A Mössbauer spectrometry study of nanophase CrFe synthesized by mechanical alloying: A measurement of grain boundary width

Kuwano, Hisashi; Ouyang, Hao; Fultz, B.

doi:10.1016/0965-9773(92)90067-8

Cited by 41 publications

(22 citation statements)

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“…In the meV energy range of the Pharos and LRMECS instruments, an enhancement by a factor of 1:30 0:05 is observed, consistent with previous mea- surements on Fe with 12 nm nanocrystals [8]. Such an enhancement is also present in the Ni 3 Fe data, but a spectral component with broad tails, centered around " 0, is observed in the spectrum of the nanocrystalline Ni 3 Fe at 293 K in the HFBS data. This component likely originates with quasielastic scattering from a trace amount of hydrogen within the nanocrystalline sample.…”

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confidence: 76%

“…The spectra measured at 50 K, where hydrogen motions are expected to be frozen out, show less of this possible quasielastic scattering and have a flat energy spectrum beyond 10 eV. Avoiding this quasielastic scattering, we find that the enhancement of modes in the nanocrystals of Ni 3 Fe is similar at 293 and 50 K for energies above approximately 10 eV, consistent with phonon scattering. For Ni 3 Fe the enhancement in the nanocrystalline phonon DOS is a factor of 1:40 0:1 in the eV energy range and a factor of 1:9 0:15 in the meV energy range.…”

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confidence: 61%

“…Avoiding this quasielastic scattering, we find that the enhancement of modes in the nanocrystals of Ni 3 Fe is similar at 293 and 50 K for energies above approximately 10 eV, consistent with phonon scattering. For Ni 3 Fe the enhancement in the nanocrystalline phonon DOS is a factor of 1:40 0:1 in the eV energy range and a factor of 1:9 0:15 in the meV energy range.…”

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confidence: 51%

“…DOI: 10.1103/PhysRevLett.93.205501 PACS numbers: 63.22.+m, 61.46.+w, 81.07.-b The vibrational spectra of nanocrystalline materials differ from those of materials composed of larger crystals. Earlier measurements of Debye-Waller factors and Lamb-Mössbauer factors showed large mean-squared atomic displacements in nanocrystalline materials [1][2][3][4]. More recently, neutron and x-ray inelastic scattering measurements revealed that nanocrystalline materials have an increased number of vibrational modes at the highest and lowest energies of their measured spectra, compared to materials with crystals of conventional sizes [5][6][7][8][9][10][11][12].…”

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confidence: 99%

“…1(c) and 2(c) show that the van Hove singularities for the longitudinal modes are at the same energies in the nanocrystalline and control samples (at 36 and 33 meV for Fe and Ni 3 Fe, respectively). Similarly, the van Hove singularities for the transverse modes, although broadened in energy, are not shifted in energy in the nanocrystalline materials (a systematic series of spectra for Ni 3 Fe is shown in [10]). It appears that the short-range interatomic forces for atoms within the nanocrystals are not altered significantly by the nanocrystalline microstructure.…”

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Vibrations of Micro-eV Energies in Nanocrystalline Microstructures

et al. 2004

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The phonon density of states of nanocrystalline bcc Fe and nanocrystalline fcc Ni 3 Fe were measured by inelastic neutron scattering in two different ranges of energy. As has been reported previously, the nanocrystalline materials showed enhancements in their phonon density of states at energies from 2 to 15 meV, compared to control samples composed of large crystals. The present measurements were extended to energies in the micro-eV range, and showed significant, but smaller, enhancements in the number of modes in the energy range from 5 to 18 eV. These modes of micro-eV energies provide a long-wavelength limit that bounds the fraction of modes at milli-eV energies originating with the cooperative dynamics of the nanocrystalline microstructure. DOI: 10.1103/PhysRevLett.93.205501 PACS numbers: 63.22.+m, 61.46.+w, 81.07.-b The vibrational spectra of nanocrystalline materials differ from those of materials composed of larger crystals. Earlier measurements of Debye-Waller factors and Lamb-Mössbauer factors showed large mean-squared atomic displacements in nanocrystalline materials [1][2][3][4]. More recently, neutron and x-ray inelastic scattering measurements revealed that nanocrystalline materials have an increased number of vibrational modes at the highest and lowest energies of their measured spectra, compared to materials with crystals of conventional sizes [5][6][7][8][9][10][11][12]. Enhanced intensity above the high-energy cutoff of the bulk material has been attributed to phonon lifetime broadening caused by phonon interactions with grain boundaries [9][10][11] and recent measurements on iron have isolated a contribution from surface oxides [12]. The increased number of phonon modes at low energies [5][6][7][8][9][10][11] is less well understood. The phonon density of states (DOS) at low energies is up to a factor of 5 times larger than the DOS of control samples of material composed of larger crystals [10]. The number of these low-energy modes was found to increase with the inverse of the crystallite size, implying a scaling with the number of grain boundaries. Surface vibrational modes could be responsible for such behavior because grain boundaries have elastic constants differing from the crystal interiors. There are some experimental and computational reports that the low-energy phonon DOS in nanocrystalline materials scales linearly with energy, indicative of twodimensional vibrations [13,14]. Other theoretical models include the idea of a nonintegral spatial dimension of the low-energy modes [15][16][17][18].Surface modes on individual, isolated crystallites have a maximum wavelength comparable to the crystallite size, and therefore a lower bound on their energy. For a wave velocity of 2 km=s and a particle of 10 nm dimension, the characteristic energy is 1 meV. Energies of a milli-electron volt have been approximately the lower limit of the inelastic spectra measured to date. Surface modes around nanoparticles should not extend to energies much below 100 eV, however. The present experiment was d...

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confidence: 61%

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confidence: 51%