Role of activation energy in resistance drift of amorphous phase change materials

Relaxation processes are decisive for many physical properties of amorphous materials. For amorphous phase-change materials (PCMs) used in nonvolatile memories, relaxation processes are, however, difficult to characterize because of the lack of bulk samples. Here, instead of bulk samples, we use powder mechanical spectroscopy for powder samples to detect the prominent excess wings—a characteristic feature of β-relaxations—in a series of amorphous PCMs at temperatures below glass transitions. By contrast, β-relaxations are vanishingly small in amorphous chalcogenides of similar composition, which lack the characteristic features of PCMs. This conclusion is corroborated upon crossing the border from PCMs to non-PCMs, where β-relaxations drop substantially. Such a distinction implies that amorphous PCMs belong to a special kind of covalent glasses whose locally fast atomic motions are preserved even below the glass transitions. These findings suggest a correlation between β-relaxation and crystallization kinetics of PCMs, which have technological implications for phase-change memory functionalities.

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Role of Phase Change Materials Containing Carbonized Rice husks on the Roof-Surface and Indoor Temperatures for Cool Roof System Application

Molecules ◽

10.3390/molecules25143280 ◽

2020 ◽

Vol 25 (14) ◽

pp. 3280

Author(s):

Hong Gun Kim ◽

Yong-Sun Kim ◽

Lee Ku Kwac ◽

Mira Park ◽

Hye Kyoung Shin

Keyword(s):

Thermal Conductivity ◽

Phase Change ◽

Phase Change Materials ◽

Paraffin Wax ◽

Heat Absorption ◽

Rice Husks ◽

Indoor Temperature ◽

Cool Roof ◽

Plastic Composites

This study researches the effect of phase change materials (PCMs) containing carbonized rice husks (CRHs) in wood plastic composites (WPCs) as roof finishing materials on roof-surface and indoor temperatures. A cool roof miniature model was prepared, and measurements were taken using three fixed temperatures of 30 to 32 °C, 35 to 37 °C, and 40 to 42 °C. Sodium sulfate decahydrate (Na2SO4·10H2O) and paraffin wax were selected as the PCMs. CRHs were used as additives to improve the thermal conductivities of the PCMs. At lower fixed temperatures such as 30 to 32 °C and 35 to 37 °C, the rates of increase of the surface temperatures of roofs containing CRHs with Na2SO4·10H2O, and paraffin wax, were observed to gradually decrease compared to those of the roofs without PCMs. The indoor temperatures for the above-mentioned PCMs containing CRHs were maintained to be lower than those of the indoors without PCMs. Additionally, as the CRH content in the PCM increased, the rates of increase of the roof-surface and indoor temperatures decreased due to a faster roof heat absorption by PCMs through the improved thermal conductivity of CRHs. However, under higher artificial temperatures such as 40 to 42 °C, Na2SO4·10H2O with CRHs exhibited no effect due to being out of latent heat range of Na2SO4·H2O. For paraffin wax, as CRH content increased, their roof- surface and indoor temperatures decreased. Especially, the surface temperature of the roof containing paraffin contained 5 wt.% CRHs reduced by 11 °C, and its indoor temperature dropped to 26.4 °C. The thermal conductivity of PCM was enhanced by the addition of CRHs. A suitable PCM selection in each location can result in the reduction of the roof-surface and indoor temperatures.

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Defects in amorphous phase-change materials

Journal of Materials Research ◽

10.1557/jmr.2013.72 ◽

2013 ◽

Vol 28 (9) ◽

pp. 1139-1147 ◽

Cited By ~ 28

Author(s):

Jennifer Luckas ◽

Daniel Krebs ◽

Stephanie Grothe ◽

Josef Klomfaß ◽

Reinhard Carius ◽

...

Keyword(s):

Phase Change ◽

Amorphous Phase ◽

Phase Change Materials ◽

Image Position

Abstract

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◾ A Role of Phase Change Materials in Building Applications

Energy Security and Sustainability ◽

10.1201/9781315368047-13 ◽

2016 ◽

pp. 131-152

Keyword(s):

Phase Change ◽

Phase Change Materials

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Exploring the limits of fast phase change materials

MRS Proceedings ◽

10.1557/proc-674-v1.3 ◽

2001 ◽

Vol 674 ◽

Cited By ~ 8

Author(s):

Han-Willem Wöltgens ◽

Ralf Detemple ◽

Inés Friedrich ◽

Walter K. Njoroge ◽

Ingo Thomas ◽

...

Keyword(s):

Activation Energy ◽

Phase Change ◽

Phase Change Materials ◽

Ternary Alloys ◽

Electrical Measurements ◽

Material Synthesis ◽

Fast Phase ◽

Chalcogenide Alloys ◽

Speed Up ◽

Critical Nuclei

ABSTRACTIn the last decade a number of chalcogenide alloys, including ternary alloys of GeSbTe and quaternary alloys of InAgSbTe, have been identified which enable fast phase change recording. In the quest for materials with improved phase change kinetics we present two different approaches. By comparing alloys with well-defined stoichiometries the mechanisms which govern the transformation kinetics are determined. Optical and electrical measurements determine the activation energy for crystallization to 2.24 ± 0.11 eV for Ge2Sb2Te5 and to 3.71 ± 0.07 eV for Ge4Sb1Te5, respectively. It is shown that for GeSbTe-alloys with different composition the activation energy increases linearly with increasing Ge content. Power-time- reflectivity change diagrams recorded with a static tester reveal that Ge2Sb2Te5, in agreement with previous data, recrystallizes by the growth of sub critical nuclei, while Ge4Sb1Te5 grows from the crystalline rim surrounding the bit.To speed up the search for faster materials we employ concepts of combinatorial material synthesis by producing films with a stoichiometry gradient. Then laterally resolved secondary neutral mass spectroscopy (SNMS) combined with the static tester are used to identify the composition with superior properties for phase change applications.

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