Crystallite-size-dependent variations in the Raman spectrum of rutile TiO2 have been characterized and compared with those of the well-investigated rutile SnO2. For an average crystallite size below ∼25nm, the Raman spectrum of rutile TiO2 nanocrystals displays an additional low-frequency, possibly surface vibrational, mode at ∼105cm−1. The disorder-activated, high-frequency surface modes seen in the Raman spectrum of rutile SnO2 nanocrystals are absent. The Eg and A1g vibrational modes of rutile TiO2 show systematic redshifts, broadening, and intensity reductions with decreasing crystallite size, which are consistent with phonon confinement behavior. A phonon confinement model provides reasonable crystallite size quantification, as in the case of rutile SnO2 and RuO2.

Aluminum is considered to approach an "ideal" metal or free electron gas. The valence electrons move freely, as if unaffected by the presence of the metal ions. Therefore, the electron redistribution due to chemical bonding is subtle and has proven extremely difficult to determine. Experimental measurements and ab initio calculations have yielded substantially different results. We applied quantitative convergent-beam electron diffraction to aluminum to provide an experimental determination of the bonding electron distribution. Calculation of the electron distribution based on density functional theory is shown to be in close agreement. Our results yield an accurate quantitative correlation between the anisotropic elastic properties of aluminum and the bonding electron and electrostatic potential distributions.

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We characterized the size dependence of anatase TiO2 lattice parameters using Rietveld analysis of angle-dispersive synchrotron x-ray diffraction data obtained on a suite of nanocrystalline samples. The refined crystal structure and microstructure data suggest that for crystallites with size less than ∼10nm, the lattice parameters vary nonlinearly. Small lattice expansion, associated with possible increased Ti vacancy and lattice strain, at reduced crystallite size observed in our samples is in contrast to the lattice contraction behavior reported for “pure” anatase nanocrystals. The nonlinear, composition-dependent variation of anatase unit cell volume contrasts with the linear expansion behavior of rutile lattice at finite sizes.

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