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Beltrán, J. I.; Gallego, S.; Cerdá, Jorge I.; Moya, José S.; Muñoz, M. C.

doi:10.1103/physrevb.68.075401

Cited by 74 publications

(53 citation statements)

References 24 publications

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“…It is possible that not only the atomic and electronic structures but also the interfacial energy is different between Ni/ZrO 2 (001) and Ni/ZrO 2 (111) interfaces. According to recent theoretical studies, there are differences in the interfacial energies, which gives the actual stability of the each interface, between Ni(001)/ZrO 2 (001) 9) and Ni(111)/ZrO 2 (111) 5) interfaces, although the interface plane of Ni is different from each other. Furthermore, Beltrán et al reported that both the Zr-terminated and the Oterminated interfaces are energetically favorable in the Ni(001)/ZrO 2 (001) interface, 9) while Christensen and Carter reported that the O-terminated interface is energetically favorable in the Ni(111)/ZrO 2 (111) interface, 5) which is consistent with our result.…”

Section: Electronic Structurementioning

confidence: 99%

“…6,7) On the other hand, Beltrán et al reported that both the Zr-terminated and Oterminated interfaces are energetically favorable in the Ni(001)/ZrO 2 (001) interface. 8,9) In addition to the theoretical studies, several experimental studies have been carried out. Dickey et al studied the Ni/ZrO 2 interfaces, using Z-contrast imaging technique and EELS analysis, which were fabricated by reduction of the eutectic bonded NiO/ZrO 2 interface, and pointed out that the metallic bonding between Ni and Zr, which may be formed under the reduced atmosphere, is responsible for the stability of the Ni(111)/ZrO 2 (001) interface.…”

Section: Introductionmentioning

confidence: 99%

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Atomic and Electronic Structures of Ni/YSZ(111) Interface

et al. 2004

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Thin Ni films were deposited on the (111) surface of YSZ at 1073 K by a pulsed laser deposition technique. The interfacial atomic structure of Ni/YSZ was investigated by high-resolution transmission electron microscopy (HRTEM). It was found that Ni was epitaxially oriented to the YSZ surface, and the following orientation relationship (OR) was observed: ð111Þ Ni k ð111Þ YSZ , ½1 1 10 Ni k ½1 1 10 YSZ . Geometrical coherency of the Ni/YSZ system was also evaluated by the coincidence of reciprocal lattice points (CRLP) method. It was found that the most coherent OR predicted by CRLP method was ð705Þ Ni k ð111Þ YSZ , ½0 1 10 Ni k ½1 1 10 YSZ , which was not consistent with the experimentally observed OR. To understand the detailed atomic structure, HRTEM image simulations were performed. However, simulated images based on both O-terminated and Zr-terminated interface models were quite similar to the experimental image, and thus it was hard to determine which model is comparable with the actual interface only by the HRTEM image simulations. In order to clarify the termination layer at the interface, electronic structures of the Ni/YSZ interface were investigated by electron energy-loss spectroscopy. It was found that significant differences were observed in O-K edge spectra between the interface and the YSZ crystal interior, and the spectrum from the interface showed similar features to the reference spectrum of bulk NiO. This indicates that the Ni-O interaction occurs at the interface to terminate the oxygen {111} plane of YSZ at the Ni/YSZ interface. In addition, the density of Ni-O bonds across the interface in the experimental OR was larger than that in the most coherent OR predicted by CRLP method, which also suggests that the on-top Ni-O bonds stabilize the Ni/YSZ(111) interface.

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Section: Electronic Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Atomic and Electronic Structures of Ni/YSZ(111) Interface

et al. 2004

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“…We use the SIESTA package [17] with basis sets formed by double-zeta polarized localized numerical atomic orbitals. More details about the conditions of the calculations can be found elsewhere [18]. …”

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confidence: 99%

Magnetism and half-metallicity at the O surfaces of ceramic oxides

Gallego

Beltrán

Cerdá

et al. 2005

J. Phys.: Condens. Matter

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The occurence of spin-polarization at ZrO2, Al2O3 and MgO surfaces is proved by means of abinitio calculations within the density functional theory. Large spin moments, as high as 1.56 µB, develop at O-ended polar terminations, transforming the non-magnetic insulator into a half-metal. The magnetic moments mainly reside in the surface oxygen atoms and their origin is related to the existence of 2p holes of well-defined spin polarization at the valence band of the ionic oxide. The direct relation between magnetization and local loss of donor charge makes possible to extend the magnetization mechanism beyond surface properties.PACS numbers: 75.70. Rf, 73.20.At, When dimensions are reduced to the nanoscale, we are faced to a new understanding of the physical properties of matter: bulk insulators and semiconductors exhibit metallic surfaces [1], non-magnetic materials get spin polarization when forming nanoparticles [2], unstable bulk structures exist in ultrathin film form [3,4], etc. At the origin of these phenomena are the reduced dimensionality and the enhanced role of the surfaces or boundaries in the final properties of the system. Together with its inherent fundamental interest, this has important technological consequences, auspicating the birth of new technologies [5,6]. Special attention is devoted to magnetic low dimensional structures, in particular as sources of spin current in the emerging field of spintronics [5].In this letter, we report on the existence of large magnetic moments and half-metallicity at the O-rich surfaces of ceramic oxides, focusing on ZrO 2 , Al 2 O 3 and MgO. These are non-magnetic ionic insulators widely applied in bulk and thick film form, that have also been grown as ultrathin films and nanometric grains [7]. Their electronic structure can be roughly described as a valence band formed by the filled O 2p orbitals and a conduction band formed by the empty metal levels. When a M x O y unit -M being the metal donor and x,y accounting for the particular metal to oxygen ratio-is broken to form the surface, the loss of coordination of the surface O atoms originates 2p holes in the valence band of the oxide. Our results show that this generates high spin moments at the topmost O layer, which induce magnetization at the adjacent planes and, remarkably, alter the electronic structure of the oxide from insulating to half-metallic.Very recently unexpected ferromagnetism has been measured in thin films of undoped non-magnetic oxides, like HfO 2 and ZrO 2 , possibly assigned to the presence of lattice defects concentrated at the film interface. [8,9]. Here we prove the existence of a magnetization mechanism rooted in the loss of donor charge of the O atoms, something that can also occur in films with cation vacancies. This provides an explanation for the origin of the magnetic moments of these so called 'd-zero' ferromagnets. Furthermore, we predict that this kind of magnetism can be extended to a wider class of non-magnetic oxides, like MgO and Al 2 O 3 , where the cation is not necessarily...

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“…The reduction peak in the TPR pattern at 306°C is attributed to the reduction of bulk NiO [33] while the reduction peaks at 420-450°C were related to NiO x species that are having strong interaction with ZrO 2 [29,34]. The strong interaction between the nickel metal and the zirconia could be probably due to an increased interfacial area [29,34]. While in the case of reductive precipitation catalysts, no significant consumption of hydrogen was observed in their TPR profiles which clearly indicates that the Ni is in its metallic state.…”

Section: Temperature-programmed Reduction Studiesmentioning

confidence: 99%

“…Presence of strong chemical bonds between the Ni metal and the ZrO 2 has been revealed based on a DFT calculation by Beltran [33]. The reduction peak in the TPR pattern at 306°C is attributed to the reduction of bulk NiO [33] while the reduction peaks at 420-450°C were related to NiO x species that are having strong interaction with ZrO 2 [29,34]. The strong interaction between the nickel metal and the zirconia could be probably due to an increased interfacial area [29,34].…”

Section: Temperature-programmed Reduction Studiesmentioning

confidence: 99%

Nitrobenzene hydrogenation over Ni/TiO2 catalyst in vapour phase at atmospheric pressure: influence of preparation method

et al. 2015

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Highly dispersed nickel nanoparticles on supports such as ZrO 2 and TiO 2 were prepared by reductive deposition method using hydrazine as reducing agent and applied to nitrobenzene hydrogenation. The highlight of this work is to compare the characteristics and activity of these catalysts with the catalysts of the same composition prepared by impregnation method. All the catalysts were characterized by various techniques such as BET, H 2 pulse chemisorption, TEM, XRD (crystalline nature), reduction behaviour (TPR) and state of nickel species (XPS). Ni/ TiO 2 catalyst prepared by reductive deposition method shows excellent conversion of nitrobenzene (99 %) to aniline. This is due to the presence of higher number of surface Ni species than other catalysts as evidenced by H 2 -chemisorption. TPR results reveal the formation of metallic Ni species in the reductive deposition method. XRD results suggest that the all catalytic systems show peaks corresponding to the supports only and not due to the metallic Ni because of its presence in highly dispersed form. The decrease in catalytic performance is observed during the time on stream might be due to coking of the catalyst by the reaction intermediate.

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Bond formation at theNi/ZrO2interface

Cited by 74 publications

References 24 publications

Atomic and Electronic Structures of Ni/YSZ(111) Interface

Atomic and Electronic Structures of Ni/YSZ(111) Interface

Magnetism and half-metallicity at the O surfaces of ceramic oxides

Nitrobenzene hydrogenation over Ni/TiO2 catalyst in vapour phase at atmospheric pressure: influence of preparation method

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