scholarly journals Role of vacancies in metal–insulator transitions of crystalline phase-change materials

2012 ◽  
Vol 11 (11) ◽  
pp. 952-956 ◽  
Author(s):  
W. Zhang ◽  
A. Thiess ◽  
P. Zalden ◽  
R. Zeller ◽  
P. H. Dederichs ◽  
...  
Keyword(s):  
Phase Change ◽  
Crystalline Phase ◽  
Phase Change Materials ◽  
Metal Insulator

scholarly journals Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Valeria Bragaglia ◽  
Fabrizio Arciprete ◽  
Wei Zhang ◽  
Antonio Massimiliano Mio ◽  
Eugenio Zallo ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Random Access ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Insulator Transition ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Reversible Transformation ◽  
Vacancy Ordering

Abstract Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows.

scholarly journals The role of phase change materials for the sustainable energy

2016 ◽  
Vol 10 ◽  
pp. 00068 ◽  
Author(s):  
Marta Kuta ◽  
Dominika Matuszewska ◽  
Tadeusz Michał Wójcik
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Sustainable Energy

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

Molecules ◽  
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.

scholarly journals The Role of H-bonding in Phase Change Materials

2019 ◽  
Author(s):  
Karolina Matuszek ◽  
R. Vijayaraghavan ◽  
Mega Kar ◽  
Douglas Macfarlane
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Hirshfeld Surface ◽  
Industrial Processes ◽  
Heat Of Fusion ◽  
Organic Salts ◽  
Promising Alternative

Phase change materials (PCMs) which melt in the temperature range of 100-230 °C, are a promising alternative for the storage of thermal energy. In this range, large amounts of energy available from solar-thermal, or other forms of renewable heat, can be stored and applied to domestic or industrial processes, or to an Organic Rankine Cycle (ORC) engine to generate electricity. The amount of energy absorbed is related to the latent heat of fusion (ΔH<sub>f</sub>) and is often connected to the extent of hydrogen bonding in the PCM. Herein, we report fundamental studies, including crystal structure and Hirshfeld surface analysis, of a family of guanidinium organic salts that exhibit high values of ΔH<sub>f</sub>, demonstrating that the presence and strength of H-bonds between ions plays a key role in this property.

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