Keywords :
Theoretical or Mathematical/ ab initio calculations; antimony alloys; entropy; germanium alloys; liquid alloys; molecular dynamics method; neutron diffraction; phase change materials; tellurium alloys; thermal expansion; vibrational modes/ negative thermal expansion; tellurium based liquid alloys; atomic vibrational properties; neutron inelastic scattering; structural evolution; vibrational entropy; Peierls distortion; vibrational density of states; first principles molecular dynamics simulations; phase-change materials; temperature dependance; GeTe 6; GeTe 12; GeSb 2Te 4; Ge 2Sb 2Te 5/ A6570 Thermal expansion and thermomechanical effects A6350 Vibrational states in disordered systems A6550 Thermodynamic properties and entropy A7115A Ab initio calculations (condensed matter electronic structure) A7115Q Molecular dynamics calculations and other numerical simulations (condensed matter electronic structure) A6125M Structure of liquid metals and liquid alloys/ GeTe6/bin Te6/bin Ge/bin Te/bin; GeTe12/bin Te12/bin Ge/bin Te/bin; GeSb2Te4/ss Te4/ss Sb2/ss Ge/ss Sb/ss Te/ss; Ge2Sb2Te5/ss Te5/ss Ge2/ss Sb2/ss Ge/ss Sb/ss Te/ss
Abstract :
[en] Negative thermal expansion (NTE) in tellurium based liquid alloys (GeTe 6 and GeTe 12) is analyzed through the atomic vibrational properties. Using neutron inelastic scattering, we show that the structural evolution resulting in the NTE is due to a gain of vibrational entropy that cancels out the Peierls distortion. In the NTE temperature range, these competing effects give rise to noticeable changes in the vibrational density of states spectra. Additional first principles molecular dynamics simulations emphasize the role of the temperature dependance of the Ge atomic environment in this mechanism. For comparison, we extended our study to Ge 2Sb 2Te 5 and Ge 1Sb 2Te 4 phase-change materials.
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