The bonding of atomic oxygen on Pt(111) and Rh(111) was examined using density functional theory in order to understand their different chemical properties. The oxygen-surface interactions were modeled by bonding atomic oxygen to 10-atom clusters of Pt and Rh designed to model the (111) surface. Density functional theory was applied using the local density and generalized gradient approximations; results were obtained for both double-and triple-basis sets. Optimized geometries and binding energies were computed and favorably compared to available experimental values. Interestingly, the ionic bonding in the two cases is nearly the same, based on the similarities in the charge on oxygen. The Hirshfeld charges on oxygen were -0.225 and -0.207 for Rh 10 -O and Pt 10 -O , respectively, using the double-basis set. A more detailed analysis of the covalent bonding using crystal orbital overlap populations indicated that the 2p orbitals of oxygen interact in a greater bonding fashion with both the sp and d orbitals of Rh than with those of Pt. Additional calculations with adsorbed hydroxyl on these metal clusters show differences in covalent bonding similar to that of oxygen. In this case, however, differences in ionic bonding play a role; oxygen in hydroxyl has a greater charge on Pt than Rh. This leads to smaller differences in the interaction energies of hydroxyl on Rh and Pt compared with oxygen, resulting in differences in chemical reactivity between the two metals, especially with respect to reactions involving hydrogen transfer.

No abstract

Dy films, deposited on the surface of sintered Nd-Fe-B magnets by magnetron sputtering, were employed for grain boundary diffusion source. High coercivity sintered Nd-Fe-B magnets were successfully prepared. Effects of sputtering power and grain boundary diffusion processes (GBDP) on the microstructure and magnetic properties were investigated in detail. The dense and uniform Dy films were beneficial to prepare high coercivity magnets by GBDP. The maximum coercivity value of 1189 kA m −1 could be shown, which was an amplification of 22.3%, compared with that of as-prepared Nd-Fe-B magnet. Furthermore, the improved remanence and maximum energy product were also achieved through tuning grain boundary diffusion processes. Our results demonstrated that the formation of (Nd, Dy) 2 Fe 14 B shell surrounding Nd 2 Fe 14 B grains and fine, uniform and continuous intergranular RE-rich phases jointly contribute to the improved coercivity.

Ribbons of the Pr4.5Fe77B18.5 alloys were produced by melt spinning and then annealed by flash or conventional annealing to develop enhanced-remanence nanocrystalline magnetic material. These materials were studied by magnetic measurements, x-ray, and neutron diffraction. Curie temperature measurements show that the phases present are Pr2Fe14,B Fe3B, α-Fe, and Pr2Fe23B3. Rietveld analyses of the neutron and the x-ray diffraction spectra showed that the main phases of these materials were Pr2Fe14B and Fe3B, Pr2Fe14B being the major phase (≈60%). Differences between the values of the lattice parameters of Pr2Fe14B in these materials may indicate that this phase is not stoichiometric.