Nanocrystalline GdFeO 3 via the gel-combustion process
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Nanocrystalline GdFeO3 powder was synthesized by a combustion technique, using glycine as the fuel and the corresponding metal nitrates as oxidants. Five different molar ratios of fuel-to-oxidant were chosen to study the effect of fuel content on the phase formation and the powder properties. The powders after calcination were characterized by x-ray diffraction (XRD) and crystallite sizes calculated by x-ray line broadening. The crystallite sizes for the phase pure products after calcination at 600 °C were in the range 40–65 nm. The transmission electron microscopy observations clearly highlight the pronounced crystallinity for the propellant chemistry samples. The nature of the agglomerates was investigated by light scattering studies. The lattice thermal expansion behavior was also studied by high-temperature XRD.
I. INTRODUCTION
The synthesis and study of nanocrystalline materials has gained tremendous momentum recently. The nanocrystalline ceramics have far superior powder properties such as large surface area, higher chemical reactivity, and better sinterability etc. Another motivation for preparing the nanocrystalline materials is to tune the various properties, which usually show a gradual transition from solid-state matter to molecular structures as the particle size is decreased. Such materials usually show greatly modified electro-optical1,2 and catalytic3 properties compared to their microcrystalline counterparts. Even the sintering rates are considerably enhanced and the sintering temperatures are lowered with sinteractive nanocrystalline powders as the starting materials.4,5 GdFeO3 belongs to the perovskite rare-earth orthoferrites. These materials form an important class with a wide range of applications. These ferrite materials are used as catalysts,6 ferroelectrics, and semiconductors, and others are used as magnetic and magneto-optical materials.7 In general, the orthoferrites are antiferromagnetic due to the antiparallel alignment of the magnetic moments of the Fe sublattices. Various solution techniques are capable of preparing mixed oxides in the nanocrystalline form. However, in these processes, one has to maintain precise control on the positions of the metal atoms in the precursors to have the desired products. In the absence of a precise control over precursors, various intermediate species are formed apart from the desired composition. Thus, during the synthesis of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0337 2654
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 10, Oct 2005 Downloaded: 11 Nov 2014
LnFeO 3 oxides, undesired phases coexist 8,9 (i.e., Ln3Fe5O12 and Fe3O4) as the garnet phase (Ln5Fe3O12) is thermodynamically more stable than LnFeO 3 .10 Lately, preparation of these materials have received tremendous renewed interest.8–10 In this paper, we report for the first time the synthesis of single phasic nanocrystalline GdFeO3, free from the garnet phase by the gel combustion technique using glycine as the fu
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