Pressure induced wurtzite-to-zinc blende phase transition in ZnO at finite temperature

2008 ◽  
Vol 23 (12) ◽  
pp. 3347-3352 ◽  
Author(s):  
Yaping Wu ◽  
Junyong Kang ◽  
Feng Liu
Keyword(s):  
Phase Transition ◽  
Energy Barrier ◽  
Energy Difference ◽  
Vibrational Entropy ◽  
Free Energies ◽  
Zinc Blende ◽  
Face Centered ◽  
Two Phases ◽  
Dynamics Simulations ◽  
Increasing Temperature

We predict a possible phase transition of ZnO from wurtzite to zinc blende structure using first-principles molecular-dynamics simulations. By calculating the Gibbs free energies of the two phases as a function of temperature and hydrostatic pressure, we show that their energy difference decreases continuously with increasing temperature and pressure, and the vibrational entropy plays an important role on the location of the phase transition point. At 300 K, the phase transition is expected to occur at a pressure lower than 30 GPa with an activation energy barrier of 0.386 eV/atom. The transition path was also simulated, along which the system goes through a transient face-centered orthorhombic structure to overcome the energy barrier. Our theory results may be valuable for stabilizating the zinc blende ZnO in experiment.

On reconstitutive phase transitions and the jump of the chemical potential

Analysis ◽  
2008 ◽  
Vol 28 (1) ◽  
Author(s):  
Thomas Blesgen
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Weak Solutions ◽  
Transition Layer ◽  
Chemical Potential ◽  
Sharp Interface ◽  
Free Energies ◽  
Diffusion In Solids ◽  
Existence Of Weak Solutions ◽  
Two Phases

This article studies diffusion in solids in the case of two phases under isothermal conditions where due to plastic effects the number of vacancies changes when crossing a transition layer, i.e. a reconstitutive phase transition. A segregation model is derived and the equations are studied in the limit of a sharp interface. A Gibbs–Thomson law is derived and it is shown that the vacancy component of the chemical potential jumps across the transition layer thereby explaining recent experimental observations. The thermodynamic correctness of the model is shown as well as the existence of weak solutions with logarithmic free energies.

ELASTIC AND VIBRATIONAL PROPERTIES OF ORDERED AND DISORDERED CuMnPt6

2013 ◽  
Vol 27 (27) ◽  
pp. 1350195 ◽  
Author(s):  
SHUO HUANG ◽  
CHUAN-HUI ZHANG ◽  
JING SUN ◽  
JIANG SHEN
Keyword(s):  
Elastic Anisotropy ◽  
Point Of View ◽  
Vibrational Properties ◽  
Face Centered Cubic ◽  
Vibrational Entropy ◽  
Embedded Atom ◽  
Face Centered ◽  
Two Phases ◽  
Fcc Phase ◽  
Experimental Values

In this paper, we have measured the elastic and vibrational properties of CuMnPt 6 with embedded-atom method in three states of chemical order: as a disordered FCC (face-centered cubic) solid solution and as the equilibrium L1 2 and ABC 6 ordered structures. Our results agree quite well with the comparable experimental values. The present calculations indicate that the ABC 6 and L1 2 phases are energetically more stable than FCC phase. Numerical estimates of a set of elastic parameters, including aggregate elastic modulus, Poisson's ratio, and elastic anisotropy are performed, and the results demonstrate that the FCC phase is much softer than other two phases. Further analysis from the point of view of vibrational properties such as phonon density of states and vibrational entropy difference are also presented in this study.

Phase transition and dislocation nucleation in Cu–Nb layered composites during physical vapor deposition

2008 ◽  
Vol 23 (4) ◽  
pp. 1009-1014 ◽  
Author(s):  
Jian Wang ◽  
Richard G. Hoagland ◽  
Amit Misra
Keyword(s):  
Phase Transition ◽  
Physical Vapor Deposition ◽  
Dislocation Nucleation ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Layered Composites ◽  
Partial Dislocations ◽  
Deposition Parameters ◽  
Face Centered ◽  
Dynamics Simulations

Using classical molecular dynamics simulations, we have investigated the growth of {111} Cu on Nb {110} surface. Our results reveal that the deposited Cu layer initially grows as body-centered cubic (bcc) and Vernier misfits are observed in the interface of bcc Cu and bcc Nb. As it continues to grow, the bcc Cu {110} transforms into face-centered cubic (fcc) Cu {111}. The phase transition starts after the bcc Cu layer has accumulated about 3 monolayers and is finished depending on deposition parameters. Nuclei of fcc Cu {111} form in the top surface of Cu and grow in plane and toward the interface. Partial dislocations in the fcc Cu layer nucleate during the late stage of the transition, and the stacking faults grow as the Cu layer thickens.

A New Phase of the Na+ Ion Conductor Na3PS4

2019 ◽  
Author(s):  
Theodosios Famprikis ◽  
James Dawson ◽  
François Fauth ◽  
Emmanuelle Suard ◽  
Benoit Fleutot ◽  
...  
Keyword(s):  
Solid Electrolytes ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Ion Conductor ◽  
Solid State Batteries ◽  
Density Analysis ◽  
Two Phases ◽  
Dynamics Simulations

<div> <p>Solid electrolytes are crucial for next‑generation solid‑state batteries and Na<sub>3</sub>PS<sub>4</sub> is one of the most promising Na<sup>+</sup> conductors for such applications. At present, two phases of Na<sub>3</sub>PS<sub>4</sub> have been identified and it had been thought to melt above 500 °C. In contrast, we show that it remains solid above this temperature and transforms into a third polymorph, γ, exhibiting superionic behavior. We propose an orthorhombic crystal structure for γ‑Na<sub>3</sub>PS<sub>4</sub> based on scattering density analysis of diffraction data and density functional theory calculations. We show that the Na<sup>+</sup> superionic behavior is associated with rotational motion of the thiophosphate polyanions pointing to a rotor phase, based on <i>ab initio</i> molecular dynamics simulations and supported by high‑temperature synchrotron and neutron diffraction, thermal analysis and impedance spectroscopy. These findings are of importance for the development of new polyanion‑based solid electrolytes.</p> </div>

scholarly journals The Impact of Vibrational Entropy on the Segregation of Cu to Antiphase Boundaries in Fe3Al

2021 ◽  
Vol 7 (8) ◽  
pp. 108
Author(s):  
Martin Friák ◽  
Miroslav Černý ◽  
Mojmír Šob
Keyword(s):  
Magnetic Moments ◽  
Energy Difference ◽  
Extended Defects ◽  
Vibrational Entropy ◽  
Phonon Modes ◽  
Antiphase Boundaries ◽  
Related Energy ◽  
Quantum Mechanical Study ◽  
Nonlinear Trends ◽  
The Impact

We performed a quantum mechanical study of segregation of Cu atoms toward antiphase boundaries (APBs) in Fe3Al. The computed concentration of Cu atoms was 3.125 at %. The APBs have been characterized by a shift of the lattice along the ⟨001⟩ crystallographic direction. The APB energy turns out to be lower for Cu atoms located directly at the APB interfaces and we found that it is equal to 84 mJ/m2. Both Cu atoms (as point defects) and APBs (as extended defects) have their specific impact on local magnetic moments of Fe atoms (mostly reduction of the magnitude). Their combined impact was found to be not just a simple sum of the effects of each of the defect types. The Cu atoms are predicted to segregate toward the studied APBs, but the related energy gain is very small and amounts to only 4 meV per Cu atom. We have also performed phonon calculations and found all studied states with different atomic configurations mechanically stable without any soft phonon modes. The band gap in phonon frequencies of Fe3Al is barely affected by Cu substituents but reduced by APBs. The phonon contributions to segregation-related energy changes are significant, ranging from a decrease by 16% at T = 0 K to an increase by 17% at T = 400 K (changes with respect to the segregation-related energy difference between static lattices). Importantly, we have also examined the differences in the phonon entropy and phonon energy induced by the Cu segregation and showed their strongly nonlinear trends.

Computational studies of ice defects

2003 ◽  
Vol 81 (1-2) ◽  
pp. 325-332 ◽  
Author(s):  
P LM Plummer
Keyword(s):  
Defect Formation ◽  
Structural Evolution ◽  
Energy Difference ◽  
Electronic Energy ◽  
Energy Structure ◽  
Defect Site ◽  
And Migration ◽  
Dynamics Simulations ◽  
Small Clusters ◽  
Structure Calculations

Continuing our investigations of the energetics associated with defect formation and migration, both ab initio energy-structure calculations and molecular dynamics simulations are carried out on small clusters of water molecules containing one or more defects in hydrogen bonding. Previous studies in this series have identified structures containing defects that are stable at 0 K or that are transition states between such structures. However, results from this laboratory and elsewhere have shown that the energy required for the production or migration of a defect is more complex than merely the energy difference between the static structures. Cooperative motion of neighbors to the defect site can either increase or decrease the energy involved to produce or annihilate the defect. Thus, experimental measurements associated with the energy of defects in ice can differ substantially from those calculated using static models. By increasing the complexity of the model, the studies described in this report attempt to more realistically simulate a defect-containing ice system. The types of defects studied include ion and ion-pair defects. The initial structures are energetically stable — minima on the electronic energy surface — and contain one or more kinds of defects. Since the means and amount of energy injection can alter the migration path, the energy is introduced into the system in a variety of ways. The structural evolution of the ice system is then monitored as a function of time. PACS Nos.: 82.20Wt, 82.20Kh, 82.30Rs

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