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Crystals 2012, 2(2), 710-729; doi:10.3390/cryst2020710

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

1
Materials for Energy Conversion and Storage (MECS), Faculty of Applied Sciences, Delft University of Technology, P.O. Box 5045, 2600GA Delft, The Netherlands
2
Department of Development & Engineering EUV S&C Sources, ASML, De Run 6501, 5504 DR, P.O. Box 324, 5500 AH Veldhoven, The Netherlands
*
Author to whom correspondence should be addressed.
Received: 7 February 2012 / Revised: 14 June 2012 / Accepted: 14 June 2012 / Published: 20 June 2012
(This article belongs to the Special Issue Hydrogen Storage Alloys)
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Abstract

Using hydrogenography, we investigate the thermodynamic parameters and hysteresis behavior in Mg thin films capped by Ta/Pd, in a temperature range from 333 K to 545 K. The enthalpy and entropy of hydride decomposition, ∆Hdes = −78.3 kJ/molH2, Sdes = −136.1 J/K molH2, estimated from the Van't Hoff analysis, are in good agreement with bulk results, while the absorption thermodynamics, ∆Habs = −61.6 kJ/molH2, ∆Sabs = −110.9 J/K molH2, appear to be substantially affected by the clamping of the film to the substrate. The clamping is negligible at high temperatures, T > 523 K, while at lower temperatures, T < 393 K, it is considerable. The hysteresis at room temperature in Mg/Ta/Pd films increases by a factor of 16 as compared to MgH2 bulk. The hysteresis increases even further in Mg/Pd films, most likely due to the formation of a Mg-Pd alloy at the Mg/Pd interface. The stress–strain analysis of the Mg/Ta/Pd films at 300–333 K proves that the increase of the hysteresis occurs due to additional mechanical work during the (de-)hydrogenation cycle. With a proper temperature correction, our stress–strain analysis quantitatively and qualitatively explains the hysteresis behavior in thin films, as compared to bulk, over the whole temperature range. View Full-Text
Keywords: hydrogenography; MgH2 thin films; thermodynamics; clamping; hysteresis; stress-strain model hydrogenography; MgH2 thin films; thermodynamics; clamping; hysteresis; stress-strain model
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Pivak, Y.; Schreuders, H.; Dam, B. Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range. Crystals 2012, 2, 710-729.

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