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K F Kelton - One of the best experts on this subject based on the ideXlab platform.

  • maximum supercooling studies in ti39 5zr39 5ni21 ti40zr30ni30 and zr80pt20 liquids connecting liquid structure and the nucleation barrier
    Journal of Chemical Physics, 2019
    Co-Authors: M E Sellers, D C Van Hoesen, A K Gangopadhyay, K F Kelton
    Abstract:

    Almost three quarters of a century ago, Charles Frank proposed that the deep supercooling observed in metallic liquids is due to Icosahedral short-range order (ISRO), which is incompatible with the long-range order of crystal phases. Some evidence in support of this hypothesis had been published previously. However, those studies were based on a small population of maximum supercooling measurements before the onset of crystallization. Here, the results of a systematic statistical study of several hundred maximum supercooling measurements on Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids are presented. Previous X-Ray and neutron scattering studies have shown that the structures of these liquid alloys contain significant amounts of ISRO. The results presented here show a small work of critical cluster formation (W* = 31–40 kBT) from the analysis of the supercooling data for the Ti39.5Zr39.5Ni21 liquid, which crystallizes to a metastable Icosahedral Quasicrystal. A much larger value (W* = 54–79 kBT and W* = 60–99 kBT) was obtained for the Ti40Zr30Ni30 and Zr80Pt20 liquids, respectively, which do not crystallize to an Icosahedral Quasicrystal. Taken together, these results significantly strengthen the validity of Frank’s hypothesis.Almost three quarters of a century ago, Charles Frank proposed that the deep supercooling observed in metallic liquids is due to Icosahedral short-range order (ISRO), which is incompatible with the long-range order of crystal phases. Some evidence in support of this hypothesis had been published previously. However, those studies were based on a small population of maximum supercooling measurements before the onset of crystallization. Here, the results of a systematic statistical study of several hundred maximum supercooling measurements on Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids are presented. Previous X-Ray and neutron scattering studies have shown that the structures of these liquid alloys contain significant amounts of ISRO. The results presented here show a small work of critical cluster formation (W* = 31–40 kBT) from the analysis of the supercooling data for the Ti39.5Zr39.5Ni21 liquid, which crystallizes to a metastable Icosahedral Quasicrystal. A much larger value (W* = 54–79 kBT and...

  • effect of microalloying on the formation and stability of the ti zr ni Icosahedral Quasicrystal
    Journal of Alloys and Compounds, 2012
    Co-Authors: Geun Woo Lee, A K Gangopadhyay, K F Kelton
    Abstract:

    Abstract The influence of small additions of Cu, Ag, Au, Pt, Pb, and Si on the formation and stabilization of Ti–Zr–Ni Icosahedral Quasicrystal (i-phase) are discussed. Among these elements, only the addition of Ag improved the stability and formability of the i-phase, significantly. A small amount of supercooling and the nucleation and growth of only the i-phase from the liquid during levitation melting experiments signal the presence of well developed extended Icosahedral short range order (ISRO) in the liquid. These results are explained in terms of a better atomic size ratio of Ag to Zr to form ISRO.

  • phase diagram studies of ti zr ni alloys containing less than 40 at ni and estimated critical cooling rate for Icosahedral Quasicrystal formation from the liquid
    Acta Materialia, 2011
    Co-Authors: Geun Woo Lee, Anup K. Gangopadhyay, K F Kelton
    Abstract:

    Abstract A detailed phase diagram study of Ti–Zr–Ni alloys has been conducted using conventional X-ray scattering, microstructural and thermal annealing, and levitation techniques, to improve on the existing phase diagram. Various phases, such as simple crystalline, approximant, Icosahedral Quasicrystalline, and complex polytetrahedral phases, have been identified. A eutectic composition has been found near 21 at.% Ni for nearly equal Ti and Zr concentrations. From containerless processing studies, using electrostatic levitation, the phase boundary of the Icosahedral Quasicrystal (i-phase) is placed between 29 and 45 at.% Ti with 21 at.% Ni. A first-time estimate of the critical cooling rate for the formation of the i-phase directly from the liquid in alloys with 21 at.% Ni is less than 100 °C s−1, which is much smaller than for most of the known metastable Quasicrystals.

  • x ray and electrostatic levitation undercooling studies in ti zr ni Quasicrystal forming alloys
    Journal of Non-crystalline Solids, 2002
    Co-Authors: K F Kelton, A K Gangopadhyay, Geun Woo Lee, L Hannet, Robert W Hyers, Shankar Krishnan, M B Robinson, J R Rogers, T J Rathz
    Abstract:

    The first undercooling measurements on electrostatic-levitated droplets of TiZrNi alloys that form the Icosahedral Quasicrystal phase are presented. The reduced undercooling for crystallization decreases with an increasing polytetrahedral order of the primary solidifying phase, suggesting the development of Icosahedral short-range order in the undercooled liquid. X-ray diffraction measurements made at the advanced photon source on liquid droplets of these alloys, aerodynamically levitated and heated to near their liquidus temperature, however, show only weak evidence for increased Icosahedral order. This suggests that significant ordering occurs below the melting temperature.

  • Icosahedral Quasicrystal formation in ti zr based alloys and a new classification technique
    Philosophical Magazine, 1998
    Co-Authors: W J Kim, P C Gibbons, K F Kelton
    Abstract:

    Until recently, Icosahedral phase (i-phase) formation was studied primarily in Al-transition metal alloys. The Al-based i-phases generally fall into one of two classes: those believed to be based on the Pauling triacontahedron, fundamental to the Bergman 1/1 phase, and those based on the double-shell Mackay icosahedra found in the 1/1α-(Al-Mn-Si) phase. Notable Bergman-type Quasicrystals include i-(Al Li-Cu) and i-(Al-Mg-Zn); i-(Al-Mn-Si) forms the best known Mackay-type i-phase. The large number of Ti-based i-phases now known, and the differences in their diffraction features raise the question of their fundamental structural units. To address this partially, results of X-ray and electron microscopy studies of Ti-Zr-Ni alloys, where Ni is replaced by Fe and Co, are reported. The character of the i-phases varies smoothly from the Ti-Zr-Ni Quasicrystals, which probably are Bergman-type i-phases, to the Ti-Zr-Fe Quasicrystals, which probably are Mackay types. A new classification method for Icosahedral Quasicrystals based on the ratio of the quasilattice constant a q to the average atomic separation , computed from the measured density, is introduced and applied to both Al- and Ti-based Quasicrystals. On the basis of this scheme, most Ti-based i-phases, including the Ti-3d transition metal-Si-O phases and Ti Zr Fe, form a third group, different from the Al-based Mackay and Bergman groups. Ti-Zr-Ni and Ti-Zr-Co Quasicrystals fall into the same class as the Bergman-type Al-based i-phases.

A P Tsai - One of the best experts on this subject based on the ideXlab platform.

Tsutomu Ishimasa - One of the best experts on this subject based on the ideXlab platform.

  • Icosahedral Quasicrystal 1 1 and 2 1 approximants in zn based ternary alloys containing au and yb tb
    Philosophical Magazine Letters, 2019
    Co-Authors: Tsutomu Ishimasa
    Abstract:

    In a narrow composition range centred at Zn74.5Au10.5Yb15.0, Tsai-type Icosahedral Quasicrystal is formed in alloys quenched from 880°C. This Quasicrystal belongs to the primitive type with the 6-d...

  • Icosahedral Quasicrystal 1 1 and 2 1 approximants in zn based ternary alloys containing au and yb tb
    arXiv: Materials Science, 2019
    Co-Authors: Tsutomu Ishimasa
    Abstract:

    In a narrow composition range centered at Zn74.5Au10.5Yb15.0, Tsai-type Icosahedral Quasicrystal is formed in alloys quenched from 880 C. This Quasicrystal belongs to the primitive type with the 6-dimensional lattice parameter a6D=7.378 A. The Quasicrystal was not formed in the slowly cooled specimen, and was considered a metastable phase. The stable phase is a 2/1 approximant of the lattice parameter a2/1=23.271 A. This approximant forms exclusively in Zn76.0Au9.0Yb15.0 alloy annealed at 530 C. In addition, Zn70.5Au15.5Tb14.0 alloy annealed at 505 C forms a Tsai-type 1/1 approximant (a1/1=14.343 A). These new Zn-based phases observed in this study correspond to the Quasicrystal-related phases in binary Cd-lanthanoid systems, and show the possibility of isostructural substitution of Cd by Zn/Au.

  • pressure driven quantum criticality and t h scaling in the Icosahedral au al yb approximant
    Journal of the Physical Society of Japan, 2016
    Co-Authors: Shuya Matsukawa, Tsutomu Ishimasa, Kazuhiko Deguchi, Keiichiro Imura, N Sato
    Abstract:

    We report on ac magnetic susceptibility measurements under pressure of the Au–Al–Yb alloy, a crystalline approximant to the Icosahedral Quasicrystal that shows unconventional quantum criticality. In describing the susceptibility as χ(T)−1 − χ(0)−1 ∝ Tγ, we find that χ(0)−1 decreases with increasing pressure and vanishes to zero at the critical pressure \(P_{\text{c}} \simeq 2\) GPa, with γ (\( \simeq 0.5\)) unchanged. We suggest that this quantum criticality emerges owing to critical valence fluctuations. Above Pc, the approximant undergoes a magnetic transition at \(T \simeq 100\) mK. These results are contrasted with the fact that, in the Quasicrystal, the quantum criticality is robust against the application of pressure. The applicability of the so-called T/H scaling to the approximant is also discussed.

  • pressure driven quantum criticality and t h scaling in the Icosahedral au al yb approximant
    arXiv: Strongly Correlated Electrons, 2016
    Co-Authors: Shuya Matsukawa, Tsutomu Ishimasa, Kazuhiko Deguchi, Keiichiro Imura, N Sato
    Abstract:

    We report on ac magnetic susceptibility measurements under pressure of the Au-Al-Yb alloy, a crystalline approximant to the Icosahedral Quasicrystal that shows unconventional quantum criticality. In describing the susceptibility as $\chi(T)^{-1} - \chi(0)^{-1} \propto T^{\gamma}$, we find that $\chi(0)^{-1}$ decreases with increasing pressure and vanishes to zero at the critical pressure $P_{\rm c} \simeq 2$ GPa, with $\gamma~ (\simeq 0.5)$ unchanged. We suggest that this quantum criticality emerges owing to critical valence fluctuations. Above $P_{\rm c}$, the approximant undergoes a magnetic transition at $T \simeq 100$ mK. These results are contrasted with the fact that, in the Quasicrystal, the quantum criticality is robust against the application of pressure. The applicability of the so-called $T/H$ scaling to the approximant is also discussed.

  • Icosahedral Quasicrystal and 1 1 cubic approximant in au al yb alloys
    Philosophical Magazine, 2011
    Co-Authors: Tsutomu Ishimasa, Yukinori Tanaka, Shiro Kashimoto
    Abstract:

    A P-type Icosahedral Quasicrystal is formed in an Au–Al–Yb alloy with a six-dimensional lattice parameter a 6D = 7.448 A. The composition of the Quasicrystal was analyzed to be Au51Al34Yb15. The Quasicrystal is formed in as-cast alloys and is regarded as metastable with decomposition to other crystalline phases during annealing at 700°C. Among Tsai-type Quasicrystals, this Quasicrystal is situated just between the Zn–Sc group with a smaller a 6D and the larger Cd–Yb group. The intermediate valence of Yb recently observed in this Quasicrystal may be due to this unique situation, namely a smaller major component in Au-Al-Yb than in Cd–Yb. The predominant phase in the annealed specimen is a 1/1 cubic approximant with lattice parameter a = 14.500 A belonging to the space group Im . This phase is stable at the composition Au51Al35Yb14 at 700°C. Rietveld structural analysis indicated that the crystal structure is a periodic arrangement of Tsai-type clusters with four Au–Al atoms at their centers. Chemical order...

Kaoru Shibata - One of the best experts on this subject based on the ideXlab platform.

  • Lattice dynamics of the Zn–Mg–Sc Icosahedral Quasicrystal and its Zn–Sc periodic 1/1 approximant
    Nature Materials, 2007
    Co-Authors: M. De Boissieu, S. Francoual, Tsutomu Ishimasa, Marek Mihalkovič, Kaoru Shibata, Alfred Q. R. Baron, Yvan Sidis, Thomas Lograsso, Louis-pierre Regnault, Franz Gähler
    Abstract:

    Quasicrystals are long-range-ordered materials that lack translational invariance, so the study of their physical properties remains a challenging problem. Here, we have carried out inelastic-X-ray- and neutron-scattering experiments on single-grain samples of the Zn–Mg–Sc Icosahedral Quasicrystal and of the Zn–Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the Quasicrystal. This can be qualitatively explained using the concept of a pseudo-Brillouin-zone in the Quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results. This paves the way for a detailed understanding of the physics of Quasicrystals.

  • antiferromagnetic spin correlations in the zn mg ho Icosahedral Quasicrystal
    Physical Review B, 2000
    Co-Authors: Taku J Sato, Kaoru Shibata, Hiroyuki Takakura, A P Tsai, Kenji Ohoyama, K H Andersen
    Abstract:

    Magnetic diffuse scattering in the Zn-Mg-Ho Icosahedral Quasicrystal has been studied by neutron scattering over a wide $\mathit{Q}$ range using a single-Quasicrystalline sample. It was found that the diffuse scattering obeys the Icosahedral symmetry, and appears as satellite peaks of the intense nuclear Bragg reflections. The diffuse-scattering patterns were successfully accounted for by assuming short-range spin correlations in a six-dimensional hypercubic crystal with a magnetic modulation vector $\mathit{q}=(\frac{3}{4},0,0,\frac{1}{2},\frac{3}{4},\frac{1}{2}{)}_{{\mathit{a}}^{*}}.$ A possible origin for the six-dimensional spin correlations is discussed.

  • anisotropic spin correlations in the zn mg ho Icosahedral Quasicrystal
    Physical Review Letters, 1998
    Co-Authors: Taku J Sato, Hiroyuki Takakura, A P Tsai, Kaoru Shibata
    Abstract:

    Neutron scattering experiments have been performed on the Zn-Mg-Ho Icosahedral Quasicrystal using powder and single-crystalline samples. In contrast to a previous Letter [Charrier et al., Phys. Rev. Lett. 78, 4637 (1997)], the magnetic long-range order could not be detected in the Icosahedral Quasicrystal. It instead exhibits highly anisotropic diffuse scattering, which appears as satellite ridges of intense nuclear Bragg reflections, running parallel to the fivefold axis. The result suggests that quasi-five-dimensional spin correlations develop on a six-dimensional hypercubic lattice.

Geun Woo Lee - One of the best experts on this subject based on the ideXlab platform.

  • effect of microalloying on the formation and stability of the ti zr ni Icosahedral Quasicrystal
    Journal of Alloys and Compounds, 2012
    Co-Authors: Geun Woo Lee, A K Gangopadhyay, K F Kelton
    Abstract:

    Abstract The influence of small additions of Cu, Ag, Au, Pt, Pb, and Si on the formation and stabilization of Ti–Zr–Ni Icosahedral Quasicrystal (i-phase) are discussed. Among these elements, only the addition of Ag improved the stability and formability of the i-phase, significantly. A small amount of supercooling and the nucleation and growth of only the i-phase from the liquid during levitation melting experiments signal the presence of well developed extended Icosahedral short range order (ISRO) in the liquid. These results are explained in terms of a better atomic size ratio of Ag to Zr to form ISRO.

  • phase diagram studies of ti zr ni alloys containing less than 40 at ni and estimated critical cooling rate for Icosahedral Quasicrystal formation from the liquid
    Acta Materialia, 2011
    Co-Authors: Geun Woo Lee, Anup K. Gangopadhyay, K F Kelton
    Abstract:

    Abstract A detailed phase diagram study of Ti–Zr–Ni alloys has been conducted using conventional X-ray scattering, microstructural and thermal annealing, and levitation techniques, to improve on the existing phase diagram. Various phases, such as simple crystalline, approximant, Icosahedral Quasicrystalline, and complex polytetrahedral phases, have been identified. A eutectic composition has been found near 21 at.% Ni for nearly equal Ti and Zr concentrations. From containerless processing studies, using electrostatic levitation, the phase boundary of the Icosahedral Quasicrystal (i-phase) is placed between 29 and 45 at.% Ti with 21 at.% Ni. A first-time estimate of the critical cooling rate for the formation of the i-phase directly from the liquid in alloys with 21 at.% Ni is less than 100 °C s−1, which is much smaller than for most of the known metastable Quasicrystals.

  • x ray and electrostatic levitation undercooling studies in ti zr ni Quasicrystal forming alloys
    Journal of Non-crystalline Solids, 2002
    Co-Authors: K F Kelton, A K Gangopadhyay, Geun Woo Lee, L Hannet, Robert W Hyers, Shankar Krishnan, M B Robinson, J R Rogers, T J Rathz
    Abstract:

    The first undercooling measurements on electrostatic-levitated droplets of TiZrNi alloys that form the Icosahedral Quasicrystal phase are presented. The reduced undercooling for crystallization decreases with an increasing polytetrahedral order of the primary solidifying phase, suggesting the development of Icosahedral short-range order in the undercooled liquid. X-ray diffraction measurements made at the advanced photon source on liquid droplets of these alloys, aerodynamically levitated and heated to near their liquidus temperature, however, show only weak evidence for increased Icosahedral order. This suggests that significant ordering occurs below the melting temperature.