grain boundaries in diamond-structured materials presents first-order like phase transition.

2021 ◽  
Author(s):  
Yaoshu Xie ◽  
Kiyou Shibata ◽  
Teruyasu Mizoguchi
Keyword(s):  
Phase Transition ◽  
Grain Boundaries ◽  
Silicon Germanium ◽  
Md Simulation ◽  
Elastic Band ◽  
Structured Materials ◽  
First Order ◽  
Unit Structure ◽  
Transition Mechanism ◽  
Symmetric Tilt

Abstract One of the important issues of studying grain boundaries (GBs) which has recently attracted increasing interests is to investigate the phase behavior of GBs that one GB with determined disorientation and plane orientation (known as macroscopic parameters) can exist as distinct phases and perform phase transition. While such an issue has been investigated in fcc and bcc metals, GB phases in other elemental materials have not been reported. This work by applying molecular dynamics (MD) simulation explored totally around 7000 meta-stable GB phases of the <110>∑9(22‾1‾) symmetric tilt GB of silicon, germanium and diamond carbon as diamond-structured elemental materials. Meta-stable phases commonly exist in different elements were discovered and some of them were successfully verified to be reasonable by first-principle simulation. The verified meta-stable GBs were subsequently proved to have different capability to transform to the ground-stable GB at elevated temperature under MD simulation and to perform different pre-melting behaviors. We discovered a bi-directional structural reconstruction mechanism of the unit structure belonging to one of the verified meta-stable phases, by which the unit structures can transform to identical unit structures of the ground-stable GB which can present ‘opposite orientation’. Through computing the kinetic barriers by nudged-elastic-band and annealing simulation using MD, the integral behavior of the unit structures’ reconstruction is found to be a first-order like phase transition. Our work extended the research on GB phases from metals to diamond-structured materials and discovered a new GB phase transition mechanism which has not been reported before.

scholarly journals Monoclinic–orthorhombic first-order phase transition in K2ZnSi5O12 leucite analogue; transition mechanism and spontaneous strain analysis.

2021 ◽  
pp. 1-20
Author(s):  
Anthony M.T. Bell ◽  
Francis Clegg ◽  
Christopher M.B. Henderson
Keyword(s):  
Phase Transition ◽  
Strain Analysis ◽  
Phase Region ◽  
Martensitic Transition ◽  
Two Phase ◽  
Spontaneous Strain ◽  
First Order ◽  
Transition Mechanism ◽  
First Order Phase Transition ◽  
Increasing Temperature

Abstract Hydrothermally synthesised K2ZnSi5O12 has a polymerised framework structure with the same topology as leucite (KAlSi2O6, tetragonal I41/a), which has two tetrahedrally coordinated Al3+ cations replaced by Zn2+ and Si4+. At 293 K it has a cation-ordered framework P21/c monoclinic structure with lattice parameters a = 13.1773(2) Å, b = 13.6106(2) Å, c = 13.0248(2) Å and β = 91.6981(9)°. This structure is isostructural with K2MgSi5O12, the first cation-ordered leucite analogue characterised. With increasing temperature, the P21/c structure transforms reversibly to cation-ordered framework orthorhombic Pbca. This transition takes place over the temperature range 848−863 K where both phases coexist; there is an ~1.2% increase in unit cell volume between 843 K (P21/c) and 868 K (Pbca), characteristic of a first-order, displacive, ferroelastic phase transition. Spontaneous strain analysis defines the symmetry- and non-symmetry related changes and shows that the mechanism is weakly first order; the two-phase region is consistent with the mechanism being a strain-related martensitic transition.

Molecular Dynamic Simulation of Zigzag Silicon Carbide Nanoribbon

2021 ◽  
Vol 32 ◽  
Author(s):  
Hang Thi Thuy Nguyen
Keyword(s):  
Phase Transition ◽  
Molecular Dynamics ◽  
Silicon Carbide ◽  
Md Simulation ◽  
Structural Evolution ◽  
Order Type ◽  
Distribution Functions ◽  
Heating Process ◽  
Initial Model ◽  
First Order

The heating process of zigzag silicon carbide nanoribbon (SiCNR) is studied via molecular dynamics (MD) simulation. The initial model contained 10000 atoms is heating from 50K to 6000K to study the structural evolution of zigzag SiCNR. The melting point is defined at 4010K, the phase transition from solid to liquid exhibits the first-order type. The mechanism of structural evolution upon heating is studied based on the radiral distribution functions, coordination number, ring distributions, and angle distributions.

scholarly journals A first order phase transition mechanism underlies protein aggregation in mammalian cells

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Arjun Narayanan ◽  
Anatoli Meriin ◽  
J Owen Andrews ◽  
Jan-Hendrik Spille ◽  
Michael Y Sherman ◽  
...  
Keyword(s):  
Phase Transition ◽  
Order Phase Transition ◽  
Mammalian Cells ◽  
Normal Growth ◽  
Editorial Note ◽  
Lag Phase ◽  
First Order ◽  
Transition Mechanism ◽  
First Order Phase Transition ◽  
First Order Phase

The formation of misfolded protein aggregates is a hallmark of neurodegenerative diseases. The aggregate formation process exhibits an initial lag phase when precursor clusters spontaneously assemble. However, most experimental assays are blind to this lag phase. We develop a quantitative assay based on super-resolution imaging in fixed cells and light sheet imaging of living cells to study the early steps of aggregation in mammalian cells. We find that even under normal growth conditions mammalian cells have precursor clusters. The cluster size distribution is precisely that expected for a so-called super-saturated system in first order phase transition. This means there exists a nucleation barrier, and a critical size above which clusters grow and mature. Homeostasis is maintained through a Szilard model entailing the preferential clearance of super-critical clusters. We uncover a role for a putative chaperone (RuvBL) in this disassembly of large clusters. The results indicate early aggregates behave like condensates.Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (<xref ref-type="decision-letter" rid="SA1">see decision letter</xref>).

Isosymmetrical phase transition in α-YbV4O8

2008 ◽  
Vol 64 (6) ◽  
pp. 652-660 ◽  
Author(s):  
Karen Friese ◽  
Yasushi Kanke ◽  
Andy N. Fitch ◽  
Wolfgang Morgenroth ◽  
Andrzej Grzechnik
Keyword(s):  
Phase Transition ◽  
Three Dimensional ◽  
Structure Type ◽  
Charge Ordering ◽  
Gap Formation ◽  
Magnetic Susceptibility Data ◽  
First Order ◽  
Susceptibility Data ◽  
Transition Mechanism ◽  
Α Phase

The structure of YbV4O8 is related to the CaFe2O4 structure type. VO6 octahedra form a three-dimensional framework with tunnels in which the Yb3+ ions are incorporated. Two different polymorphs α and β are known and differ mainly in the arrangement of the Yb ions within the framework. We studied the structure and magnetic properties of α-YbV4O8 as a function of temperature. At approximately 70 K α-YbV4O8 undergoes a first-order isosymmetrical phase transition (P21/n → P21/n). While in the high-temperature α phase the three V3+ and one V4+ are disordered over the four symmetrically independent octahedral sites, in the low-temperature α′ phase complete charge ordering is observed. The transition is accompanied by a paramagnetic–paramagnetic anomaly in the magnetic susceptibility data which can be interpreted on the basis of spin-gap formation. The transition mechanism in the α polymorph is very similar to that observed earlier in the β polymorph at 185 K.

Grain Boundary Structure in ARB Processed Copper

2006 ◽  
Vol 503-504 ◽  
pp. 925-930 ◽  
Author(s):  
Kenichi Ikeda ◽  
Naoki Takata ◽  
Kousuke Yamada ◽  
Fuyuki Yoshida ◽  
Hideharu Nakashima ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Unit ◽  
Md Simulation ◽  
Boundary Structure ◽  
Dislocation Model ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Symmetric Tilt ◽  
The Difference

Grain boundary structures in the Accumulative roll-bonding (ARB) processed copper (ARB-Cu) have been studied. The grain boundary structures were observed by high-resolution transmission electron microscopy (HRTEM). In order to clarify the difference between the grain boundaries in ARB-Cu and equilibrium boundaries, calculated atomic structure of symmetric tilt grain boundaries with <110> common axis (<110> symmetric tilt grain boundary; <110> STGB) in Cu were used. The near 14° boundary in the ARB-Cu could be described by the dislocation model, but the dense dislocation region existed near the grain boundary. The high angle boundaries in ARB-Cu could be described by the structural units which were obtained by molecular dynamics (MD) simulation. Furthermore, in the 2 cycles and 6 cycles ARB-Cu (2cARB-Cu and 6cARB-Cu), the deformation twin boundaries could be observed and described by the structural unit. Therefore, it was concluded that the grain boundary structure in the ARB-Cu was not much different from the normal equilibrium grain boundary and explained by conventional dislocation and structural unit models.

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