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Figure 22. Room temperature magnetization curve of Fe3 O4 deposited at 450 °C on silicon. Reprinted with permission from [428], S. Mathur et al., Chem. Vap. Deposifion 8, 277 (2002). © 2002, Wiley-VCH.

distribution. TEM images revealed a homogeneous distribution of highly faceted hematite particles (Fig. 24).

Although the magnetic properties of this samples reproduce reported data on a-Fe2O3, for the first time the existence of thermal hysteresis of both structural and magnetic hyperfine parameters at the Morin transition was observed (Fig. 25). The detailed Mossbauer measurements revealed a jump in hyperfine parameters (HPs) at T ~ TM, a distinctive feature of Morin transition observed at 256(2) K [445]. The analysis of HPs as a function of temperature discards the coexistence of low- and high-temperature phases with different crystal symmetries as the possible origins of this hys-teretic behavior.

Nanocrystalline tion because of ous potential

TiO2 has received significant atten-its improved properties and numer-applications, including nanoporous solar

Uncoated

Figure 21. SEM images of iron oxide phases. (a) Hematite. (b) Magnetite.

Figure 23. SEM images of AFM cantilever uncoated (a) and coated with hematite (b and d) and magnetite (c and e). Reprinted with permission from [428], S. Mathur et al., Chem. Vap. Deposifion 8, 277 (2002). © 2002, Wiley-VCH.

Figure 24. HR-TEM micrographs and XRD pattern of the a-Fe2O3 particles.

cells, photochemical applications and optical coatings, etc. [446-448]. The photocatalytically active TiO2 is currently used for so-called self-cleaning coatings in which titanium oxide nanocrystals are deposited as a porous film on the desired substrate. When illuminated, these materials oxidize the organic compounds present in the system, eventually degrading these compounds to water and carbon dioxide.

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