TY  - JOUR
A1  - Zalden, Peter
A1  - Quirin, Florian
A1  - Schumacher, Mathias
A1  - Siegel, Jan
A1  - Wei, Shuai
A1  - Koc, Azize
A1  - Nicoul, Matthieu
A1  - Trigo, Mariano
A1  - Andreasson, Pererik
A1  - Enquist, Henrik
A1  - Shu, Michael J.
A1  - Pardini, Tommaso
A1  - Chollet, Matthieu
A1  - Zhu, Diling
A1  - Lemke, Henrik
A1  - Ronneberger, Ider
A1  - Larsson, Jörgen
A1  - Lindenberg, Aaron M.
A1  - Fischer, Henry E.
A1  - Hau-Riege, Stefan
A1  - Reis, David A.
A1  - Mazzarello, Riccardo
A1  - Wuttig, Matthias
A1  - Sokolowski-Tinten, Klaus
T1  - Femtosecond x-ray diffraction reveals a liquid-liquid phase transition in phase-change materials
JF  - Science
N2  - 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.
Y1  - 2019
U6  - https://doi.org/10.1126/science.aaw1773
SN  - 0036-8075
SN  - 1095-9203
VL  - 364
IS  - 6445
SP  - 1062
EP  - 1067
PB  - American Assoc. for the Advancement of Science
CY  - Washington, DC
ER  - 
TY  - GEN
A1  - Spiekermann, Georg
A1  - Harder, M.
A1  - Gilmore, Keith
A1  - Zalden, Peter
A1  - Sahle, Christoph J.
A1  - Petitgirard, Sylvain
A1  - Wilke, Max
A1  - Biedermann, Nicole
A1  - Weis, Thomas
A1  - Morgenroth, Wolfgang
A1  - Tse, John S.
A1  - Kulik, E.
A1  - Nishiyama, Norimasa
A1  - Yavaş, Hasan
A1  - Sternemann, Christian
T1  - Persistent Octahedral Coordination in Amorphous GeO₂ Up to 100 GPa
by Kβ'' X-Ray Emission Spectroscopy
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - We measure valence-to-core x-ray emission spectra of compressed crystalline GeO₂ up to 56 GPa and of amorphous GeO₂ up to 100 GPa. In a novel approach, we extract the Ge coordination number and mean Ge-O distances from the emission energy and the intensity of the Kβ'' emission line. The spectra of high-pressure polymorphs are calculated using the Bethe-Salpeter equation. Trends observed in the experimental and calculated spectra are found to match only when utilizing an octahedral model. The results reveal persistent octahedral Ge coordination with increasing distortion, similar to the compaction mechanism in the sequence of octahedrally coordinated crystalline GeO₂ high-pressure polymorphs.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 699 
KW  - rutile-type
KW  - glass
KW  - crystalline
KW  - pressures
KW  - complexes
KW  - silicon
KW  - oxygen
KW  - SIO₂
KW  - MO
KW  - CU
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-427755
SN  - 1866-8372
IS  - 699
ER  - 
TY  - JOUR
A1  - Spiekermann, Georg
A1  - Harder, M.
A1  - Gilmore, Keith
A1  - Zalden, Peter
A1  - Sahle, Christoph J.
A1  - Petitgirard, Sylvain
A1  - Wilke, Max
A1  - Biedermann, Nicole
A1  - Weis, Thomas
A1  - Morgenroth, Wolfgang
A1  - Tse, John S.
A1  - Kulik, E.
A1  - Nishiyama, Norimasa
A1  - Yavaş, Hasan
A1  - Sternemann, Christian
T1  - Persistent Octahedral Coordination in Amorphous GeO₂ Up to 100 GPa
by Kβ'' X-Ray Emission Spectroscopy
JF  - Physical Review X
N2  - We measure valence-to-core x-ray emission spectra of compressed crystalline GeO₂ up to 56 GPa and of amorphous GeO₂ up to 100 GPa. In a novel approach, we extract the Ge coordination number and mean Ge-O distances from the emission energy and the intensity of the Kβ'' emission line. The spectra of high-pressure polymorphs are calculated using the Bethe-Salpeter equation. Trends observed in the experimental and calculated spectra are found to match only when utilizing an octahedral model. The results reveal persistent octahedral Ge coordination with increasing distortion, similar to the compaction mechanism in the sequence of octahedrally coordinated crystalline GeO₂ high-pressure polymorphs.
KW  - rutile-type
KW  - glass
KW  - crystalline
KW  - pressures
KW  - complexes
KW  - silicon
KW  - oxygen
KW  - SIO₂
KW  - MO
KW  - CU
Y1  - 2019
U6  - https://doi.org/10.1103/PhysRevX.9.011025
SN  - 2469-9926
SN  - 0556-2791
SN  - 1050-2947
SN  - 1094-1622
VL  - 9
IS  - 1
PB  - American Physical Society by the American Institute of Physics
CY  - Melville, NY
ER  -