Surface Segregation in SnO2–Fe2O3 Nanopowders and Effects in Mössbauer Spectroscopy

Castro, Ricardo H. R.; Hidalgo, Pilar; Coaquira, J. A. H.; Bettini, Jefferson; Zanchet, Daniela; Gouvêa, Douglas

doi:10.1002/ejic.200400879

Cited by 54 publications

(32 citation statements)

References 24 publications

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“…Undoped and Ni-doped SnO 2 nanoparticles have been synthesized using the polymer precursor method (Pechini's method [10]). Tin citrate (Sn 2 -(C 6 O 7 H 4 )·H 2 O), obtained from SnCl 2 ·2H 2 O and citric acid precursors, and Ni(NO 3 ) 2 6H 2 O were used to produce the nanoparticles.…”

Section: Methodsmentioning

confidence: 99%

Experimental study of the structural, microscopy and magnetic properties of Ni-doped SnO2 nanoparticles

Aragón

Coaquira

Hidalgo

et al. 2010

Journal of Non-Crystalline Solids

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A polymer precursor method has been used to synthesize Ni-doped SnO 2 nanoparticles. X-ray diffraction (XRD) data analyses indicate the exclusive formation of nanosized particles with rutile-type phase (tetragonal SnO 2 ) for Ni contents below 10 mol%. In this concentration range, the particle sizes decrease with increasing Ni content and a bulk solid solution limit was determined at~1 mol%. Ni surface enrichment is present at concentrations higher than the solution limit. Only above 10 mol% Ni, the formation of a second NiO-related phase has been determined. Magnetization measurements suggest the occurrence of ferromagnetism for samples in the solid solution regime (below~1 mol%). This ferromagnetism is associated with the exchange interaction between electron spins trapped on oxygen vacancies, and is enhanced as the amount of Ni 2+ substituting at Sn 4+ sites increases. Above the solid solution limit, ferromagnetism is destroyed by the Ni surface enrichment and the system behaves as a paramagnet.

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Section: Methodsmentioning

confidence: 99%

Experimental study of the structural, microscopy and magnetic properties of Ni-doped SnO2 nanoparticles

Aragón

Coaquira

Hidalgo

et al. 2010

Journal of Non-Crystalline Solids

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“…When higher amounts of Co 3 O 4 (5 mol%) [10] or CoO (2 mol%) [27] are added to SnO 2 in mixed oxide procedures, the diffraction peaks of Co 2 SnO 4 are visible without the need of magnification of the XRD patterns. On the other hand, it has been reported that there is a low probability for iron to extensively form a solid solution with tin oxide because of the different crystalline structure between SnO 2 and Fe 2 O 3 [28]. Nevertheless, the high density of sample SFN and results from previous works [9,13] prove that a certain degree of solid solution formation of Fe in SnO 2 indeed takes place.…”

Section: Microstructural Properties Of Sintered Samplesmentioning

confidence: 86%

From tin oxalate to (Fe, Co, Nb)-doped SnO2: Sintering behavior, microstructural and electrical features

Parra

Ramajo

Góes

et al. 2008

Materials Research Bulletin

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Highly reactive SnO 2 -doped nanocrystalline powders with average particle size of 20 nm and specific surface areas above 30 m 2 / g were obtained through the polymeric precursor method with tin oxalate (SnC 2 O 4 ) as a chloride-free precursor for SnO 2 . Powders and sintered discs were characterized by means of X-ray powder diffraction (XRD), SEM and TEM. The influence of Co and Fe on the microstructure development and on the electrical properties of dense SnO 2 -based ceramics was studied. Co and Fe species were found to decrease in more than 70 8C the sintering temperature of SnO 2 with respect to mixed oxide procedures. Secondary phases enriched in Co and Fe were detected and identified in sintered samples with XRD. Current-voltage curves were registered for electrical characterization. Doping with iron increased the electrical breakdown field and a nonlinearity coefficient of 20 was achieved. #

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“…A validade deste modelo nesta situação é reforçada através das análises de microscopia eletrônica disponíveis na literatura para pós produzidos pelo mesmo método de síntese e mesmas concentrações [31,32]. Observase das micrografias que as partículas são relativamente isotrópicas, reforçando a hipótese do uso da Equação (A) para o cálculo das energias.…”

Section: Energia De Superfície Do Sno 2 Dopadounclassified

“…Nota-se que a presença dos aditivos diminui a energia de superfície dos materiais dopados em relação ao SnO 2 puro. Isso é consistente com as observações da literatura relativas à segregação dos aditivos na superfície do SnO 2 [4,17,31,32]. Essa segregação leva à redução em σ conforme a Equação B.…”

Section: Energia De Superfície Do Sno 2 Dopadounclassified

Determinação das energias de superfície do SnO2 puro e dopado

Castro

Hidalgo²,

Gouvêa³

et al. 2009

Cerâmica

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INTRODUÇÃOO desenvolvimento de novos nanomateriais é fortemente dependente do controle da estabilização destas nanoestruturas. Quando considerando sínteses bottomtop, podem ser definidos dois métodos básicos de controle das nanoestruturas para gerar estabilização e indução de formatos e tamanhos desejados: o método termodinâmico e o cinético [1]. Particularmente centrando na síntese via líquida de nanopartículas, a aproximação termodinâmica considera que na nucleação existe um raio crítico mínimo relacionado com um balanço entre a energia de volume e a energia de superfície. Como fortemente dependente da energia de superfície, a modulação desta energia é indicada como uma forma natural de controle do tamanho mínimo das nanopartículas [1,2]. No entanto, após a nucleação, o fenômeno de crescimento ocorre espontaneamente, desde que existe uma barreira de energia para nuclear uma nova nanopartícula que, em geral, é maior que aquela para crescer a nanopartícula já nucleada. Para controlar este crescimento, adotam-se soluções usualmente cinéticas. No entanto, observando os modelos de crescimento de nanopartícula por síntese em fase líquida, verifica-se que a energia de superfície tem influência direta também no crescimento do tamanho da partícula em conjunto com o coeficiente de difusão. Isto é, para um processo controlado por difusão, o tamanho médio Mg, Fe, Cr, and Ni.

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Surface Segregation in SnO₂–Fe₂O₃ Nanopowders and Effects in Mössbauer Spectroscopy

Cited by 54 publications

References 24 publications

Experimental study of the structural, microscopy and magnetic properties of Ni-doped SnO2 nanoparticles

Experimental study of the structural, microscopy and magnetic properties of Ni-doped SnO2 nanoparticles

From tin oxalate to (Fe, Co, Nb)-doped SnO2: Sintering behavior, microstructural and electrical features

Determinação das energias de superfície do SnO2 puro e dopado

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