Prediction of site occupancy of C15 Laves phase at finite temperature based on quasi-harmonic approximation model

2018 ◽  
Vol 96 ◽  
pp. 33-40 ◽  
Author(s):  
Zhenyi Wei ◽  
Yixu Yang ◽  
Jinchang Huang ◽  
Bo Wu ◽  
Baisheng Sa ◽  
...  
Keyword(s):  
Finite Temperature ◽  
Harmonic Approximation ◽  
Site Occupancy ◽  
Laves Phase ◽  
Approximation Model

A Finite-Temperature Continuum Theory Based on Interatomic Potentials

2005 ◽  
Vol 127 (4) ◽  
pp. 408-416 ◽  
Author(s):  
H. Jiang ◽  
Y. Huang ◽  
K. C. Hwang
Keyword(s):  
Temperature Dependence ◽  
Finite Temperature ◽  
Interatomic Potential ◽  
Coefficient Of Thermal Expansion ◽  
Harmonic Approximation ◽  
Continuum Theory ◽  
Single Wall Carbon Nanotubes ◽  
Interatomic Potentials ◽  
Atomistic Models ◽  
Continuum Theories

There are significant efforts to develop continuum theories based on atomistic models. These atomistic-based continuum theories are limited to zero temperature (T=0K). We have developed a finite-temperature continuum theory based on interatomic potentials. The effect of finite temperature is accounted for via the local harmonic approximation, which relates the entropy to the vibration frequencies of the system, and the latter are determined from the interatomic potential. The focus of this theory is to establish the continuum constitutive model in terms of the interatomic potential and temperature. We have studied the temperature dependence of specific heat and coefficient of thermal expansion of graphene and diamond, and have found good agreements with the experimental data without any parameter fitting. We have also studied the temperature dependence of Young’s modulus and bifurcation strain of single-wall carbon nanotubes.

Pressure effect on the structural, phonon, elastic and thermodynamic properties of L12phase RH3TA: First-principles calculations

2018 ◽  
Vol 32 (14) ◽  
pp. 1850169
Author(s):  
Leini Wang ◽  
Zhang Jian ◽  
Wei Ning
Keyword(s):  
Thermodynamic Properties ◽  
Density Functional ◽  
Harmonic Approximation ◽  
Debye Model ◽  
Approximation Model ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Relationship Of ◽  
G Ratio ◽  
Wide Pressure

The phonon, elastic and thermodynamic properties of L12phase Rh3Ta have been investigated by the density functional theory (DFT) approach combined with the quasi-harmonic approximation model. The results of the phonon band structure show that L12phase Rh3Ta possesses dynamical stability in the pressure range from 0–80 GPa due to the absence of imaginary frequencies. The pressure dependences with the elastic constants C[Formula: see text], shear modulus G, bulk modulus B, Young’s modulus Y, Poisson’s ratio and B/G ratio have been analyzed. The results of the elastic properties studies show that L12phase Rh3Ta compound is mechanically stable and possesses a higher hardness, improved ductility and plasticity under higher pressures. The pressure and temperature relationship of the thermodynamic properties, such as the Debye temperature [Formula: see text], heat capacity C[Formula: see text], thermal expansion coefficient [Formula: see text] and the Grüneisen parameter [Formula: see text] are predicted by the quasi-harmonic Debye model in a wide pressure (0–80 GPa) and temperature (0–750 K) ranges.

Ternary transition metal gallides with TiNiSi, ZrBeSi and MgZn2-type structure

2019 ◽  
Vol 74 (3) ◽  
pp. 297-306 ◽  
Author(s):  
Lukas Heletta ◽  
Theresa Block ◽  
Steffen Klenner ◽  
Rainer Pöttgen
Keyword(s):  
Transition Metal ◽  
Powder Diffraction ◽  
Metallic Iron ◽  
Site Occupancy ◽  
Laves Phase ◽  
Structural Motif ◽  
Equiatomic Composition ◽  
Laves Phases ◽  
X Ray ◽  
Arc Melting

AbstractA series of ternary transition metal gallides around the equiatomic composition have been synthesized from the elements by arc-melting and subsequent annealing. The compounds crystallize with site occupancy variants of the hexagonal Laves phase MgZn2, with the hexagonal ZrBeSi or the orthorhombic TiNiSi type. All samples have been characterized on the basis of their lattice parameters, determined by X-ray powder diffraction (Guinier technique). The structures of NbCr1.58Ga0.42 and NbFe1.51Ga0.49 (MgZn2 type, P63/mmc), NbRhGa (ZrBeSi type, P63/mmc), and ScNiGa, ScPtGa and ScAuGa (TiNiSi type, Pnma) were refined from single crystal X-ray diffractometer data. The ScPtGa and ScAuGa crystals showed trilling formation. Mixed site occupancies were only observed in the Laves phases while all other crystals were well ordered. A striking structural motif of NbRhGa is the formation of niobium chains (264 pm Nb–Nb) along the c axis. Several gallides were magnetically characterized. They are Pauli paramagnets. The two crystallographically independent iron sites in the Laves phase TaFeGa could be distinguished in the 57Fe Mössbauer spectrum. The isomer shifts of 0.06(3) (Fe1) and –0.02(3) (Fe2) mm s−1 indicate metallic iron.

FINITE TEMPERATURE RESULTS FROM CONSTRAINED FERMIONIZATION IN THE 2-D SPIN 1/2 HEISENBERG ANTIFERROMAGNET II: FLUCTUATIONS IN THE DIMER PHASES

1994 ◽  
Vol 08 (06) ◽  
pp. 757-776 ◽  
Author(s):  
M. DI STASIO ◽  
A. TAGLIACOZZO ◽  
E. ERCOLESSI ◽  
G. MORANDI
Keyword(s):  
Saddle Point ◽  
Specific Heat ◽  
Finite Temperature ◽  
Site Occupancy ◽  
Zero Point ◽  
Single Site ◽  
Heisenberg Antiferromagnet ◽  
Zero Point Energy ◽  
Saddle Point Approximation ◽  
Point Energy

The constraint of single-site occupancy is implemented in the fermionization of the model, within the saddle point approximation. The columnar and the staggered dimer phases are studied and the contribution of the fluctuations to the zero point energy and the specific heat is analyzed.

FINITE TEMPERATURE RESULTS FROM CONSTRAINED FERMIONIZATION IN THE 2-D SPIN 1/2 HEISENBERG ANTIFERROMAGNET I: THE NÉEL PHASE

1994 ◽  
Vol 08 (06) ◽  
pp. 741-756 ◽  
Author(s):  
M. DI STASIO ◽  
A. TAGLIACOZZO ◽  
E. ERCOLESSI ◽  
G. MORANDI
Keyword(s):  
Saddle Point ◽  
Specific Heat ◽  
Spin Wave ◽  
Finite Temperature ◽  
Wave Spectrum ◽  
Site Occupancy ◽  
Zero Point ◽  
Wave Theory ◽  
Heisenberg Antiferromagnet ◽  
Spin Wave Spectrum

The antiferromagnetic saddle point is studied up to one-loop corrections, including, within the same approximation, the constraint of single site occupancy in the fermionization procedure, at all temperatures. The resulting spin wave spectrum and zero point fluctuations are the same as those of the spin wave theory. The effect of the constraint on the temperature dependence of the specific heat is discussed.

Unstable Stacking Fault Free Energies in Silicon through Empirical Modeling

1998 ◽  
Vol 539 ◽  
Author(s):  
M. De Koning ◽  
A. Antonelli ◽  
Martin Z. Bazant ◽  
Efthimios Kaxiras ◽  
J.F. Justo
Keyword(s):  
Finite Temperature ◽  
Transition State Theory ◽  
Harmonic Approximation ◽  
State Theory ◽  
Dislocation Nucleation ◽  
Stacking Fault ◽  
Empirical Modeling ◽  
Zero Temperature ◽  
Free Energies ◽  
Brittle Ductile Transition

AbstractThe temperature dependence of unstable stacking fault free energies on glide and shuffle {111} planes in silicon is investigated using a finite temperature molecular dynamics approach which includes a full treatment of anharmonic vibrational effects. The results are compared to earlier zero temperature ab initio calculations in which finite temperature effects were estimated using a harmonic approximation to transition state theory (TST). The unstable stacking free energies are interpreted within the framework of Rice‘s dislocation nucleation criterium to characterize a possible change from shuffle to glide plane dominance in the context of dislocation nucleation processes at a sharp crack tip. Such a change may be related to the abrupt brittle-ductile transition observed in silicon.

A Finite Temperature Multiscale Interphase Zone Model and Simulations of Fracture

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Lisheng Liu ◽  
Shaofan Li
Keyword(s):  
Finite Element ◽  
Finite Temperature ◽  
Thermal Conduction ◽  
Colloidal Crystal ◽  
Constitutive Relations ◽  
Harmonic Approximation ◽  
Zone Model ◽  
Element Formulation ◽  
Material Interface ◽  
Finite Element Procedure

In this work, an atomistic-based finite temperature multiscale interphase finite element method has been developed, and it has been applied to study fracture process of metallic materials at finite temperature. The coupled thermomechanical finite element formulation is derived based on continuum thermodynamics principles. The mesoscale constitutive relations and thermal conduction properties of materials are enriched by atomistic information of the underneath lattice microstructure in both bulk elements and interphase cohesive zone. This is accomplished by employing the Cauchy–Born rule, harmonic approximation, and colloidal crystal approximation. A main advantage of the proposed approach is its ability to capture the thermal conduction inside the material interface. The multiscale finite element procedure is performed to simulate an engineering nickel plate specimen with weak interfaces under uni-axial stretch. The simulation results indicate that the crack propagation is slowed down by thermal expansion, and a cooling region is found in the front of crack tip. These phenomena agree with related experimental results. The effect of different loading rates on fracture is also investigated.

scholarly journals Site Occupancies in Ternary C15 Ordered Laves Phases

1996 ◽  
Vol 460 ◽  
Author(s):  
P. G. Kotula ◽  
I. M. Anderson ◽  
F. Chu ◽  
D. J. Thoma ◽  
J. Bentley ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Total Energy ◽  
Phase Diagrams ◽  
First Principles ◽  
Site Occupancy ◽  
Electronic Structure Calculations ◽  
Laves Phase ◽  
Laves Phases ◽  
Structure Calculations

ABSTRACTSite occupancies in three C15-structured AB2(X) Laves phases have been determined with Atom Location by CHanneling Enhanced MIcroanalysis (ALCHEMI). In NbCr2(V), the results are consistent with exclusive site occupancies of Nb for the A sublattice and Cr and V for the A sublattice. The B-site occupancy of V can be interpreted in terms of electronic structure. In NbCr2(Ti), the results are consistent with Ti partitioning mostly to the A sites with some anti-site defects likely. In HfV2(Nb), the results are consistent with Nb partitioning between the A and A sites. The results of the ALCHEMI analyses of these ternary C15 Laves phase materials are discussed with respect to previously determined phase diagrams and first-principles total energy and electronic structure calculations.

scholarly journals High-throughput prediction of finite-temperature properties using the quasi-harmonic approximation

2016 ◽  
Vol 125 ◽  
pp. 82-91 ◽  
Author(s):  
Pinku Nath ◽  
Jose J. Plata ◽  
Demet Usanmaz ◽  
Rabih Al Rahal Al Orabi ◽  
Marco Fornari ◽  
...  
Keyword(s):  
High Throughput ◽  
Finite Temperature ◽  
Harmonic Approximation
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