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Ciuparu, Dragoş; Ensuque, Alain; Shafeev, G. A.; Bozon‐Verduraz, François

doi:10.1023/a:1006799701474

Cited by 81 publications

(46 citation statements)

References 14 publications

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“…For precipitated HfO 2 sample with surface area on the order of 200 m 2 /g, crystallization can be delayed by more than 300 °C compared to low surface area hafnia and thick films. The crystallization delay for amorphous nano-zirconia is of similar magnitude [6]. This is consistent with data for HfO 2 nano-particles from PLD deposition studied here.…”

Section: Discussion and Summarysupporting

confidence: 89%

“…1). This is consistent with the results for amorphous zirconia [6,7]. However, in contrast to zirconia, which always crystallizes into the tetragonal modification from the amorphous precursor, hafnia often crystallized directly into the monoclinic phase and only amorphous HfO 2 with high surface area formed the tetragonal phase on crystallization.…”

Section: Crystallization Of Hfo 2 In Bulksupporting

confidence: 90%

“…Amorphous HfO 2 powders were prepared by precipitation from oxychlorides and oxynitrates with hydrazine using a procedure known to produce high-surface area zirconium oxide [6,7]. Aqueous 0.3 mol/l solution of HfO(NO 3 ) 2 (Alfa Aesar 99.9%) or HfOCl 2 was added to hydrazine hydrate N 2 H 4 · H 2 O in a 6 :1 volume ratio.…”

Section: Sample Preparationmentioning

confidence: 99%

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Crystallization in hafnia‐ and zirconia‐based systems

Ushakov

Navrotsky

Yang

et al. 2004

Physica Status Solidi (b)

158

126

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.66. Dk, 68.37.Lp Crystallization of hafnia and zirconia and their alloys with silica and lanthana was studied in bulk and thin film samples by thermal analysis, X-ray diffraction and electron microscopy. Crystallization temperatures of hafnia and zirconia increase by more than 300 °C with increase of surface/interface area of the amorphous phase. Crystallization temperatures of zirconia and hafnia alloys with silica and lanthana increase with dopant content and exceed 900 °C for 50 mol% SiO 2 and LaO 1.5 . Energies for tetragonal HfO 2 and ZrO 2 interfaces with amorphous silica were derived from their crystallization enthalpies from silicates as 0.25 ± 0.08 and 0.13 ± 0.07 J/m 2 , respectively. The crystallization pathways in bulk powders and films of zirconia and hafnia can be interpreted as resulting from thermodynamic stabilization by the surface energy term of tetragonal and amorphous phases over monoclinic.

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Section: Discussion and Summarysupporting

confidence: 89%

Section: Crystallization Of Hfo 2 In Bulksupporting

confidence: 90%

See 1 more Smart Citation

Crystallization in hafnia‐ and zirconia‐based systems

Ushakov

Navrotsky

Yang

et al. 2004

Physica Status Solidi (b)

158

126

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“…It is known that oxygen vacancies are the most common defects in metal oxides. Characteristic absorption bands below the fundamental absorption edge have been occasionally detected in HfO 2 and ZrO 2 and attributed to oxygen vacancies [2,15]. A recent theoretical evaluation of oxygen vacancy species in monoclinic hafnia [3] predicts optical transitions of an electron from valence band to singly ionized vacancy (at 4.67 eV) and doubly ionized vacancy (at 4.91 eV).…”

Section: Discussionmentioning

confidence: 99%

Photoluminescence of sol–gel-prepared hafnia

Kiisk

Lange

Utt

et al. 2010

Physica B: Condensed Matter

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a b s t r a c tWe employed a sol-gel route followed by a thermal treatment (up to 1000 1C) to prepare crystalline (monoclinic) hafnium dioxide. Thorough steady-state and time-resolved photoluminescence characterization of the material within the temperature range of 10-300 K was conducted by using various excitation sources. The most prominent spectroscopic feature of the material was an intense broad emission band centered at 2.3-2.5 eV with an associated excitation band centered at 4.2-4.4 eV (well below the bandgap of monoclinic hafnia). The emission was characterized by an essentially nonexponential, thermally stimulated decay and exposed a marked blue shift with the increase of temperature from 10 to 300 K. Relation of the emission to the intrinsic defects of hafnia is discussed.

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“…Below 400 nm, a strong decrease of the reflectance is observed; the band gap is, according to the not very consistent literature, expected towards shorter wavelengths, i.e. between 250 and 285 nm (30)(31)(32).…”

Section: In Situ Uv-vis Spectroscopymentioning

confidence: 69%

Isomerization of n-butane and of n-pentane in the presence of sulfated zirconia: formation of surface deposits investigated by in situ UV–vis diffuse reflectance spectroscopy

Ahmad

Melsheimer

Jentoft

et al. 2003

Journal of Catalysis

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Catalytic performance and formation of carbonaceous deposits were studied simultaneously during alkane isomerization over sulfated zirconia in a fixed bed flow reactor with an optical window for in situ UV-vis diffuse reflectance spectroscopy. The reactions of n-butane (5 kPa) at 358 and 378 K and of n-pentane (0.25 kPa) at 298 and 308 K passed within 5 h or less through an induction period, a conversion maximum, and a period of deactivation; a steady activity of 41 and 47 µmol g -1 h -1 (isobutane formation) and ≈2.5 µmol g -1 h -1 (isopentane, both temperatures) remained. UV-vis spectra indicate the formation of unsaturated surface deposits; the band positions at 310 nm (n-butane reaction) and 330 nm (npentane) are within the range of monoenic allylic cations. More highly conjugated allylic cations (bands at 370 and 430 nm) became evident during n-butane reaction at 523 K. The chronology of events suggests that the surface deposits are (i) a result only of the bimolecular and not the monomolecular reaction mechanism, and (ii) are formed in a competitive reaction to the alkane products.

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Cited by 81 publications

References 14 publications

Crystallization in hafnia‐ and zirconia‐based systems

Crystallization in hafnia‐ and zirconia‐based systems

Photoluminescence of sol–gel-prepared hafnia

Isomerization of n-butane and of n-pentane in the presence of sulfated zirconia: formation of surface deposits investigated by in situ UV–vis diffuse reflectance spectroscopy

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