Dynamics of the Negative Thermal Expansion in Tellurium Based Liquid Alloys

Otjacques, C.; Raty, Jean‐Yves; Coulet, Marie‐Vanessa; Johnson, Mark R.; Schober, H.; Bichara, Christophe; Gaspard, Jean-Pierre

doi:10.1103/physrevlett.103.245901

Cited by 23 publications

(29 citation statements)

References 25 publications

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“…56 In this picture, at low temperature the octahedral local structure is distorted by a Peierlslike mechanism, while at high temperature the symmetry of structure is recovered. The driving force of removing Peierls distortion at high temperature was explained in terms of gain of vibrational entropy by Otjacques et al 57 Indeed, a gain in vibrational entropy consequent on some configurational rearrangement has been associated with an increase in fragility in other cases, where the excess entropy rather than the mere configurational entropy has been invoked as the important quantity on which to focus. 58 D. Fragile-strong transition, water-like phenomena, and their relevance to phase-change memory behaviors This brings us to consideration of the switching alloys themselves to which so much attention has been given.…”

Section: Entropy the Adam-gibbs Prediction Of Viscosity And Fragimentioning

confidence: 99%

Phase change alloy viscosities down to Tg using Adam-Gibbs-equation fittings to excess entropy data: A fragile-to-strong transition

Wei

Lucas

Angell

2015

Journal of Applied Physics

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A method to enhance the data transfer rate of eutectic Sb-Te phase-change recording media A striking anomaly in the viscosity of Te 85 Ge 15 alloys noted by Greer and coworkers from the work of Neumann et al. is reminiscent of the equally striking comparison of liquid tellurium and water anomalies documented long ago by Kanno et al. In view of the power laws that are used to fit the data on water, we analyze the data on Te 85 Ge 15 using the Speedy-Angell power-law form, and find a good account with a singularity T s only 25 K below the eutectic temperature. However, the heat capacity data in this case are not diverging, but instead exhibit a sharp maximum like that observed in fast cooling in the Molinero-Moore model of water. Applying the Adam-Gibbs viscosity equation to these calorimetric data, we find that there must be a fragile-to-strong liquid transition at the heat capacity peak temperature, and then predict the "strong" liquid course of the viscosity down to T g at 406 K (403.6 K at 20 K min À1 in this study). Since crystallization can be avoided by moderately fast cooling in this case, we can check the validity of the extrapolation by making a direct measurement of fragility at T g , using differential scanning calorimetric techniques, and then comparing with the value from the extrapolated viscosity at T g . The agreement is encouraging, and prompts discussion of relations between water and phase change alloy anomalies. V C 2015 AIP Publishing LLC. [http://dx.

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Section: Entropy the Adam-gibbs Prediction Of Viscosity And Fragimentioning

confidence: 99%

Phase change alloy viscosities down to Tg using Adam-Gibbs-equation fittings to excess entropy data: A fragile-to-strong transition

Wei

Lucas

Angell

2015

Journal of Applied Physics

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“…The inelastic neutron scattering measurements presented in section 4, together with the analysis of the vibrational entropy contribution discussed in [23] provide the answer. The low temperature liquid phase is stabilized by the Peierls distortion mechanism leading to the symmetry breaking of the local octahedral environment of each atom.…”

Section: Discussionmentioning

confidence: 90%

“…The softer vibrational modes at higher temperature give rise to a larger vibrational entropy. As shown in [23] this vibrational contribution amounts to about 60% of the total entropy variation calculated by integrating the heat capacity data.…”

Section: Inelastic Scattering Experimentsmentioning

confidence: 99%

A comparative thermodynamic and structural investigation of Ge_xTe_(1−x)and Ge_xSb_yTe_(1−x−y)liquid alloys

Otjacques

Raty

Gaspard

et al. 2011

Journées de la Neutronique

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Abstract. Thermodynamic properties (density and sound velocity) of liquid GeSb 2 Te 4 and Ge 2 Sb 2 Te 5 alloys have been measured and compared with previously published data on Ge 0.075 Te 0.925 and Ge 0.15 Te 0.85 alloys that display a negative thermal expansion (NTE) in the liquid state. This comparison is extended to the analysis of their structural and dynamical properties investigated by neutron scattering measurements performed on the D4 and IN6 spectrometers at the ILL (Grenoble). These experimental results, complemented by First Principles Molecular Dynamics simulations of the liquids, lead us to propose a model for the density anomaly observed in some of these tellurium based systems, when they are not too dense: it corresponds to a structural change between a low temperature liquid, characterized by a low density and an octahedral local order distorted by a Peierls-like distortion mechanism, and a high temperature liquid in which the vibrational entropy gain favors a more symmetric (less distorted) octahedral local order.

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“…12 These evolutions can be understood as resulting from a gain of vibrational entropy that cancels out or at least weakens the Peierls distortion when the temperature increases in the NTE temperature range. 12 At low temperature, the Ge atoms are off-center in their cage of Te atoms and at higher temperatures they rattle around the center of the shrinked cage. In this picture the NTE results from competing effects ͑Peierls symmetry-breaking mechanism and entropic symmetry-restoring mechanism͒.…”

Section: Introductionmentioning

confidence: 99%

“…11 The structural evolution resulting in the NTE is accompanied by noticeable changes in the vibrational density of states spectra ͑redshift of the high-energy modes͒. 12 These evolutions can be understood as resulting from a gain of vibrational entropy that cancels out or at least weakens the Peierls distortion when the temperature increases in the NTE temperature range. 12 At low temperature, the Ge atoms are off-center in their cage of Te atoms and at higher temperatures they rattle around the center of the shrinked cage.…”

Section: Introductionmentioning

confidence: 99%

Structural and vibrational study of the negative thermal expansion in liquidAs2Te3

et al. 2010

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We present an experimental and theoretical study of liquid As 2 Te 3 . This alloy exhibits a negative thermal expansion ͑NTE͒ in a 250 K range above the melting temperature T m = 654 K. We evidence the changes in As 2 Te 3 structure by measuring neutron-diffraction spectra at five temperatures in the NTE range and perform first principles molecular dynamics simulations at the same temperatures and densities to study the local order evolution in the liquid. Our calculated structures show an increase in the coordination numbers and a symmetrization of the first neighbors shell around atoms when the temperature rises. To confirm these results, we performed inelastic neutron scattering to obtain the vibrational density of state ͑VDOS͒ along the NTE. We see a clear change in the VDOS, consisting in a redshift of the highest frequencies with temperature. Finally, electrical conductivity evolution was obtained from the simulated structures, to compare with the semiconductor to metal transition measured experimentally.

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Dynamics of the Negative Thermal Expansion in Tellurium Based Liquid Alloys

Cited by 23 publications

References 25 publications

Phase change alloy viscosities down to Tg using Adam-Gibbs-equation fittings to excess entropy data: A fragile-to-strong transition

Phase change alloy viscosities down to Tg using Adam-Gibbs-equation fittings to excess entropy data: A fragile-to-strong transition

A comparative thermodynamic and structural investigation of Ge_xTe_(1−x)and Ge_xSb_yTe_(1−x−y)liquid alloys

Structural and vibrational study of the negative thermal expansion in liquidAs2Te3

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Dynamics of the Negative Thermal Expansion in Tellurium Based Liquid Alloys

Cited by 23 publications

References 25 publications

Phase change alloy viscosities down to Tg using Adam-Gibbs-equation fittings to excess entropy data: A fragile-to-strong transition

Phase change alloy viscosities down to Tg using Adam-Gibbs-equation fittings to excess entropy data: A fragile-to-strong transition

A comparative thermodynamic and structural investigation of GexTe(1−x)and GexSbyTe(1−x−y)liquid alloys

Structural and vibrational study of the negative thermal expansion in liquidAs2Te3

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A comparative thermodynamic and structural investigation of Ge_xTe_(1−x)and Ge_xSb_yTe_(1−x−y)liquid alloys