Mechanism for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>α</mml:mi><mml:mo>→</mml:mo><mml:mi>ε</mml:mi></mml:mrow></mml:math>phase transition in iron

Dupé, Bertrand; Amadon, Bernard; Pellegrini, Yves-Patrick; Denoual, Christophe

doi:10.1103/physrevb.87.024103

Cited by 38 publications

(23 citation statements)

References 32 publications

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“…In addition to a discontinuity in volume, the reported MEP cusp was rounded due to the use of an approximate symmetry-adapted polynomial to analytically determine the entire potential energy surface. More recently, possible concerted transformations were investigated (including 3 shuffling mechanisms within the RNM at constant shear and fixed 71.5 bohrs 3 /atom volume), finding a TS in the form of a cusp, 27 but missing the observed magneto-volume collapse-disappearance of magnetization with a concomitant 11% drop in volume.…”

Section: Introductionmentioning

confidence: 99%

Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure

Zarkevich

Johnson

2015

The Journal of Chemical Physics

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We extend the solid-state nudged elastic band method to handle a non-conserved order parameter, in particular, magnetization, that couples to volume and leads to many observed effects in magnetic systems. We apply this formalism to the well-studied magneto-volumecollapse during the pressure-induced transformation in iron-from ferromagnetic body-centered cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We find a bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and coherent stress occurs at the transition state, which has a form of a cusp on the potential-energy surface (yet all the atomic and cell degrees of freedom are continuous); the calculated pressure jump of 25 GPa is related to the observed 25 GPa spread in measured coexistence pressures arising from martensitic and coherency stresses in samples. Our results agree with experiments, but necessarily differ from those arising from drag and restricted parametrization methods having improperly constrained or uncontrolled degrees of freedom. We extend the solid-state nudged elastic band method to handle a non-conserved order parameter, in particular, magnetization, that couples to volume and leads to many observed effects in magnetic systems. We apply this formalism to the well-studied magneto-volume collapse during the pressure-induced transformation in iron-from ferromagnetic body-centered cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We find a bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and coherent stress occurs at the transition state, which has a form of a cusp on the potential-energy surface (yet all the atomic and cell degrees of freedom are continuous); the calculated pressure jump of 25 GPa is related to the observed 25 GPa spread in measured coexistence pressures arising from martensitic and coherency stresses in samples. Our results agree with experiments, but necessarily differ from those arising from drag and restricted parametrization methods having improperly constrained or uncontrolled degrees of freedom. C 2015 AIP Publishing LLC. [http://dx

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Section: Introductionmentioning

confidence: 99%

Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure

Zarkevich

Johnson

2015

The Journal of Chemical Physics

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“…The transformation occurs by a non-diffusive martensitic process and can be viewed as a combination of an anisotropic compression in the (100) direction of the bcc phase with a shuffle in the (011) plane [244]. Therefore, the bcc-hcp structural phase transformation can be propagated in iron at a speed as high as the sound velocity, 5 × 10 5 m/s [245,246]. As shown in the next subsection and Section 4, it can be experimentally demonstrated that the timescale for the MBE InAs QD formation process on the GaAs(001) substrate is quite short, which is obviously inconsistent with the kinetic models based on surface relaxation, adatom aggregation, and nanocrystal growth described in the previous subsections of this section.…”

Section: Review Articlementioning

confidence: 99%

Self-assembly of InAs quantum dots on GaAs(001) by molecular beam epitaxy

Jin

2015

Front. Phys.

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Currently, the nature of self-assembly of three-dimensional epitaxial islands or quantum dots (QDs) in a lattice-mismatched heteroepitaxial growth system, such as InAs/GaAs(001) and Ge/Si(001) as fabricated by molecular beam epitaxy (MBE), is still puzzling. The purpose of this article is to discuss how the self-assembly of InAs QDs in MBE InAs/GaAs(001) should be properly understood in atomic scale. First, the conventional kinetic theories that have traditionally been used to interpret QD self-assembly in heteroepitaxial growth with a significant lattice mismatch are reviewed briefly by examining the literature of the past two decades. Second, based on their own experimental data, the authors point out that InAs QD self-assembly can proceed in distinctly different kinetic ways depending on the growth conditions and so cannot be framed within a universal kinetic theory, and, furthermore, that the process may be transient, or the time required for a QD to grow to maturity may be significantly short, which is obviously inconsistent with conventional kinetic theories. Third, the authors point out that, in all of these conventional theories, two well-established experimental observations have been overlooked: i) A large number of “floating” indium atoms are present on the growing surface in MBE InAs/GaAs(001); ii) an elastically strained InAs film on the GaAs(001) substrate should be mechanically unstable. These two well-established experimental facts may be highly relevant and should be taken into account in interpreting InAs QD formation. Finally, the authors speculate that the formation of an InAs QD is more likely to be a collective event involving a large number of both indium and arsenic atoms simultaneously or, alternatively, a morphological/structural transformation in which a single atomic InAs sheet is transformed into a three-dimensional InAs island, accompanied by the rehybridization from the sp 2-bonded to sp 3-bonded atomic configuration of both indium and arsenic elements in the heteroepitaxial growth system.

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“…This figure is analogous to Fig. 4 from [11] and provide an information about transition thresholds along the Burgers+Shuffle pathway. The general conclusion is that …”

Section: Interatomic Potential and Basic Properties Of Hcp And Bcc Ironmentioning

confidence: 99%

“…Next, we calculated energy dependence on the deformation along the Burgers path and compared the obtained results with the results of calculations performed with the VASP code [9,10]. In VASP calculations 8 atom supercell analogous to that from [11] was used. The bccphase was taken as having ferromagnetic structure and hcp-phase as having antiferromagnetic AFM I structure.…”

Section: Interatomic Potential and Basic Properties Of Hcp And Bcc Ironmentioning

confidence: 99%

“…The following potentials were tested in [5]: Mendelev [6], MEAM-p [7], Ackland [5] and Voter [4]. The goal of present work is an investigation into microscopic mechanisms of the bcc-hcp polymorphous transformation in iron, namely, the role of Burgers mechanism accompanied by the shuffle of atomic layers (see [11]) and preexisting dislocations. In particular, the generation of dislocations and the plasticity mechanisms taking place during pure Burgers deformation of α-iron samples and the effect of dislocations on the time of -phase critical embryos generation are investigated.…”

Section: Introductionmentioning

confidence: 99%

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MD modeling of screw dislocation influence upon initiation and mechanism of BCC-HCP polymorphous transition in iron

Dremov

Ionov

Sapozhnikov

et al. 2015

EPJ Web of Conferences

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Abstract. The present work is devoted to classical molecular dynamics investigation into microscopic mechanisms of the bcchcp transition in iron. The interatomic potential of EAM type used in the calculations was tested for the capability to reproduce ab initio data on energy evolution along the bcc-hcp transformation path (Burgers deformation + shuffle) and then used in the large-scale MD simulations. The large-scale simulations included constant volume deformation along the Burgers path to study the origin and nature of the plasticity, hydrostatic volume compression of defect free samples above the bcc to hcp transition threshold to observe the formation of new phase embryos, and the volume compression of samples containing screw dislocations to study the effect of the dislocations on the probability of the new phase critical embryo formation. The volume compression demonstrated high level of metastability. The transition starts at pressure much higher than the equilibrium one. Dislocations strongly affect the probability of the critical embryo formation and significantly reduce the onset pressure of transition. The dislocations affect also the resulting structure of the samples upon the transition. The formation of layered structure is typical for the samples containing the dislocations. The results of the simulations were compared with the in-situ experimental data on the mechanism of the bcc-hcp transition in iron.

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Mechanism for theα→εphase transition in iron

Cited by 38 publications

References 32 publications

Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure

Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure

Self-assembly of InAs quantum dots on GaAs(001) by molecular beam epitaxy

MD modeling of screw dislocation influence upon initiation and mechanism of BCC-HCP polymorphous transition in iron

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