Thermal evolution of the microstructure of nanosized LaFeO 3 powders from the thermal decomposition of a heteronuclear c
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Thermal evolution of the microstructure of nanosized LaFeO3 powders from the thermal decomposition of a heteronuclear complex, La[Fe(CN)6 ] ? 5H2 O Enrico Traversa and Patrizia Nunziante Dipartimento di Scienze e Tecnologie Chimiche, Universita’ di Roma “Tor Vergata”, Via della Ricerca Scientifica, 00133 Roma, Italy
Masatomi Sakamoto Department of Materials and Biological Chemistry, Faculty of Science, Yamagata University, Yamagata 990, Japan
Yoshihiko Sadaoka Department of Materials Science and Engineering, Faculty of Engineering, Ehime University, Matsuyama 790-77, Japan
Maria Cristina Carotta and Giuliano Martinelli INFM, Dipartimento di Fisica, Universita’ di Ferrara, Via Paradiso 12, 44100 Ferrara, Italy (Received 16 September 1996; accepted 17 July 1997)
The thermal decomposition of a heteronuclear complex, La[Fe(CN)6 ] ? 5H2 O, leads to the preparation of nanosized single-phase perovskite-type LaFeO3 powders. The microstructural evolution of LaFeO3 with the temperature has been studied by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The product of the decomposition at 500 ±C consists of nanoporous grains which have the morphology of the complex, but diffracting as a monocrystal of LaFeO3 . At the higher temperatures, the nanosized particles start to separate from each other, still keeping the shape of the complex grains and forming soft agglomerates. The formation of LaFeO3 from the complex at low temperatures is facilitated by the formation of an orthorhombic transition phase. I. INTRODUCTION
LaFeO3 is a mixed conducting oxide with a distorted perovskite-type crystal structure. This oxide is typically p-type semiconductor, in which substitution of cations with lower valence produces additional mobile anion vacancies.1,2 LaFeO3 can have highly nonstoichiometric composition, which may lead to n-type electronic conduction when the oxygen content is substoichiometric. These interesting functional properties make LaFeO3 particularly suitable for applications as a material for sensors, for the detection of vapors and gases such as humidity, alcohol, oxygen, hydrocarbons, CO, and NO2 .3–13 For these applications, the achievement of controlled porous structures is essential. The control of the microstructure in the final products can be obtained using ultrafine, homogeneously sized ceramic powders as starting materials. The conventional method for the preparation of heterometallic oxides, such as LaFeO3 perovskite-type oxide, is the solid-state reaction at high temperatures of the corresponding single oxides (La2 O3 and Fe2 O3 , in this case). By using this method, it is difficult to obtain single phase materials, since residual amounts of the starting oxides are likely to remain in the final product, unless repeated cycles of milling and heating J. Mater. Res., Vol. 13, No. 5, May 1998
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