Resistance 1/F Noise due to the Motion of Hydrogen in Palladium and Amorphous PalladiumSilicon
Abstract
Measurements of the 1/f resistance noise due to the motion of hydrogen in polycrystalline palladium and amorphous Pd_{80}Si _{20} are described. The noise intensity S_{R}(f,T) is reported as a function of temperature T, hydrogen concentration X_{H}, and in some cases magnetic field H, for 3 K < T < 300 K, 0.15 < X_ {H} < 5 atomic%, and H < 3.2 Tesla. These measurements are used to test predictions of the dynamics and size of the 1/f resistance noise, based on a model of noise produced by defect motion. In pure Pd, S_{R}(f,T) is linearly proportional to X_{H} . At high temperatures, the resistance fluctuations have a distinctive spectrum and temperature dependence due to longrange diffusion of protons. The 1/f noise has a single, discrete peak at 120 K, establishing that the 1/f fluctuations are being produced by thermallyactivated atomicscale "hops" of the protons between interstitial sites in the Pd lattice. Measurement of the number of moving scatterers allows determination of the relative resistance fluctuation for one hop as delta r/r ~ 1/4, in agreement with applicable quantuminterference (QI) calculations for two point scatterers in the clean limit. In amorphous Pd_{80} Si_{20}, the 1/f noise exhibits two peaks as a function of temperature, one at 80 K and one which systematically shifts with X _{H} between 130 and 160 K. Both peaks correspond to thermallyactivated processes, with reasonable attempt times and activation energies for microscopic hops in the PdSi matrix. The peak at higher T is in quantitative agreement with Internal Friction measurements for absolute peak position, peak shift with X_ {H}, and relative peak height; deltar/r is about 1/2. Below T = 40 K, S _{R}(f,T) flattens, and exhibits a small dependence on magnetic field, both consistent with a dirty QI prediction for enhanced 1/f noise at low temperatures. Calculations are presented for the resistance fluctuation due to the motion of a point scatterer near dislocations and grain boundaries. The results are qualitatively similar to previous results for two point scatterers, including the fact that the resistance of the point scatterer and extended defect in proximity can be smaller than resistance of the two when isolated.
 Publication:

Ph.D. Thesis
 Pub Date:
 1989
 Bibcode:
 1989PhDT........33Z
 Keywords:

 Physics: Condensed Matter