Interaction of trapped hydrogen with dislocations at low-temperature in deformed palladium

Segregation of solute atoms to dislocations occurs due to the elastic interaction with the hydrostatic stress of edge dislocations and also due to the dislocation core-solute interaction. The characteristics of the local segregation at dislocations, Cottrell atmosphere, at low temperature and low concentration have not been investigated until the phase transformation of the deformed PdH0.0008 was recently observed at low temperature. The purpose of this study was to investigate the phase behavior of the trapped solute influenced by the distorted dislocation environment.;The phase behavior of the Cottrell atmosphere in deformed Pd was investigated as a function of temperature by incoherent inelastic neutron scattering (IINS) and small angle neutron scattering (SANS) measurements. The IINS measurements of the deformed PdH0.00134 presented the characteristic vibrational density-of-states (VDOS) of hydrogen trapped at dislocation, while the spatial profile of the trapped hydrogen in the deform PdH0.00134 was determined by the SANS measurements.;The VDOS of hydrogen in the deformed PdH0.00134 was obtained at 4, 100, 200, and 295 K by the IINS measurements. The VDOS at 4 K exhibited the primary peak of approximately 57 meV associated with hydrogen-rich beta-Pd hydride phase. The characteristic peak of the VDOS at 295 K corresponded to dilute solid-solution beta-Pd hydride phase, appearing at approximately 68 meV. Coexistence of the beta-phase and the alpha-phase was observed at 100 and 200 K. This suggests that hydrogen trapped at dislocations undergoes the phase transformation upon temperature change from 295 to 4 K in the deformed PdH0.00134.;The spatial characterization of the Cottrell atmosphere was performed by the SANS measurements at 15, 100, and 200 K. The cylindrical geometry with the radius of 9 and the length of 50 was obtained and the dislocation density was 1.2x10-11 cm-2. Based on the spatial profile, the local concentration of the trapped hydrogen was estimated as approximately 0.2 [H]/[Pd] even at 200 K, which exceeds the dilute solid-solution regime (∼0.01 [H]/[Pd] at room temperature). Correlation between the local concentration and the phase behavior verified the condensation of the hydrogen-rich phase along the dislocations.;Given such low hydrogen concentration in the heavily deformed Pd, this behavior is representative of hydrogen trapped at dislocations at low temperature. Correlating the spatial and the vibrational characterization of the Cottrell atmosphere demonstrated the phase behavior of the trapped solute interacting with dislocations at the distorted dislocation environment.