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β-Fe2O3 is the scarce polymorph of Fe2O3 phases and is transformed easily into α-Fe2O3 at high temperature. However, its crystal structure and the transformation mechanism to α-Fe2O3 are still unclear because of the difficulty in obtaining monophasic β-Fe2O3 crystals. We established a synthesis method of the monophasic β-Fe2O3. It was synthesized by a two-step reaction: heating a mixture of Na2SO4 and Fe2(SO4)3 in air at 250 °C to form NaFe(SO4)2, and subsequent heating the resultant phase with NaCl in air at 500 °C. The crystal structure was refined to a bixbyite-type cubic structure (Ia3̅) with a = 9.4039(1) Å by the Rietveld method. Single crystalline β-Fe2O3 particles of approximately 1 μm in size were topotactically transformed into single α-Fe2O3 crystals. Electron diffraction analysis revealed the crystallographic orientation relationships between β-Fe2O3 and α-Fe2O3 to be [100]β//[0001]α, [010]β//[101̅0]α, and [001]β//[1̅21̅0]α.

Inspired by the traditional Japanese pigment Fukiya bengala, nanocomposite materials were synthesized using a polymer complex method, comprising Al-substituted α-Fe2O3 (hematite) particles with diameters ranging from 40 to 100 nm and ultrafine Fe-substituted α-Al2O3 (corundum) particles smaller than 10 nm in diameter. The obtained powders exhibited a vivid yellowish-red color and high thermostability, making them attractive as potential overglaze enamels on porcelain. Quantitative color measurements revealed that, when heated to 700, 800, and 900 °C, samples displayed high lightness (L*) and color-opponent dimensions (a* and b*) at 10 mol % Al. For the same particle size samples, L*, a*, and b* values increased with the Al molar ratio, revealing that Al substitution in the hematite structure intrinsically enhances lightness and chroma in hematite color. These samples mostly retained their color upon reheating at 900 °C, indicating their high thermostability. This thermostability should originate from the Al substitution-induced enhancement in lightness and chroma in hematite color, which should counter color fading caused by particle growth. These composite materials are expected to find application in the porcelain industry, cosmetics, and nanotechnology.

The biogenous iron oxide (BIO) from Leptothrix ochracea was transformed to an organic-inorganic hybrid support to prepare an excellent immobilized enzyme showing high catalytic performance.

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The effect of Co 2+ ion on the magnetic properties of the sol-gel derived cobalt ferrite thin films (400 nm thickness) was studied. Films with different solution composition ([Co 2+ ]/[Fe 3+ ] = 0.5-1.0) were deposited on a Si substrate from the precursor containing an aqueous solution of FeCl 3 ?6H 2 O and CoCl 2 ?6H 2 O. Deposited films were heat treated at different temperatures (700-1100 uC) and were characterized by X-ray diffraction using Cu Ka radiation. The films containing a nonstoichiometric a-(Fe 12x Co x ) 2 O 3 phase were obtained in addition to a small amount of CoO at relatively lower temperatures. With increasing heat treatment temperature, nonstoichiometric a-(Fe 12x Co x ) 2 O 3 was decomposed to stoichiometric a-Fe 2 O 3 and the CoFe 2 O 4 phase was intensified. Only the films obtained from the solution enriched with Co showed the single phase of CoFe 2 O 4 , though the Co to Fe content ratio analyzed by inductive coupled plasma spectroscopy (ICP) and energy dispersive X-ray spectroscopy (EDX) was nearly consistent with that of the starting solutions. The study of surface morphology of the films by using field emission scanning electron microscope (FESEM) showed that films were homogeneously distributed throughout the surface of the substrate and the grain sizes were in the range of 60 to 140 nm. Magnetic properties of the films, including the Curie temperature, were studied by using a vibrating sample magnetometer (VSM) and conversion electron Mo ¨ssbauer spectroscopy (CEMS). The Curie temperature and the magnetic hyperfine fields of the films slightly decreased with increasing molar ratio of the Co 2+ and Fe 3+ ions while the saturation magnetization reached a maximum value with the film composition of x = 0.28.

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