Mechanism of Inhibition of Nanoparticle Growth and Phase
Transformation by Surface Impurities
Online auxiliary material of the main article in PRL
Bin Chen1*, Hengzhong Zhang1, Benjamin Gilbert2, and Jillian F. Banfield1,2
1
2
Earth and Planetary Science, University of California-Berkeley, Berkeley, CA 94720
Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
*
To whom correspondence should be addressed. E-mail: binchen@berkeley.edu
PACS numbers: 68.03.Cd, 68.47.Jn, 64.70.Nd, 61.10.Ht, 61.10.-i
Estimation of yttrium surface site coverage:
It is unlikely that clusters of elemental Y are present at the surface because yttrium is
very reactive towards oxygen (the heat of formation of yttrium oxide is around -650
kJ/mol O, even more negative than that of TiO2 [S1]). Based on the number density of Ti
on different lattice planes and an assumed equal probability of surface exposure for (110),
(101), and (011) planes, the fraction of the atoms at the nanoparticle surface is
proportional to 1.25/d [S2]. The initial size of our TiO2 nanoparticles is about 6 nm, so
the fraction of atoms at the surface is ~21%. Considering the Y:O ratio (1.2:200) in our
samples and taking average coordination number as 5, about 15% of the surface oxygen
sites are bound to Y.
MD simulation:
The MD simulation was conducted for a 4 nm diameter particle rather than for a 6 nm
diameter particle, as used in the experiments, to ensure that the computation was feasible.
The atomic interaction functions given by Matsui and Akaogi were chosen for TiO2 [S3].
This set of potential functions has been previously shown to well reproduce the lattice
parameters, bulk modulii and other physical properties of the polymorphs of TiO2 [S4].
For the yttrium-oxygen interaction in anatase, we have chosen the interatomic potential
function designed by Lewis and Catlow for use in ionic oxides and mixed oxides [S5].
The initial configuration was constructed as follows: A 4nm anatase particle was cut from
the coordinates of bulk anatase, and then 16 randomly chosen Ti atoms on the near
surface layer were substituted by 16 Y atoms. While assuming no clustering of yttrium
atoms, the whole nanoparticle was made neutral by removing extra O or Ti atoms,
resulting in the MD particle containing 16 Y, 990 Ti and 2004 O atoms (i.e. molar Y:Ti =
1.6 %). The MD simulation was carried out in a canonical assemble (constant number of
atoms, volume, and temperature) at 300 K, with a time step of 0.01 fs for a length of 63
ps. At this MD timescale, the nanoparticle was fully structurally relaxed to a low-energy
state.
Figure S1 (Color online): Fourier transform magnitude of k3-weighted Y K-edge
EXAFS spectra of yttrium-doped TiO2 nanoparticles as a function of treatment
temperature. Inset: A representative one of the k3-weighted first-shell EXAFS spectra
(solid green line) and the fit (dashed red line).
Figure S2 (Color online): The fit (dashed red) of a representative pair distance function
of yttrium-doped TiO2 nanoparticles (solid green).
References Cited in the Supplemental Online Material:
[S1] U. Diebold, Surf. Sci. Rep. 48, 53 (2003).
[S2] L. X. Chen et al., J. Phys. Chem. B 101, 10688 (1997).
[S3] M. Matsui and M. Akaogi, Mol. Simul. 6, 239 (1991).
[S4] P. K. Naicker et al., J. Phys. Chem. B 109, 15243 (2005).
[S5] G.V. Lewis and C. R. A. Catlow, J. Phys. C 18, 1149 (1985).