Secondary electron emission measurement from Cr and Cu bombarded by an Ne10+ beam at 6 MeV/n

Backward secondary-electron-emission yield ($\delta$) from plates of 0.1 mm-thick Cu and 1 mm Cr and Al have been measured by irradiation of a fully stripped Ne$^{10+}$ beam at 6 MeV/$n$ stopped within each plate. A difference between $\delta$s from Cr and Cu larger than the ambiguity of this measurement ($\pm$3%) has been observed, with the discrepancy of the predicted small difference by kinetic emission based on stopping power and work function of each metal. The measured $\delta$ from Cr is larger than that from Cu, and also than previous measurements of other transition metals of the 3$d$ series, not only for the process of potential emission but also for kinetic. The conduction-electron density of states around the Fermi level calculated for the metals shows that the number of electrons just below the Fermi level and excited over it to an empty level by many kinds of reaction with the beam irradiation has to be considered. The number involved in this emission from Cr thus seems to be much larger than from Cu, which explains the relation of magnitudes for $\delta$. The measured $\delta$ from Al is larger than previous results, but is still consistent due to the existence of Al$_2$O$_3$ on the Al.

Local minimum in pair potentials of polyvalent metals: A limitation of pseudopotential theory

Local minimum appearing in the interionic pair potentials, when derived from local model pseudopotential, for Al (and some other polyvalent metals) remains as a long standing problem of clear understanding of its origin, although some attempts have been made by a few authors. The origin of this feature of local minimum is systematically investigated for the first time in this paper considering both the core size and the conduction electron density as variables. Interionic pair potential is derived from Ashcroft’s empty core model because it depends on these two variables only. Results of this investigation show monovalent metals do not exhibit a local minimum at all but trivalent Al and some other polyvalent metals do exhibit at their normal densities. Here, the combined effect of the core size and the conduction electron density results whether the local minimum will appear or not. More interestingly, for smaller core size, conduction electron density plays major role and for larger core size the core radius plays the major role in determining the depth of the local minimum.

Verteilung und Valenz der Kationen in Spinellsystemen mit Eisen und Vanadium, VIII / Distribution and Valence of the Cations in Spinel Systems with Iron and Vanadium, VIII

From lattice constants and Mössbauer data the valence distribution and an energy-level diagram of the spinel system Fe(FexV2-x)O4 have been derived. In the range 0.3 ≦ χ ≦ 1.5 the transition from normal to inverse spinels takes place. The Mößbauer spectra with 1.0 ≦ χ ≦ 2.0 consist of two sets of sextets corresponding to tetrahedral and octahedral sites. Typical values of isomer shift and internal magnetic field strength due to the different environments of the iron ion result from the superimposed sextets of the octahedral site pattern. Neighbouring V ions enhance the conduction electron density and diminish the strength of the magnetic interaction. Mößbauer data, Seebeck coefficients and activation energies lead to a model of both tetrahedral and octahedral conduction based on charge hopping. For Fe1,9V1,1 O4 there exists only one iron species.