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Atomic and electronic structure of GST phase change materials

Christophe Bichara 1Jean-Yves Raty 2Céline Otjacques Jean Pierre Gaspard 

1. Centre de Recherche en Matière Condensée et Nanosciences (CRMCN-CNRS), Campus de Luminy, case 913, Marseille 13288, France
2. University of Liege (ULg), B5, Liège 4000, Belgium

Abstract

Understanding the structure of phase change (PC) materials in their amorphous and metastable crystalline phase and their working mechanisms is of major importance.

While many groups have focused their attention on the structure of the crystalline or amorphous states, we start from studies of the liquid state of germanium tellurides. Combining experiments on liquids (thermodynamics, neutron scattering, EXAFS) and computer simulations (RMC, first principles Molecular Dynamics) we end up with a model emphasizing the role of electronically driven distortions of the local octahedral order in the peculiar behavior of these liquids (see references).

We will present DFT based molecular dynamics simulations of Ge2Sb2Te5 alloys in crystalline, liquid and amorphous states. The interpretation of these results in the same framework leads to a simple and original picture that helps understanding the structure and properties difference between the crystalline and amorphous phases, thus paving the way for the development of new phase change alloys.

Raty J.-Y., Godlevsky V., Ghosez P., Bichara C., Gaspard J.-P., Chelikowsky J. R.,

Evidence of a reentrant Peierls distortion in liquid GeTe. Phys. Rev. Lett., 85, -9-, 1950-3, 2000.

Bergman C., Bichara C., Gaspard J.-P., Tsuchiya Y. Experimental investigation of the water-like density anomaly in liquid Ge15Te85 eutectic alloys. Phys. Rev. B67, 104202, 2003.

Coulet M.-V., Testemale D., Hazemann J.-L., Gaspard J.-P., Bichara C.,

A Reverse Monte Carlo analysis of the local order in liquid Ge.15 Te.85 alloys combining neutron scattering and X-Ray Absorption Spectroscopy. Phys. Rev. B, 72, 174209, 2005.

Bichara C., Johnson M., Raty J.-Y.,

Temperature-induced density anomaly in Te-rich liquid germanium tellurides: p versus sp3 bonding?

Phys. Rev. Lett., 95, 267801, 2005.

C. Bichara, M. Johnson, J.-P. Gaspard

Octahedral structure of liquid GeSb2Te4 alloy : first principles molecular dynamics study

Phys. Rev. B 75, 060201R, 2007.

 

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Related papers

Presentation: Oral at E-MRS Fall Meeting 2008, Symposium G, by Christophe Bichara
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-19 15:00
Revised:   2009-06-07 00:48