Quenching and electron-irradiation effects in orderedβ-PdH(D)0.63around the resistivity anomaly near 50 K

Abstract

P-PdH(D)063 specimens had been quenched across the 50-K anomaly and/or bombarded with electrons of 0.35 -0.8 MeV energy at 20 K. They exhibited after each treatment a residualresistivity decrease,hp, which annealed upon heating in the anomaly region. A kinetic analysis of the recovery process yielded an activation energy for H-defect migration of E (H, D) =50%15 meV for a first-order reaction. An investigation of the isotope-dependent radiation-inducedbp;"asa function of the electron energy led, by fitting theoretical collision cross sections, to a displacement threshold assimilated with a binding energy of hydrogen in its sublattice, Eb -0.01 eV, and to a defect resistivity, pdd = -6 pQ cm/unit concentration. The proposed defect configuration is occupational disorder in the hydrogen-vacancy sublattice, created by site interchange of H atoms with vacant octahedral sites of the Pd lattice, This leads to an effective redistribution of the Ni"Mo ( n = 1 -4) type rnicrodomains (Ni equivalent to H, Mo equivalent to H vacancy) as observed by neutron scattering in the anomaly region, by locally forming Ni"+lMo-type cells of different symmetry.

Hydrogen migration in electron irradiated Pd based dilute alloys around the 50 K anomaly

“…The resistivity change has been analyzed by the cross-cut method without using the value of the order of reaction used by them. The presently obtained results are compared with our results for the quenched specimens [2,3] and the results by Vajda et al [4].…”

“…It has been already clarified in previous investigations [1][2][3][4][5][6][7][8][9][10][11] that the electrical resistivities of Pd and Pd based-H(D) alloys increase by ordering of the hydrogen isotopes and decreases by disordering of the isotopes, though the behavior should be limited to the early stage of the ordering. Therefore, if the hydrogen atoms in the specimen disorder by electron irradiation, the resistivity of the specimen has to decrease.…”

“…They obtained smaller migration energies (about halves of ours) for hydrogen isotopes compared with our results of quenched materials. In the course of experiment, to clarify the cause of the disagreement between our results and the results of Vajda et al [4], we also obtained a value belonging to the category of large activation energies for fast cooled or 12 C ion irradiated Pd-H specimen using experimental methods [5] similar to that of Vajda et al [4].…”

“…Investigations of hydrogen migration due to the ordering of hydrogen isotopes have first been done by Vajda et al [4] for both fast cooled and/or electron irradiated specimens around 50 K range in Pd-H(D) alloys. They obtained smaller migration energies (about halves of ours) for hydrogen isotopes compared with our results of quenched materials.…”

“…In the present experiment, the disordered hydrogen atoms in charged Pd-1 at.% Fe and Pd-1 at.% Ag alloys have been produced by irradiation with 0.5 MeV electrons and the specimens have been annealed with a constant heating rate and the resistivity has been measured as a function of temperature as Vajda et al [4] have done. The resistivity change has been analyzed by the cross-cut method without using the value of the order of reaction used by them.…”