Details

Autor(en) / Beteiligte

• Schlabach, S.
• Szabó, D. V.
• Vollath, D.
• de la Presa, P.
• Forker, M.

Titel

Structure and grain growth of Ti O 2 nanoparticles investigated by electron and x-ray diffractions and Ta 181 perturbed angular correlations

Ist Teil von

• Journal of applied physics, 2006-07, Vol.100 (2), p.024305-024305-9

Ort / Verlag

American Institute of Physics

Erscheinungsjahr

2006

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Bare and coated Ti O 2 nanoparticles with particle sizes d < 5 nm have been synthesized in a microwave plasma process. Structural properties of these materials have been investigated by transmission electron microscopy, x-ray diffraction, and perturbed angular correlation (PAC) measurements of the electric quadrupole interaction (QI) at the probe nucleus Ta 181 on the metal site of Ti O 2 at temperatures 290 ⩽ T ⩽ 1450 K . The electron diffraction of the uncoated nanoparticles in the as-synthesized state reflects long range order in the Ti sublattice. Depending on the particles size, either the anatase or the rutile phase of Ti O 2 was found. Anatase appears to be the stable form of nanocrystalline Ti O 2 below d ∼ 10 nm . The PAC spectra of these nanocrystalline oxides are characterized by a broad distribution of strong quadrupole interactions, indicating a strongly disordered oxygen environment of the metal sites. Upon annealing, the grain size grows from d < 5 nm after synthesis to d > 100 nm after 1300 K . PAC spectra taken in the same temperature range show that with increasing temperature, the initially disordered state transforms to well-ordered rutile Ti O 2 . The data suggest a critical grain size of d ∼ 10 nm for the onset of the ordering process. The spectra of coarse-grained Ti O 2 are reached at a particle size d ⩾ 30 nm . In n - Ti O 2 coated with Al 2 O 3 and Zr O 2 both the cores and the coatings were found to grow with increasing temperature; the cores of the coated particles, however, grow much less than those of the noncoated particles. The PAC method was used to investigate the QI in both Ti O 2 cores and in the Zr O 2 coating of n - Ti O 2 ∕ Zr O 2 at different temperatures. These data suggest that although the coated particles grow with temperature, the ordering process is obstructed, possibly by a solid state reaction between the Ti O 2 kernels and the coatings.