References of "johnson, M"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailStructural and vibrational study of the negative thermal expansion in liquid As2Te3
Otjacques, C.; Raty, Jean-Yves ULg; Hippert, F. et al

in Physical Review. B, Condensed Matter and Materials Physics (2010), 82(5), 0542029-05420290542029

We present an experimental and theoretical study of liquid As 2Te 3. This alloy exhibits a negative thermal expansion (NTE) in a 250 K range above the melting temperature T m = 654 K. We evidence the ... [more ▼]

We present an experimental and theoretical study of liquid As 2Te 3. This alloy exhibits a negative thermal expansion (NTE) in a 250 K range above the melting temperature T m = 654 K. We evidence the changes in As 2Te 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 (VDOS) 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. [less ▲]

Detailed reference viewed: 27 (6 ULg)
Full Text
Peer Reviewed
See detailDynamics of the negative thermal expansion in tellurium based liquid alloys
Otjacques, C.; Raty, Jean-Yves ULg; Coulet, M-V et al

in Physical Review Letters (2009), 103(24), 2459014-24590142459014

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 ... [more ▼]

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. [less ▲]

Detailed reference viewed: 29 (1 ULg)
Full Text
Peer Reviewed
See detailTemperature-induced density anomaly in Te-rich liquid Germanium tellurides: p versus sp 3 bonding?
Bichara, C.; Johnson, M.; Raty, Jean-Yves ULg

in Physical Review Letters (2005), 95(26), 2678011-26780142678014

The density anomaly of liquid Ge 0.15Te 0.85 measured between 633 and 733 K is investigated with ab initio molecular dynamics calculations at four temperatures and at the corresponding experimental ... [more ▼]

The density anomaly of liquid Ge 0.15Te 0.85 measured between 633 and 733 K is investigated with ab initio molecular dynamics calculations at four temperatures and at the corresponding experimental densities. For box sizes ranging from 56 to 112 atoms, an 8 k-points sampling of the Brillouin zone is necessary to obtain reliable results. Contrary to other Ge chalcogenides, no sp 3 hybridization of the Ge bonding is observed. As a consequence, the negative thermal expansion of the liquid is not related to a tetrahedral bonding as in the case of water or silica. We show that it results from the symmetry recovery of the local environment of Ge atoms that is distorted at low temperature by a Peierls-like mechanism acting in the liquid state in the same way as in the parent solid phases [less ▲]

Detailed reference viewed: 19 (1 ULg)