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Characterization of supercooled liquid Ge2Sb2Te5 and its crystallization by ultrafast-heating calorimetry
J.Orava1,2, A.L.Greer1, B.Gholipour3, D.W.Hewak3 and C.E.Smith4
1. Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK
2. Centre for Material Science, University of Pardubice, Studentska 95, 532 10 Pardubice, Czech Republic
3. Optoelectronics Research Centre, University of Southampton, UK
4. Mettler-Toledo, Beaumont Leys, Leicester LE4 1AW, UK.
Differential scanning calorimetry (DSC) is widely used to study the stability of amorphous solids, characterizing the kinetics of crystallization close to the glass-transition temperature Tg.We apply ultrafast DSC to the phase-change material Ge2Sb2Te5 (GST) and show that if the range of heating rates is extended to more than 104 K s-1, the analysis can cover a wider temperature range, up to the point where the crystal growth rate approaches its maximum. The growth rates that can be characterized are some four orders of magnitude higher than in conventional DSC, reaching values relevant for the application of GST as a data-storage medium. The kinetic coefficient for crystal growth has a strongly non-Arrhenius temperature dependence, revealing that supercooled liquid GST has a high fragility. Near Tg there is evidence for decoupling of the crystal-growth kinetics from viscous flow, matching the behaviour for a fragile liquid suggested by studies on oxide and organic systems.
Nature Materials (2012) Vol.11 pp.279-283
Copyright University of Southampton 2006