Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

Science ◽  
2019 ◽  
Vol 364 (6445) ◽  
pp. 1062-1067 ◽  
Author(s):  
Peter Zalden ◽  
Florian Quirin ◽  
Mathias Schumacher ◽  
Jan Siegel ◽  
Shuai Wei ◽  
...  
Keyword(s):  
Phase Transition ◽  
Liquid Phase ◽  
Phase Change ◽  
Phase Change Materials ◽  
Crystallization Process ◽  
Pair Correlation ◽  
Atomic Scale ◽  
X Ray Diffraction ◽  
Liquid Phase Transition ◽  
X Ray

In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid–liquid phase transition in the phase-change materials Ag4In3Sb67Te26 and Ge15Sb85 at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics.

Femtosecond solid-liquid phase transition studied with ultrafast x-ray diffraction

2001 ◽  
Author(s):  
S. Fourmaux ◽  
Antoine Rousse ◽  
Christian Rischel ◽  
Ingo Uschmann ◽  
Stephane Sebban ◽  
...  
Keyword(s):  
Phase Transition ◽  
Liquid Phase ◽  
X Ray Diffraction ◽  
Liquid Phase Transition ◽  
X Ray ◽  
Solid Liquid

Molecular Reorientation in the Plastic Crystalline Phase of Tris

1979 ◽  
Vol 32 (4) ◽  
pp. 905 ◽  
Author(s):  
RE Wasylishen ◽  
PF Barron ◽  
DM Doddrell
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molecular Reorientation ◽  
Liquid Phase Transition ◽  
X Ray ◽  
Spin Lattice

Carbon-13 N.M.R. spectra of tris(hydroxymethyl)aminomethane (Tris) have been measured between 407 and 461 K. Proton-decoupled 13C N.M.R. spectra of solid Tris between 407 K and its melting point are relatively sharp (v� < 30 Hz) indicating rapid overall molecular reorientation in this temperature range. It was not possible to detect a 13C N.M.R, signal for Tris below 407 K. The observed 13C N.M.R. spin-lattice relaxation times appear continuous across the solid ↔ liquid phase transition. From the temperature dependence of T1, a rotational activation energy of 51.6 � 6 kJ mol-1 is calculated, which indicates that the molecules must expend considerable energy in reorienting. The N.M.R. results are discussed in relation to previous differential scanning calorimetry and X-ray diffraction data which indicate that Tris undergoes a solid ↔ solid transition at 407 K.

scholarly journals Crystal structure of the high-P polymorph of Ca2B6O6(OH)10·2(H2O) (meyerhofferite)

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Davide Comboni ◽  
Tomasz Poreba ◽  
Francesco Pagliaro ◽  
Tommaso Battiston ◽  
Paolo Lotti ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Large Volume ◽  
Atomic Scale ◽  
Deformation Mechanisms ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Structural Differences

The crystal structure of the high-pressure polymorph of meyerhofferite, ideally Ca2B6O6(OH)10·2(H2O), has been determined by means of single-crystal synchrotron X-ray diffraction data. Meyerhofferite undergoes a first-order isosymmetric phase transition to meyerhofferite-II, bracketed between 3.15 and 3.75 GPa, with a large volume discontinuity. The phase transition is marked by an increase in the coordination number of the boron B1 site, from III to IV, leading to a more interconnected and less compressible structure. The main structural differences between the two polymorphs and the P-induced deformation mechanisms at the atomic scale are discussed.

Crystallization Characteristics of Ge-Sb Phase Change Materials

2009 ◽  
Vol 1160 ◽  
Author(s):  
Simone Raoux ◽  
Cyril Cabral ◽  
Lia Krusin-Elbaum ◽  
Jean L. Jordan-Sweet ◽  
Martin Salinga ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Mass Density ◽  
Large Change ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Time Resolved ◽  
X Ray ◽  
Diffraction Peaks ◽  
Low X

AbstractThe crystallization behavior of Ge-Sb phase change materials with variable Ge:Sb ratio X between 0.079 and 4.3 was studied using time-resolved x-ray diffraction, differential scanning calorimetry, x-ray reflectivity, optical reflectivity and resistivity vs. temperature measurements. It was found that the crystallization temperature increases with Ge content from about 130 °C for X = 0.079 to about 450 °C for X = 4.3. For low X, Sb x-ray diffraction peaks occurred during a heating ramp at lower temperature than Ge diffraction peaks. For X = 1.44 and higher, Sb and Ge peaks occurred at the same temperature. Mass density change upon crystallization and optical and electrical contrast between the phases show a maximum for the eutectic alloy with X = 0.17. The large change in materials properties with composition allows tailoring of the crystallization properties for specific application requirements.

Investigation of Phase Transition in Stacked Ge-Chalcogenide/SnTe Phase-change Memory Films

2007 ◽  
Vol 1056 ◽  
Author(s):  
Feiming Bai ◽  
Surendra Gupta ◽  
Archana Devasia ◽  
Santosh Kurinec ◽  
Morgan Davis ◽  
...  
Keyword(s):  
Phase Transition ◽  
Solid Solution ◽  
Phase Change ◽  
Phase Change Memory ◽  
Thin Layers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Area Detector ◽  
Memory Applications ◽  
Change Memory

ABSTRACTPhase transitions in stacked GeTe/SnTe and Ge2Se3/SnTe thin layers for potential phase-change memory applications have been investigated by X-ray diffraction using a two-dimensional area detector system. The as-deposited underlying GeTe or Ge2Se3 layer is amorphous, whereas the top SnTe layer is crystalline. In the GeTe/SnTe stack, the crystallization of GeTe phase occurs near 170°C, and upon further heating, the GeTe phase disappears, followed by the formation of rocksalt-structured GexSn1−xTe solid solution. In the Ge2Se3/SnTe stack, the phase transition starts with the separation of a SnSe phase due to the migration of Sn ions into the Ge2Se3 layer. SnSe is believed to facilitate the crystallization of Ge2Se3-SnTe solid solution at ∼360°C, which is much lower than the crystallization temperature of Ge2Se3, therefore consuming less power during the phase transition.

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