The '50K' transition in palladium-hydrogen alloys. I. Internal friction

Using a low frequency torsion pendulum, measurements have been made of the internal friction, Q-1, of some Pd-H alloys (0.54<or=H/Pd<or=0.7) over the temperature range 4-200K, with particular emphasis on exploring the effect that the transition near 50K has on Q-1. The authors observed a 'saw tooth' peak in Q-1 at approximately 50K, which has not previously been reported. From dependence of the character of this peak on the temperature and rate of change of temperature, and the absence of a frequency dependence for its temperature location, the authors infer, from a comparison with some other systems in which similar peaks have been seen, that it denotes the presence of an allotropic transformation at 50K. Relaxation behaviour associated with the 50K peak in Q-1, gives a relaxation time close to the longer relaxation time observed in spontaneous heat release experiments done in the laboratory with Pd-H near 50K.