Collective jumps in a soft-sphere glass

Oligschleger, C.; Schober, H. R.

doi:10.1103/physrevb.59.811

Cited by 137 publications

(148 citation statements)

References 67 publications

Supporting

Mentioning

131

Contrasting

Unclassified

Order By: Relevance

“…18 At higher temperatures, there is an increase in both the atomic displacements and the number of atoms participating in the jumps. 21 It is pertinent to note that, although crystallisation is universally known to be a first-order thermodynamic transformation, 22,23 glass transition has been prevailingly considered as a largely dynamical phenomenon 24 and soft phonons are known to be related to the dynamics of amorphous alloys. 18,25 Although the energy landscape curvature and mean-squared atomic displacements (MSD) are two different quantities, they are inter-connected often in complicated relations.…”

Section: Resultsmentioning

confidence: 99%

Softening of phonon spectra in metallic glasses

et al. 2016

View full text Add to dashboard Cite

The vibrational spectra of a series of MgZnCa amorphous alloys were computed using density functional theory and implementing the small displacement method. The atomic structures of the alloys were obtained by ab initio molecular dynamics simulations. The vibrational thermodynamic properties were calculated as a function of temperature and, in particular, the specific heat at low temperature was approximated by temperature cubed based on the Debye model. We computed the contribution of Mg vibrations to the specific heat and investigated the softening of Mg phonon spectra, where the maximum allowed vibrational frequency is lowered and highly collective diffusion processes are promoted. The statistical correlation between the reported critical casting thickness of the alloys and softening of Mg phonons was obtained. Similar calculations were performed for two distinctively different amorphous ZrTiCuAl alloys with large and small reported critical casting thickness, respectively. The findings were consistent with those of the MgZnCa alloys. INTRODUCTIONThere has been increasing attention devoted to the effect of vibrational thermodynamics on the formation of different alloy phases and their associated phase transformations due to the improved accessibility of instruments capable of measuring and calculating the phonon frequencies. 1 Various thermodynamic properties such as specific heat and vibrational entropy can be derived through the vibrational density of states (VDOSs). The VDOS obtained by molecular dynamics (MD) simulations has provided useful insight into how phonon spectra are affected by both the size and surface properties of silicon nanoparticles; this is of major significance in the design of nanodevices with better heat transport properties. It was found that, as the Si particles become smaller, the density of vibrational states increases at low frequencies, and modes are transferred from the high-frequency end to the intermediate range and transverse optical modes peak are shifted to higher frequencies. 2 In metallic glasses, vibrational characteristics have also been used for explaining mechanical properties. For example, recent MD simulations of a Cu 64 Zr 36 metallic glass showed that the strongest participation in the modes with lowest vibrational frequency and, hence, weakest spring constants (i.e., soft modes) originate predominantly from meagrely populated polyhedra. These soft spots provide fertile sites for accommodating shear transformations. 3 The softening of long wavelength acoustic phonons in PdSiCu, ZrTiCuNiBe, CeAlNiCu and ZrNbCuNiBe amorphous alloys relative to their crystalline phases have been observed experimentally using ultrasound measurements. [4][5][6] Such observations are consistent with the low-temperature measurements of their specific heat, whereby an increase in temperature causes a steeper increase in specific heat in the amorphous alloys compared with their crystalline counterparts.Specific heat is believed to be a fundamental property of materials and, in particular,...

show abstract

Section: Resultsmentioning

confidence: 99%

Softening of phonon spectra in metallic glasses

et al. 2016

View full text Add to dashboard Cite

show abstract

“…Comparing Figs. 5a and 6 one sees the close correlation between quasi-localized vibrations and atomic jumps expressed which we established earlier by correlating vibrational eigenvectors an jump vectors [44]. …”

Section: Relaxationsmentioning

confidence: 94%

“…All observed relaxations were collective jumps localized to 10 and more atoms forming twisted chain-like structures with some side branching [44]. This collectivity is again reflected in the relaxational structure factor, defined in analogy with the vibrational (Eq.…”

Section: Relaxationsmentioning

confidence: 96%

“…They are again collective motions of chains of atoms [44,49]. At low temperatures any given atom moves in such a jump only a fraction of the nearest neighbour distance.…”

Section: Relaxationsmentioning

confidence: 99%

“…The calculations were done using the samples prepared earlier for investigations of vibrations [34] and relaxations [44]. These had been prepared by the following procedure.…”

Section: Computational Detailsmentioning

confidence: 99%

See 2 more Smart Citations

Vibrations and relaxations in a soft sphere glass: boson peak and structure factors

Schober

2004

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

The dynamics of a soft sphere model glass, studied by molecular dynamics, is investigated.The vibrational density of states divided by ω 2 shows a pronounced boson peak. Its shape is in agreement with the universal form derived for soft oscillators interacting with sound waves. The excess vibrations forming the boson peak have mainly transverse character. From the dynamic structure factor in the Brillouin regime pseudo dispersion curves are calculated. Whereas the longitudinal phonons are well defined up to the pseudo zone boundary the transverse ones rapidly get over-damped and go through the Ioffe-Regel limit near the boson peak frequency. In the high q regime constant-ω scans of the dynamic structure factor for frequencies around the boson peak are clearly distinct from those for zone boundary frequencies. Above the Brillouin regime, the scans for the low frequency modes follow closely the static structure factor. This still holds after a deconvolution of the exact harmonic eigenmodes into local and extended modes. Also the structure factor for local relaxations at finite temperatures resembles the static one. This semblance between the structure factors mirrors the collective motion of chain like structures in both low frequency vibrations and atomic hopping processes, observed in the earlier investigations.

show abstract

Vacancies and atomic processes in intermetallics – From crystals to quasicrystals and bulk metallic glasses

Schaefer¹,

Baier²,

Müller³

et al. 2011

Physica Status Solidi (b)

View full text Add to dashboard Cite

A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1 2 -Ni 3 Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe 61 Al 39 and in MoSi 2 . In the icosahedral quasicrystal Al 70 Pd 21 Mn 9 the thermal vacancy concentration is low, whereas in the BMG Zr 57 Cu 15.4 Ni 12.6 Nb 3 Al 10 thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Fähnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics.

show abstract

Collective jumps in a soft-sphere glass

Cited by 137 publications

References 67 publications

Softening of phonon spectra in metallic glasses

Softening of phonon spectra in metallic glasses

Vibrations and relaxations in a soft sphere glass: boson peak and structure factors

Vacancies and atomic processes in intermetallics – From crystals to quasicrystals and bulk metallic glasses

Contact Info

Product

Resources

About