Search

Doping ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ with Ti stabilizes the corundum paramagnetic metallic phase and restricts the transition to the monoclinic antiferromagnetic insulating phase at lower temperatures. In this study, we investigated the dependence of phase stability on Ti concentration for ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ nanocrystals as small as 20 nm. Ti doping of several percent induces a high-temperature insulating phase preserving the magnetic transition without the crystal symmetry change. The emergence of the insulating phases, which are peculiar to this crystal size, can be attributed to the enhancement of the on-site Coulomb interaction $U$ and increased mixing between ${a}_{1g}$ and ${e}_{g}^{\ensuremath{\pi}}$ states accompanied by characteristic lattice parameter changes in the high Ti doping region.

Nanocrystalline Ni can adopt a hexagonal close-packed (hcp) structure,which does not appear in a bulk form under any conditions.Structural studies found its $>$ 20% expansion of volume per atom compared with face-centered cubic (fcc) Ni.Hard x-ray photoemission spectroscopy of the hcp phase revealed a $>$ 0.14 valence electron transfer from 3$d$ to 4$s$ and 4$p$ orbitals and a 0.25 eV reduction in band energy per electron compared with the fcc phase.Its nonmagnetic nature was attributed to a low density of states at the Fermi level.Thermodynamic stability of the hcp phase can be explained by the band energy gain and the electrostatic potential energy loss as related to the large lattice expansion., 6 pages, 5 figures