%0 Journal Article
%T Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range
%A Yevheniy Pivak
%A Herman Schreuders
%A Bernard Dam
%J Crystals
%D 2012
%I MDPI AG
%R 10.3390/cryst2020710
%X 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, £¿ H des = £¿78.3 kJ/molH 2, £¿ S des = £¿136.1 J/K molH 2, estimated from the Van't Hoff analysis, are in good agreement with bulk results, while the absorption thermodynamics, £¿ H abs = £¿61.6 kJ/molH 2, £¿ S abs = £¿110.9 J/K molH 2, 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 MgH 2 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¨Cstrain analysis of the Mg/Ta/Pd films at 300¨C333 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¨Cstrain analysis quantitatively and qualitatively explains the hysteresis behavior in thin films, as compared to bulk, over the whole temperature range.
%K hydrogenography
%K MgH2 thin films
%K thermodynamics
%K clamping
%K hysteresis
%K stress-strain model
%U http://www.mdpi.com/2073-4352/2/2/710