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Nanosized Films of Fe2O3

Hematite Films Intercalated by Lithium

Feb. 28, 2012
Fig. 1: SEM photograph Fe2O3: Li (1%), with magnification of 100.00 K.
Fig. 1: SEM photograph Fe2O3: Li (1%), with magnification of 100.00 K. more
Fig. 1: SEM photograph Fe2O3: Li (1%), with magnification of 100.00 K. Fig. 2: Admittance spectra Fe2O3 thin film measured at room temperature. Fig. 3: SEM photographs Li free Fe2O3 (a), Fe2O3with 1% (c) and Fe2O3with 10% of Li (e), and the ... Table 1: Obtained parameters for different Fe2O3 samples: measurement temperature in degrees of K, ... 

We have investigated nanosized thin films of α-Fe2O3 (hematite) with addition of Lithium, by the impedance spectroscopy (IS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Combining all of these methods, the dependence of structural and electrical properties upon percentage of Li added into the matrix of these metal-oxide films was found.

Introduction

Thin-films containing nanosized grains of Fe2O3 are widely used in research into mainly magnetic and electronic devices [1]. Our intention is to construct charge-discharge Fe2O3-electrode battery with polymer electrolyte and to attach it to solar-cells [2]. Films of iron oxide derived by the chemical deposition method route were investigated by the impedance spectroscopy (IS), SEM, and XRD in order to establish the relation between electrical and the structural properties in nanostructured Fe2O3 and Fe2O3: Li (1% and 10%) films on glass substrate.
IS was applied to measure the resis¬tance of nanostructured Fe2O3 films with different contents of lithium.

By SEM and XRD measurements, we have determined, besides the hematite nature of our samples, that they are composed of the nanosized crystalline grains in the size range from 10 nm to 200 nm. We have also found samples' steadiness during the eight-month period.

Experimental

The samples were nanostructured Fe2O3 films deposited on the glass substrates and were prepared using chemical vapor deposition procedure [3].
The grain size, the crystallinity, and the morphology were observed using scanning field emission electron microscopy (SEM, Zeiss, Supra 35VP). Figure 1 is showing SEM photograph Fe2O3: Li (1%), with magnification of 100.00 K.



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The identification and classification of prepared samples were made by the X-ray diffraction using a D4 Endeavor, Bruker AXS.

Results and Discussion

The primary goal of impedance spectroscopy measurements was to determine the electrical conductivity of the Fe2O3 films and then Fe2O3 films with different contents of Li. Measurements with Zn electrodes were performed in impedance and admittance modes. Figure 2 is showing an example of ac admittance data for the sample of Fe2O3 obtained at room temperature. Resistivities (R) obtained from admittance measurements at room temperature are shown in the second column of table 1.

Scanning field emission electron microscopy and XRD measurements were performed in order to check the grain size, the crystallinity, and the morphology, revealed by other methods [3].

SEM photographs of α-Fe2O3 and of the same material with added Li ions are shown in figure 3. It is clearly visible on lower magnification that sample (a) shows much more homogeneous surface than the samples (c) and (e). The crystallinity is changed and films (c) and (e) became partly and completely amorphous, respectively. The surface of sample (e) shows good homogeneity and on higher magnification some nanoagglomerated grains are visible. Figures 3(b), 3(d), and 3(f) present SEM photographs of the same films after 8 months, demonstrating no significant difference upon earlier results.
The results of the XRD measurements showed the characteristic diffractogram of hematite structure (reference code 01-079-1741, mineral name: Hematite, synthetic, ICSD name: Iron Oxide). XRD clearly shows amorphization of the sample upon addition of Li+ ions [3].

Conclusion

As a conclusion, the present study showed that IS, SEM, and XRD could be applied for grain size and conductivity determination in nanosized films of Fe2O3 and Fe2O3: Li on glass substrate. This particular morphology is suitable for application in an advanced electrochemical cell concept, which could be used as charge storage for solar cells.

Acknowledgments
The authors thank the Croatian and the Slovenian Ministries of Science and Technology for financially supporting this work.

References
[1] Zhang Y. et al.: Chinese Journal of Inorganic Chemistry 20 (9) 1013-1017 (2004)
[2] Turković A. Orel Z.C.: Solar Energy Materials and Solar Cells 45, (3) 275-281 (1997)
[3] Turković A. et al.: Journal of Nanomaterials, Article ID 967307, 8 pages, doi:10.1155/2011/967307 (2011)

Author
Dr. Aleksandra Turković
Institute "Rudjer Bošković"
Department of Materials Physics
Zagreb, Croatia
http://www.irb.hr

 

 

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Keywords: Hematite Films Impedance Spectroscopy (IS) Intercalation of Lithium Nanosized Films of Fe2O3 Scanning Electron Microscopy X-ray Diffraction (XRD)

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