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Metastability of anatase: size dependent and irreversible anatase-rutile phase transition in atomic-level precise titania.

Satoh N, Nakashima T, Yamamoto K - Sci Rep (2013)

Bottom Line: To demonstrate the size dependence in anatase-rutile phase transition of titania, we used quantum-size titania prepared from the restricted number of titanium ions within dendrimer templates for size precision purposes and optical wave guide spectroscopy for the detection.Contrary to some theoretical calculations, the observed irreversibility in the transition indicates the metastablity of anatase; thermodynamics cannot explain the formation of metastable states.The paper will also contribute to the creation of artificial metastable nanostructures with atomic-level precision.

View Article: PubMed Central - PubMed

Affiliation: Photovoltaic Materials Unit, National Institute for Materials Science, Tsukuba, Ibaraki, Japan. SATOH.Norifusa@nims.go.jp

ABSTRACT
Since crystal phase dominantly affects the properties of nanocrystals, phase control is important for the applications. To demonstrate the size dependence in anatase-rutile phase transition of titania, we used quantum-size titania prepared from the restricted number of titanium ions within dendrimer templates for size precision purposes and optical wave guide spectroscopy for the detection. Contrary to some theoretical calculations, the observed irreversibility in the transition indicates the metastablity of anatase; thermodynamics cannot explain the formation of metastable states. Therefore, we take into account the kinetic control polymerization of TiO6 octahedral units to explain how the crystal phase of the crystal-nucleus-size titania is dependent on which coordination sites, cis- or trans-, react in the TiO6 octahedra, suggesting possibilities for the synthetic phase control of nanocrystals. In short, the dendrimer templates give access to crystal nucleation chemistry. The paper will also contribute to the creation of artificial metastable nanostructures with atomic-level precision.

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TEM analysis of 60TiO2.(a) TEM image and (b) the size distribution of 60TiO2. The TEM sample was prepared without annealing at 500°C due to no heat resistant TEM grids.
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f2: TEM analysis of 60TiO2.(a) TEM image and (b) the size distribution of 60TiO2. The TEM sample was prepared without annealing at 500°C due to no heat resistant TEM grids.

Mentions: Figure 2 shows a TEM image of hydrolysed 60TiO2 and Table 1 summarizes the other size characteristic data for 60TiO2. The diameter of the particle observed in TEM is 1.97 ± 0.15 (s.d., n = 100) nm, which agrees with the modelling sizes cleaved from the bulk crystal structures (Supplementary Fig. S3). The AFM images of the hydrolysed and thermorised 60TiO2 reveal that the chemical conversion process does not affect the heights (Supplementary Fig. S4). As observed in 14 and 30TiO2, E(r) estimated from the Tauc plot of OWG spectra depends on the chemical conversion process (Supplementary Fig. S5). The experimental E(r) of hydrolysed and thermorised 60TiO2 corresponds with E(r) calculated using equation (2) for the rutile and anatase parameters, respectively (Supplementary Fig. S6). These results indicate that the TPM-DPA serves as a template for precise size control of size of 60TiO2 and that rutile phase as well as anatase phase forms in nano scale less than 2 nm.


Metastability of anatase: size dependent and irreversible anatase-rutile phase transition in atomic-level precise titania.

Satoh N, Nakashima T, Yamamoto K - Sci Rep (2013)

TEM analysis of 60TiO2.(a) TEM image and (b) the size distribution of 60TiO2. The TEM sample was prepared without annealing at 500°C due to no heat resistant TEM grids.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3675453&req=5

f2: TEM analysis of 60TiO2.(a) TEM image and (b) the size distribution of 60TiO2. The TEM sample was prepared without annealing at 500°C due to no heat resistant TEM grids.
Mentions: Figure 2 shows a TEM image of hydrolysed 60TiO2 and Table 1 summarizes the other size characteristic data for 60TiO2. The diameter of the particle observed in TEM is 1.97 ± 0.15 (s.d., n = 100) nm, which agrees with the modelling sizes cleaved from the bulk crystal structures (Supplementary Fig. S3). The AFM images of the hydrolysed and thermorised 60TiO2 reveal that the chemical conversion process does not affect the heights (Supplementary Fig. S4). As observed in 14 and 30TiO2, E(r) estimated from the Tauc plot of OWG spectra depends on the chemical conversion process (Supplementary Fig. S5). The experimental E(r) of hydrolysed and thermorised 60TiO2 corresponds with E(r) calculated using equation (2) for the rutile and anatase parameters, respectively (Supplementary Fig. S6). These results indicate that the TPM-DPA serves as a template for precise size control of size of 60TiO2 and that rutile phase as well as anatase phase forms in nano scale less than 2 nm.

Bottom Line: To demonstrate the size dependence in anatase-rutile phase transition of titania, we used quantum-size titania prepared from the restricted number of titanium ions within dendrimer templates for size precision purposes and optical wave guide spectroscopy for the detection.Contrary to some theoretical calculations, the observed irreversibility in the transition indicates the metastablity of anatase; thermodynamics cannot explain the formation of metastable states.The paper will also contribute to the creation of artificial metastable nanostructures with atomic-level precision.

View Article: PubMed Central - PubMed

Affiliation: Photovoltaic Materials Unit, National Institute for Materials Science, Tsukuba, Ibaraki, Japan. SATOH.Norifusa@nims.go.jp

ABSTRACT
Since crystal phase dominantly affects the properties of nanocrystals, phase control is important for the applications. To demonstrate the size dependence in anatase-rutile phase transition of titania, we used quantum-size titania prepared from the restricted number of titanium ions within dendrimer templates for size precision purposes and optical wave guide spectroscopy for the detection. Contrary to some theoretical calculations, the observed irreversibility in the transition indicates the metastablity of anatase; thermodynamics cannot explain the formation of metastable states. Therefore, we take into account the kinetic control polymerization of TiO6 octahedral units to explain how the crystal phase of the crystal-nucleus-size titania is dependent on which coordination sites, cis- or trans-, react in the TiO6 octahedra, suggesting possibilities for the synthetic phase control of nanocrystals. In short, the dendrimer templates give access to crystal nucleation chemistry. The paper will also contribute to the creation of artificial metastable nanostructures with atomic-level precision.

Show MeSH
Related in: MedlinePlus