Kenji Hashizume

Tracer diffusion coefficient of tritium in vanadium and trapping effect due to zirconium impurity

The tracer diffusion coefficient of tritium in the α-phase of vanadium is measured in a temperature region from 323 to 523 K by making use of the glow discharge implantation method recently developed by the present authors. The obtained results are in good agreement with the data previously reported by Qi et al. (J. Phys. F: Metal Phys. 13 (1983) 2053). The trapping effect of zirconium on the diffusion of hydrogen isotopes is examined by using specimens containing a small amount of zirconium impurity. The existence of at least two kinds of trapping sources is deduced by analyzing the concentration dependence of tracer diffusion coefficient of tritium: one is due to zirconium and the other is due to a certain complex of zirconium with interstitial impurities such as oxygen and nitrogen. Trapping energies of 0.15 and 0.36 eV are assigned to the former and the latter, respectively.

Hydrogen isotope electromigration and impurity effect in vanadium

Abstract The effective charge of protium and tritium in the α-phase of vanadium has been measured by means of a stationary state electromigration experiment in a temperature region from 323 to 523 K. The obtained results have shown a definite mass dependence such as Z * (T)> Z * (H) in a lower temperature region and a tendency that the effective charge of H and T approaches a same value in a higher temperature region. By comparing this result with the data for protium and deuterium previously reported by other investigators, we have concluded a mass dependence according to the sequence Z * (T)> Z * (D)> Z * (H) in a lower temperature region. The origins of this mass dependence has been discussed by decomposing the effective charge into the direct and wind charges. The trapping effect due to a small zirconium impurity in the investigated vanadium specimen on the electromigration of hydrogen isotopes has been also examined and the trapping model has been discussed.

Isotope dependence of the effective valence of protium and deuterium in the α phase of tantalum

Abstract The effective valence Z ∗ of protium and deuterium in the α phase of Ta has been measured by means of a stationary state electromigration experiment in the temperature region from 373 K to 523 K. A definite isotope dependence Z ∗( H ) > Z ∗ ( D ) has been found. The reversal of the isotope dependence to Z ∗ ( H ) Z ∗ ( D ) in the temperature region below 350 K has been suggested from the temperature dependence of Z ∗ . The direct valence Zd of H and D has been evaluated by relating the temperature dependence of Z ∗ to that of electric resistivity, leading to the values 1.7 and 0.91 respectively. We also found that the contribution of the wind valence Zw is negative and depends on the isotopes.

The direct force on electromigrating hydrogen isotopes

The present understanding of the magnitude of the direct force on hydrogen and its isotopes deuterium and tritium is discussed in the light of new experimental data and existing theoretical formulations. By this it is proven, that the direct valence of hydrogen can be significantly different from the unscreened jellium value of unity. Furthermore, a more detailed interpretation of a resistivity dependent direct valence is given, which clarifies the controversy around that subject. Selfconsistent calculations of the electronic charge density at and around an interstitial, at all positions along its electromigration jump path, are required to come to a more complete understanding of the measured results.

Correlation of mass dependence between heat of transport and effective charge of hydrogen isotopes in V, Nb and Ta

Abstract The experimental data of heat of transport Q * and effective charge Z * of protium, deuterium and tritium in vanadium, niobium and tantalum recently measured by the present authors are summarized for comparison. The data of Q * show a definite mass and element dependence whereas those of Z * do not show such a trend. Simple correlation of mass and element dependence between Q * and Z * is not found out by direct comparison of these data. Similarities of the atomistic origins between Q * and Z * are discussed, in particular the screening effect due to electrons is discussed by correlating the atomistic interpretation of the mass and element dependence of Q * with the interpretation of the direct charge.