Neutron Diffraction Study of the Size-Induced Tetragonal to Monoclinic Phase Transition in Zirconia Nanocrystals

Baldinozzi, Gianguido; Siméone, David; Gosset, Dominique; Dutheil, M.

doi:10.1103/physrevlett.90.216103

Cited by 106 publications

(63 citation statements)

References 21 publications

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“…Kirsch et al 38 have found Q A =33͑8͒ kJ/ mol for n-ZrO 2 colloids. In a neutron diffraction study of n-ZrO 2 produced by freeze-drying, Baldinozzi et al 39 arrived at Q A Ϸ 40 kJ/ mol. The data of Wür-schum et al 40 ͑open circles in Fig.…”

Section: Grain Growth Of Nanocrystalline Zro 2 and Hfomentioning

confidence: 99%

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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: Grain Growth Of Nanocrystalline Zro 2 and Hfomentioning

confidence: 99%

“…39 Hf. For the production of the PAC sources, a few milligrams of nanoparticles of HfO 2 and ZrO 2 ͑doped with a Hf concentration of ϳ4 at.…”

Section: Grain Growth Of Nanocrystalline Zro 2 and Hfomentioning

confidence: 99%

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

et al. 2008

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“…To further complicate the issue, the phase stability is a function of size for particles < ca. 100 nm [44], and possibly of particle shape [45]. The transition temperature is pushed to lower temperatures as the size is decreased, so that the tetragonal phase is stable at room temperature for very small particles.…”

Section: Interfacial Chemistrymentioning

confidence: 99%

Theory and modeling of active brazing.

Swol¹,

Miller²,

Lechman³

et al. 2013

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Active brazes have been used for many years to produce bonds between metal and ceramic objects. By including a relatively small of a reactive additive to the braze one seeks to improve the wetting and spreading behavior of the braze. The additive modifies the substrate, either by a chemical surface reaction or possibly by alloying. By its nature, the joining process with active brazes is a complex nonequilibrium non-steady state process that couples chemical reaction, reactant and product diffusion to the rheology and wetting behavior of the braze. Most of the these subprocesses are taking place in the interfacial region, most are difficult to access by experiment. To improve the control over the brazing process, one requires a better understanding of the melting of the active braze, rate of the chemical reaction, reactant and product diffusion rates, nonequilibrium 3 composition-dependent surface tension as well as the viscosity. This report identifies ways in which modeling and theory can assist in improving our understanding. 4 AcknowledgmentThanks to Allen Roach and Carlton Brooks for stimulating discussions of active brazes and surface tensions of metals. The ASC-PEM project is gratefully acknowledged for providing funding. 5This page intentionally left blank.

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“…After annealing up to 870 °C, Paper I, the tetragonal ZrO2 phase was the only observed crystalline phase of ZrO2 at room temperature. This is possibly due to the small grain size in the coating < 30 nm, as the tetragonal phase has a lower surface energy than the monoclinic one, and is thus stabilized even at room temperature [70,71]. See Paper I for further details on the study.…”

Section: Pseudo-binary and -Ternary Oxidesmentioning

confidence: 99%

Thin Film and Plasma Characterization of PVD Oxides

Landälv¹

2017

Linköping Studies in Science and Technology. Dissertations

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The state-of-the-art tools for machining metals are primarily based on a metal-ceramic composite (WC-Co) coated with different combinations of carbide, nitride and oxide coatings. Combinations of these coating materials are optimized to withstand specific wear conditions. Oxide coatings are especially desired because of their possible high hot hardness, chemical inertness with respect to the workpiece, and their low friction.This thesis deals with process and coating characterization of new oxide coatings deposited by physical vapor deposition (PVD) techniques, focusing on the Cr-Zr-O and Al-Cr-Si-O systems.The thermal stability of α-Cr0.28Zr0.10O0.61 deposited by reactive radio frequency (RF)-magnetron sputtering at 500 °C was investigated after annealing up to 870 °C. The annealed samples showed transformation of α-(Cr,Zr)2O3 and amorphous ZrOx-rich areas into tetragonal ZrO2 and bcc Cr. The instability of the α-(Cr,Zr)2O3 is surprising and possibly related to the annealing being done under vacuum, facilitating the loss of oxygen. The stabilization of the room temperature metastable tetragonal ZrO2 phase, due to surface energy effects, may prove to be useful for metal cutting applications. The observed phase segregation of α-(Cr,Zr)2O3 and formation of tetragonal ZrO2 with corresponding increase in hardness for this pseudo-binary oxide system also opens up design routes for pseudo-binary oxides with tunable microstructural and mechanical properties.The inherent difficulties of depositing insulating oxide films with PVD, demanding a closed circuit, makes the investigation of process stability an important part of this research. In this context, we investigated the influence of adding small amount of Si in Al-Cr cathode on plasma characteristics, process parameters, and coating properties. Si was chosen here due to a previous study showing improved erosion behavior of Al-Cr-Si over pure Al-Cr cathode without Si incorporation in the coating.This work shows small improvements in cathode erosion and process stability (lower pressure and cathode voltage) when introducing 5 at % Si in the Al70Cr30-cathode. This also led to fewer droplets at low cathode current and intermediate O2 flow. A larger positive effect on cathode erosion was observed with respect to cleaning the cathode from oxide contamination by increasing cathode current with 50%. However, higher cathode current also resulted in increased amount of droplets in the coating which is undesirable. Through plasma analysis the presence of volatile SiO species could be confirmed but the loss of Si through volatile SiO species was negligible, since the coating composition matched the cathode composition. The positive effect of added Si on the process stability at the cathode surface should be weighed against Si incorporation in the coating. This incorporation may or may not be beneficial for the final application since literature states that Si promotes the metastable γ-phase over the thermodynamically stable α-phase of pure Al2O3, contrary to the effect o...

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Neutron Diffraction Study of the Size-Induced Tetragonal to Monoclinic Phase Transition in Zirconia Nanocrystals

Cited by 106 publications

References 21 publications

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

Structure, phase transformations, and defects ofHfO2andZrO2nanoparticle

Theory and modeling of active brazing.

Thin Film and Plasma Characterization of PVD Oxides

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