| Abstract
| - We report the first measurements of elastic modulus and energy dissipation in Ti-doped and undoped sodiumaluminum hydride. It is shown that the chemical reactions that occur by varying the sample temperatures orby aging most sensitively affect the elastic constants, such that the modulus variations allow the time andtemperature evolution of decomposition to be monitored. After a well-defined thermal treatment at 436 K, athermally activated relaxation process appears at 70 K in the kilohertz range, denoting the existence of a newspecies, likely involving hydrogen, having a very high mobility, that is, 103 jumps/s at the peak temperaturecorresponding to a relaxation rate of about 1011 s-1 at room temperature. The activation energy of the processis 0.126 eV and the preexponential factor 7 × 10-14 s, which is typical of point defect relaxation. The peakis very broad with respect to a single Debye process, indicating strong interaction or/and multiple jumpingtype of the mobile entity. The present data suggest that the models aiming at interpreting the decompositionreactions and kinetics should take into account the indicated point-defect dynamics and stoichiometry defects.
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