scholarly journals Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material

2018 ◽  
Vol 4 (11) ◽  
pp. eaat8632 ◽  
Author(s):  
Shuai Wei ◽  
Zach Evenson ◽  
Moritz Stolpe ◽  
Pierre Lucas ◽  
C. Austen Angell
Keyword(s):  
Liquid Phase ◽  
Phase Change ◽  
Melting Temperature ◽  
Phase Change Materials ◽  
Dynamic Properties ◽  
Switching Behavior ◽  
Einstein Relation ◽  
Elastic Neutron ◽  
Phase Switching ◽  
Memory Applications

The dynamic properties of liquid phase-change materials (PCMs), such as viscosity η and the atomic self-diffusion coefficientD, play an essential role in the ultrafast phase switching behavior of novel nonvolatile phase-change memory applications. To connect η toD, the Stokes-Einstein relation (SER) is commonly assumed to be valid at high temperatures near or above the melting temperatureTmand is often used for assessing liquid fragility (or crystal growth velocity) of technologically important PCMs. However, using quasi-elastic neutron scattering, we provide experimental evidence for a breakdown of the SER even at temperatures aboveTmin the high–atomic mobility state of a PCM, Ge1Sb2Te4. This implies that although viscosity may have strongly increased during cooling, diffusivity can remain high owing to early decoupling, being a favorable feature for the fast phase switching behavior of the high-fluidity PCM. We discuss the origin of the observation and propose the possible connection to a metal-semiconductor and fragile-strong transition hidden belowTm.

scholarly journals Thermodynamics and kinetics of glassy and liquid phase-change materials

2021 ◽  
Vol 135 ◽  
pp. 106094
Author(s):  
Narges Amini ◽  
Julian Pries ◽  
Yudong Cheng ◽  
Christoph Persch ◽  
Matthias Wuttig ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Phase Change ◽  
Phase Change Materials ◽  
Thermodynamics And Kinetics ◽  
Kinetics Of

scholarly journals Scalability of Phase Change Materials in Nanostructure Template

2015 ◽  
Vol 2015 ◽  
pp. 1-4
Author(s):  
Wei Zhang ◽  
Biyun L. Jackson ◽  
Ke Sun ◽  
Jae Young Lee ◽  
Shyh-Jer Huang ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Scaling Limit ◽  
Phase Change Memory ◽  
Leakage Power ◽  
Memory Element ◽  
Transmission Electron ◽  
Diffraction Mode ◽  
Memory Applications ◽  
Change Memory

The scalability of In2Se3, one of the phase change materials, is investigated. By depositing the material onto a nanopatterned substrate, individual In2Se3nanoclusters are confined in the nanosize pits with well-defined shape and dimension permitting the systematic study of the ultimate scaling limit of its use as a phase change memory element. In2Se3of progressively smaller volume is heated inside a transmission electron microscope operating in diffraction mode. The volume at which the amorphous-crystalline transition can no longer be observed is taken as the ultimate scaling limit, which is approximately 5 nm3for In2Se3. The physics for the existence of scaling limit is discussed. Using phase change memory elements in memory hierarchy is believed to reduce its energy consumption because they consume zero leakage power in memory cells. Therefore, the phase change memory applications are of great importance in terms of energy saving.

scholarly journals Integral Solution of Two-Region Solid–Liquid Phase Change in Annular Geometries and Application to Phase Change Materials–Air Heat Exchangers

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4474 ◽  
Author(s):  
Hamidreza Shabgard ◽  
Weiwei Zhu ◽  
Amir Faghri
Keyword(s):  
Liquid Phase ◽  
Boundary Conditions ◽  
Phase Change ◽  
Phase Change Materials ◽  
Volume Fraction ◽  
Control Volume ◽  
Solid Volume Fraction ◽  
Solidification Time ◽  
Design And Optimization ◽  
Solid Liquid

A mathematical model based on the integral method is developed to solve the problem of conduction-controlled solid–liquid phase change in annular geometries with temperature gradients in both phases. The inner and outer boundaries of the annulus were subject to convective, constant temperature or adiabatic boundary conditions. The developed model was validated by comparison with control volume-based computational results using the temperature-transforming phase change model, and an excellent agreement was achieved. The model was used to conduct parametric studies on the effect of annuli geometry, thermophysical properties of the phase change materials (PCM), and thermal boundary conditions on the dynamics of phase change. For an initially liquid PCM, it was found that increasing the radii ratio increased the total solidification time. Also, increasing the Biot number at the cooled (heated) boundary and Stefan number of the solid (liquid) PCM, decreased (increased) the solidification time and resulted in a greater (smaller) solid volume fraction at steady state. The application of the developed method was demonstrated by design and analysis of a PCM–air heat exchanger for HVAC systems. The model can also be easily employed for design and optimization of annular PCM systems for all associated applications in a fraction of time needed for computational simulations.

Synthesis of novel solid–liquid phase change materials and electrospinning of ultrafine phase change fibers

2012 ◽  
Vol 96 ◽  
pp. 202-209 ◽  
Author(s):  
Changzhong Chen ◽  
Shanshan Liu ◽  
Wenmin Liu ◽  
Yiyang Zhao ◽  
Youzhi Lu
Keyword(s):  
Liquid Phase ◽  
Phase Change ◽  
Phase Change Materials ◽  
Solid Liquid
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