Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction
Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO₂ and ZrO₂ synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectrosc...
| Autores: | , , , , , |
|---|---|
| Tipo de recurso: | artículo |
| Fecha de publicación: | 2008 |
| País: | España |
| Institución: | Universidad Complutense de Madrid (UCM) |
| Repositorio: | Docta Complutense |
| Idioma: | inglés |
| OAI Identifier: | oai:docta.ucm.es:20.500.14352/52147 |
| Acceso en línea: | https://hdl.handle.net/20.500.14352/52147 |
| Access Level: | acceso abierto |
| Palabra clave: | 538.9 Ceramic oxide powders Nanocrystalline ZrO₂ Microwave plasma Correlation spectroscopy Quadrupole interactions Zirconia Temperature Pac Particles Complexes Física de materiales Física del estado sólido 2211 Física del Estado Sólido |
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Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffractionForker, M.Presa Muñoz De Toro, Patricia Marcela De LaHoffbauer, W.Schlabach, S.Bruns, M.Szabó, D. V.538.9Ceramic oxide powdersNanocrystalline ZrO₂Microwave plasmaCorrelation spectroscopyQuadrupole interactionsZirconiaTemperaturePacParticlesComplexesFísica de materialesFísica del estado sólido2211 Física del Estado SólidoStructure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO₂ and ZrO₂ synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectroscopy. The PAC technique was used to measure the electric quadrupole interactions (QIs) of the nuclear probes ^(181)Ta and ^(111)Cd in nanocrystalline HfO₂ and ZrO₂ as a function of temperature. For comparison, the QI of ^(181)Ta in the bulk oxides was determined in the same temperature range 300 K ≤ T ≤ 1550 K. The oxygen-metal ratio of the as- ynthesized particles was determined by x-ray photoelectron spectroscopy to be in the range 1.4 ≤ x ≤ 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-ZrO₂, Al₂O₃-coated n-ZrO₂, and Al₂O₃-coated n-HfO₂ are synthesized in the tetragonal or cubic modification with a particle size d < 5 nm, whereas bare n-HfO₂ is mainly monoclinic. The grain growth activation enthalpy of bare n-ZrO₂ is Q_(A)=32(5)kJ/mol. Coating with Al₂O₃ 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 (m) phase up to T ≤ 1400 K. In coated n-ZrO₂ /Al₂O₃, the monoclinic and tetragonal (t) phases coexist over a large temperature range, whereas uncoated, initially tetragonal or cubic (t or c) n-ZrO₂ presents a sharp m↔t transition. A “defect” component involving 30%–40% of the probe nuclei appears in the ^(181)Ta PAC spectra of all nanoparticles when these are cooled from high temperatures T ≥ 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 < 100 nm suggests that mobile electrons are available only in the surface region of the oxide particles, either from oxygen vacancies (Vo) and/or Vo- 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 HfO₂ and ZrO₂. The temperature dependence of the ^(181)Ta defect fraction is consistent with a Ta_(+) impurity level at E_d ~ 0.9 and 0.6 eV below the hafnia and zirconia conduction band, respectively.American Physical SocietyUniversidad Complutense de Madrid20082008-02-0120082008-02-01journal articlehttp://purl.org/coar/resource_type/c_6501info:eu-repo/semantics/articleapplication/pdfhttps://hdl.handle.net/20.500.14352/52147reponame:Docta Complutenseinstname:Universidad Complutense de Madrid (UCM)Inglésengopen accesshttp://purl.org/coar/access_right/c_abf2info:eu-repo/semantics/openAccessoai:docta.ucm.es:20.500.14352/521472026-06-02T12:44:21Z |
| dc.title.none.fl_str_mv |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction |
| title |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction |
| spellingShingle |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction Forker, M. 538.9 Ceramic oxide powders Nanocrystalline ZrO₂ Microwave plasma Correlation spectroscopy Quadrupole interactions Zirconia Temperature Pac Particles Complexes Física de materiales Física del estado sólido 2211 Física del Estado Sólido |
| title_short |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction |
| title_full |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction |
| title_fullStr |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction |
| title_full_unstemmed |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction |
| title_sort |
Structure, phase transformations, and defects of HfO₂ and ZrO₂ nanoparticles studied by ^(181)Ta and ^(111)Cd perturbed angular correlations, ^(1) H magic-angle spinning NMR, XPS, and x-ray and electron diffraction |
| dc.creator.none.fl_str_mv |
Forker, M. Presa Muñoz De Toro, Patricia Marcela De La Hoffbauer, W. Schlabach, S. Bruns, M. Szabó, D. V. |
| author |
Forker, M. |
| author_facet |
Forker, M. Presa Muñoz De Toro, Patricia Marcela De La Hoffbauer, W. Schlabach, S. Bruns, M. Szabó, D. V. |
| author_role |
author |
| author2 |
Presa Muñoz De Toro, Patricia Marcela De La Hoffbauer, W. Schlabach, S. Bruns, M. Szabó, D. V. |
| author2_role |
author author author author author |
| dc.contributor.none.fl_str_mv |
Universidad Complutense de Madrid |
| dc.subject.none.fl_str_mv |
538.9 Ceramic oxide powders Nanocrystalline ZrO₂ Microwave plasma Correlation spectroscopy Quadrupole interactions Zirconia Temperature Pac Particles Complexes Física de materiales Física del estado sólido 2211 Física del Estado Sólido |
| topic |
538.9 Ceramic oxide powders Nanocrystalline ZrO₂ Microwave plasma Correlation spectroscopy Quadrupole interactions Zirconia Temperature Pac Particles Complexes Física de materiales Física del estado sólido 2211 Física del Estado Sólido |
| description |
Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO₂ and ZrO₂ synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectroscopy. The PAC technique was used to measure the electric quadrupole interactions (QIs) of the nuclear probes ^(181)Ta and ^(111)Cd in nanocrystalline HfO₂ and ZrO₂ as a function of temperature. For comparison, the QI of ^(181)Ta in the bulk oxides was determined in the same temperature range 300 K ≤ T ≤ 1550 K. The oxygen-metal ratio of the as- ynthesized particles was determined by x-ray photoelectron spectroscopy to be in the range 1.4 ≤ x ≤ 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-ZrO₂, Al₂O₃-coated n-ZrO₂, and Al₂O₃-coated n-HfO₂ are synthesized in the tetragonal or cubic modification with a particle size d < 5 nm, whereas bare n-HfO₂ is mainly monoclinic. The grain growth activation enthalpy of bare n-ZrO₂ is Q_(A)=32(5)kJ/mol. Coating with Al₂O₃ 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 (m) phase up to T ≤ 1400 K. In coated n-ZrO₂ /Al₂O₃, the monoclinic and tetragonal (t) phases coexist over a large temperature range, whereas uncoated, initially tetragonal or cubic (t or c) n-ZrO₂ presents a sharp m↔t transition. A “defect” component involving 30%–40% of the probe nuclei appears in the ^(181)Ta PAC spectra of all nanoparticles when these are cooled from high temperatures T ≥ 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 < 100 nm suggests that mobile electrons are available only in the surface region of the oxide particles, either from oxygen vacancies (Vo) and/or Vo- 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 HfO₂ and ZrO₂. The temperature dependence of the ^(181)Ta defect fraction is consistent with a Ta_(+) impurity level at E_d ~ 0.9 and 0.6 eV below the hafnia and zirconia conduction band, respectively. |
| publishDate |
2008 |
| dc.date.none.fl_str_mv |
2008 2008-02-01 2008 2008-02-01 |
| dc.type.none.fl_str_mv |
journal article http://purl.org/coar/resource_type/c_6501 |
| dc.type.openaire.fl_str_mv |
info:eu-repo/semantics/article |
| format |
article |
| dc.identifier.none.fl_str_mv |
https://hdl.handle.net/20.500.14352/52147 |
| url |
https://hdl.handle.net/20.500.14352/52147 |
| dc.language.none.fl_str_mv |
Inglés eng |
| language_invalid_str_mv |
Inglés |
| language |
eng |
| dc.rights.none.fl_str_mv |
open access http://purl.org/coar/access_right/c_abf2 |
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info:eu-repo/semantics/openAccess |
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open access http://purl.org/coar/access_right/c_abf2 |
| eu_rights_str_mv |
openAccess |
| dc.format.none.fl_str_mv |
application/pdf |
| dc.publisher.none.fl_str_mv |
American Physical Society |
| publisher.none.fl_str_mv |
American Physical Society |
| dc.source.none.fl_str_mv |
reponame:Docta Complutense instname:Universidad Complutense de Madrid (UCM) |
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Universidad Complutense de Madrid (UCM) |
| reponame_str |
Docta Complutense |
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Docta Complutense |
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|
| repository.mail.fl_str_mv |
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1869404948921319424 |
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15,300719 |