ESR Characterization of ZrO2 Nanopowder

Liu, Huiwen; Feng, Liang; Zhang, Xushou; Xue, Qianzhong

doi:10.1021/j100001a050

Cited by 148 publications

(113 citation statements)

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“…In spite of some systematic uncertainty due to line broadening by localized electrostatic charge buildup of the nonconducting samples, this indicates a sizable concentration of oxygen vacancies in the surface region of the nanoparticles, in agreement with the pronounced decrease ͑relative to the bulk material͒ of the cation-oxygen coordination seen in the extended x-ray absorption fine structure ͑EXAFS͒ spectra of nanocrystalline zirconia. 19,20 A similar oxygen-metal ratio x ϳ 1.7 has been reported by Liu et al 21 for zirconia nanoparticles prepared by precipitation methods.…”

Section: A Synthesissupporting

confidence: 78%

“…A particle size effect has also been reported in an electron spin resonance study of ZrO 2 nanopowders by Liu et al 21 These authors have detected a surface-related paramagnetic F-center signal which they attribute to the trapping of elec Ta in bare and coated nanoparticles of HfO 2 and coarse-grained HfO 2 ͑from top͒ as a function of temperature. Data for nano-oxide powders and pellets are shown.…”

supporting

confidence: 54%

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Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

et al. 2008

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Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO 2 and ZrO 2 synthesized in a microwave-plasma process have been investigated by x-ray diffraction ͑XRD͒, transmission electron microscopy ͑TEM͒, and perturbed angular correlation ͑PAC͒ spectroscopy. The PAC technique was used to measure the electric quadrupole interactions ͑QIs͒ of the nuclear probes Ta in the bulk oxides was determined in the same temperature range 300 K ഛ T ഛ 1550 K. The oxygen-metal ratio of the as-synthesized particles was determined by x-ray photoelectron spectroscopy to be in the range 1.4ഛ x ഛ 1.8. A hydrate surface layer with a hydrogen content of 5 -10 wt %, consisting of chemisorbed hydroxyl groups and organic precursor fragments, was detected by 1 H magic-angle spinning NMR. XRD and TEM show that bare n-ZrO 2 , Al 2 O 3 -coated n-ZrO 2 , and Al 2 O 3 -coated n-HfO 2 are synthesized in the tetragonal or cubic modification with a particle size d Ͻ 5 nm, whereas bare n-HfO 2 is mainly monoclinic. The grain growth activation enthalpy of bare n-ZrO 2 is Q A =32͑5͒ kJ/ mol. Coating with Al 2 O 3 stabilizes the tetragonal over the monoclinic phase, both in hafnia and zirconia nanoparticles. While TEM micrographs of the native nanoparticles reveal a well-ordered cation sublattice, the observation of a broad QI distribution in the PAC spectra suggests a high degree of disorder of the oxygen sublattice. The gradual transformation of the disordered state and the phase evolution were studied by high-temperature QI measurements. Hafnia nanoparticles persist in the monoclinic ͑m͒ phase up to T ഛ 1400 K. In coated n-ZrO 2 / Al 2 O 3 , the monoclinic and tetragonal ͑t͒ phases coexist over a large temperature range, whereas uncoated, initially tetragonal or cubic ͑t or c͒ n-ZrO 2 presents a sharp m ↔ t transition. A "defect" component involving 30%-40% of the probe nuclei appears in the 181Ta PAC spectra of all nanoparticles when these are cooled from high temperatures T ജ 1200 K. The temperature dependence of this component can be reproduced by assuming that Ta impurities in hafnia and zirconia may trap electrons at low temperatures. The observation that the defect component appears only in nanoparticles with diameter d Ͻ 100 nm suggests that mobile electrons are available only in the surface region of the oxide particles, either from oxygen vacancies ͑V O ͒ and/or V O -hydrogen donors at the interface of the nanoparticles and their hydrate layers. This conclusion is supported by the absence of a size effect for 111 Cd probes in HfO 2 and ZrO 2 . The temperature dependence of the 181 Ta defect fraction is consistent with a Ta + impurity level at E d ϳ 0.9 and 0.6 eV below the hafnia and zirconia conduction band, respectively.

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Section: A Synthesissupporting

confidence: 78%

supporting

confidence: 54%

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

et al. 2008

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“…Zirconia [26] was prepared using an aqueous solution of zirconyl chloride with the dropwise addition of NH 4 OH for 4 hours (pH 10) with continuous stirring. The precipitate was washed with triply distilled water using a Soxhlet's apparatus for 24 h. The Cl -test with AgNO 3 was found to be negative.…”

Section: Catalyst Preparationmentioning

confidence: 99%

Liquid‐Phase Aerobic Oxidation of Benzyl Alcohol Catalyzed by Pt/ZrO₂

Ilyas

Sadiq

2007

Chem Eng & Technol

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The oxidation of benzyl alcohol by molecular oxygen in the liquid phase and catalyzed by Pt/ZrO2 using n-heptane as the solvent was studied. Pt/ZrO 2 was very active and 100 % selective for benzyl alcohol conversion to benzaldehyde. The catalyst can be separated by filtration and reused. No leaching of Pt or Zr into the solution was observed. Typical batch reactor kinetic data were obtained and fitted to the Langmuir-Hinshelwood, Eley-Rideal and Mars-van Krevelen models of heterogeneously catalyzed reactions. The Langmuir-Hinshelwood model was found to give a better fit. The rate-determining step was proposed to involve direct interaction of an adsorbed oxidizing species with the adsorbed reactant or an intermediate product of the reactant. H 2 O 2 was also proposed to be an intermediate product.n-Heptane was found to be an appropriate solvent in this reaction system.

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“…The spectra were collected on stations at the CCLRC Daresbury Synchrotron Radiation Source (SRS) using procedures described in earlier work [23,36,37,50,58,59,72,73].…”

Section: Microstructure Of Nanoionicsmentioning

confidence: 99%

“…It has also been the subject of numerous investigations as a nanoionic material due to the apparent ease of preparation. We use the term 'apparent' as the most common procedure of heating the hydroxide at modest temperature (500°C) for a short period (60 min) has been reported as a means of producing 10 nm particle sizes of the oxide [72]. Later work [36] has shown this procedure does not produce the pure oxide but material that contains a considerable fraction of hydroxyl species, sufficient to invalidate any EXAFS studies.…”

Section: Zirconiamentioning

confidence: 99%

Structure and dynamics in nanoionic materials

Chadwick

Savin

2006

Solid State Ionics

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Nanomaterials, materials with particle dimensions less than 100 nm, show a range of unusual properties when compared with their bulk counterparts. Atomic transport is one of these properties and nanomaterials have been reported as having exceptionally high diffusion coefficients. In the case of ionic materials the atomic transport is important in a number of technological applications where they are used as solid electrolytes, for example in sensors, batteries and fuel cells. Hence ionic nanomaterials often referred to as nanoionics, can offer the means of producing electrolytes with improved performance. This contribution will examine the mechanisms of atomic transport in nanoionics in two model materials, zirconia and lithium niobate. Since an understanding of these mechanisms is dependent on knowledge of the microstructure of the materials consideration will also be given to the structural characterisation of the materials, with a focus on X-ray absorption spectroscopy. The use of this technique to characterise mesoporous a-Fe 2 O 3 is also discussed.

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ESR Characterization of ZrO2 Nanopowder

Cited by 148 publications

References 2 publications

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

Liquid‐Phase Aerobic Oxidation of Benzyl Alcohol Catalyzed by Pt/ZrO₂

Structure and dynamics in nanoionic materials

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ESR Characterization of ZrO2 Nanopowder

Cited by 148 publications

References 2 publications

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

Liquid‐Phase Aerobic Oxidation of Benzyl Alcohol Catalyzed by Pt/ZrO2

Structure and dynamics in nanoionic materials

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Liquid‐Phase Aerobic Oxidation of Benzyl Alcohol Catalyzed by Pt/ZrO₂