An ultrasonic study of stress-induced ordering of hydrogen in single-crystal palladium hydride

Publisher Website
Google Scholar
Abstract
The attenuation of longitudinal acoustic waves propagating along the (110) axis in single-crystal PdH0.64 has been investigated over the temperature range 80-300K and the frequency range 10-270 MHz. At a given frequency the attenuation exhibits a maximum as a function of temperature. The attenuation peaks are attributed to the stress-induced ordering of hydrogen atoms on the interstitial sites. These peaks occur when omega tau R=1, where omega /2 pi is the frequency of the ultrasonic wave and tau R is the relaxation time for stress-induced ordering. An Arrhenius plot of tau R-1 against inverse temperature gives an activation energy of 0.23+or-0.02 eV over the temperature range 190-240K, approximately the same as that deduced by other techniques for the hopping of hydrogen between interstitial sites. Surprisingly, the experimental value of tau R at any particular temperature is about an order of magnitude shorter than the mean time of stay of hydrogen on an interstitial site as determined by other experimental techniques. Possible reasons for this discrepancy are discussed.