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

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

1,2,* , 1
 and 1
Received: 7 February 2012; in revised form: 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.
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 which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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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.

AMA 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(2):710-729.

Chicago/Turabian Style

Pivak, Yevheniy; Schreuders, Herman; Dam, Bernard. 2012. "Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range." Crystals 2, no. 2: 710-729.


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