Search results for " Boundary"
showing 10 items of 686 documents
Mn2+-induced room-temperature ferromagnetism and spin-glass behavior in hydrothermally grown Mn-doped ZnO nanorods
2014
The magnetic properties of Mn-doped ZnO (ZnO:Mn) nanorods grown by hydrothermal process at a temperature of 200 °C and a growth time of 3 h have been studied. The samples were characterized by using powder X-ray diffraction with Rietveld refinement, scanning electron microscopy, energy-dispersive X-ray analysis and SQUID magnetometry. Mn (3 wt%) and (5 wt%)-doped ZnO samples exhibit paramagnetic and ferromagnetic behavior, respectively, at room temperature. The spin-glass behavior is observed from the samples with respect to the decrease of temperature. At 10 K, both samples exhibit a hysteresis loop with relatively low coercivity. The room-temperature ferromagnetism in 5 wt% Mn-doped ZnO n…
Study of the Dielectric Properties of Europium Doped Barium Titanate Ceramics by an Impedance Spectroscopy
2015
The barium titanate (BaTiO3) and the BaTiO3 + 0.1wt.% Eu2O3 ceramics were prepared by a conventional ceramic method. The structural studies were carried out by means of an X-ray diffraction technique. The influence of the grains and the grain boundaries on the electrical properties was investigated using a impedance spectroscopy. This technique enables us to determine the values of grain and grain boundary resistance. The results show that the Eu doping leads to a significant reduction in the resistance value of the grains (˜105Ω) with respect to the pure BT ceramics (˜107Ω). The conductivity processes were determined from the Arrhenius behaviour of grain and grain boundary resistances.
Effects of Grain Boundary Decoration on the Electrical Conduction of Nanocrystalline CeO2
2012
In this study, we investigate the effect of decorating the grain boundaries of nanocrystalline undoped ceria on the electrical transport properties. For the decoration, different acceptors (Yb, Y, Bi) were chosen. On decoration, the conduction switches from electronic to ionic. Upon sintering the grains are characterized by a core-shell configuration, in which the core remains undoped while the shell is heavily doped as a consequence of the diffusion of the acceptors toward the grain interior. The shell dominates the overall transport properties of the nanocrystalline ceria and is found to be in the mesoscopic regime.
The combined effect of refractory coatings containing reactive elements on high temperature oxidation behavior of chromia-forming alloys
2003
Abstract The high temperature oxidation behaviors of chromia-forming alloys (F17Ti and Fe–30Cr alloys) have been studied at 1273 K under isothermal conditions and at 1223 K under cyclic conditions, in air under the atmospheric pressure. To extend the oxidation lifetime, coatings have been applied onto the alloy surfaces. Al2O3 and Cr2O3 films doped with Sm2O3 or Nd2O3 were prepared via the metal-organic chemical vapor deposition technique. Single Cr2O3, Al2O3, Nd2O3 and codeposited Cr2O3–Nd2O3, Al2O3–Nd2O3, Al2O3–Sm2O3 coatings drastically improved the chromia-forming alloy high temperature oxidation behavior, since they decreased the oxidation rate and enhanced the oxide scale adhesion. Re…
Ultrafast luminescence of Ga- and In-doped ZnO ceramics
2021
The work of authors (a-c) was financially supported by Russian Foundation for Basic Research (RFBR, Russia) and the work of the last author (d) had financial support from State Education Development Agency (VIAA, Latvia) . All of that was approved as a result of ERA.Net RUS PLUS 2017 joint call for proposals. Here is the link for the joint call for reference: https://www.eranet-rus.eu/en/196.php .
A three-dimensional grain boundary formulation for microstructural modeling of polycrystalline materials
2013
Abstract A three-dimensional grain boundary formulation is presented for the analysis of polycrystalline microstructures. The formulation is based on a boundary integral representation of the elastic problem for the single grains of the polycrystalline aggregate and it is expressed in terms of the intergranular fields, namely displacements and tractions, that play an important role in polycrystalline micromechanics. The artificial polycrystalline morphology is represented using the Hardcore Voronoi tessellation, which is simple to generate and able to embody the main statistical features of polycrystalline microstructures. The details of the microstructure generation and meshing, which invo…
Relation between grain size and hydrogen diffusion coefficient in an industrial Pd–23% Ag alloy
1999
Abstract The diffusion mechanism of hydrogen in an industrial cold worked Pd–23% Ag alloy is investigated according to its grain size. The microstructural parameters are determined by X-ray diffraction analysis and the diffusion parameters are determined using the galvanostatic electrochemical permeation technique. Two diffusion mechanisms are displayed. For apparent grain size below 40 nm the hydrogen atoms diffuse in the grain boundaries. For grain size above 100 nm, an intergranular diffusion mechanism occurs. For intermediate grain size both mechanisms coexist. Furthermore, the diffusion in the grain boundaries is not faster than the diffusion in the bulk, as generally observed for pure…
Modelling intergranular and transgranular micro-cracking in polycrystalline materials
2018
Abstract In this work, a grain boundary formulation for intergranular and transgranular micro-cracking in three-dimensional polycrystalline aggregates is presented. The formulation is based on the displacement and stress boundary integral equations of solid mechanics and it has the advantage of expressing the polycrystalline problem in terms of grain boundary variables only. The individual grains within the polycrystalline morphology are modelled as generally anisotropic linear elastic domains with random spatial orientation. Transgranular micro-cracking is assumed to occur along specific cleavage planes, whose orientation in space within the grains depend upon the crystallographic lattice.…
Phonon Bridge Effect in Superlattices of Thermoelectric TiNiSn/HfNiSn With Controlled Interface Intermixing
2020
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A grain boundary formulation for crystal plasticity
2016
Abstract A three-dimensional grain-boundary formulation for small strains crystal plasticity is presented for the first time. The method is developed and implemented for both single grains and polycrystalline aggregates and it is based on the use of a suitable set of boundary integral equations for modelling the individual grains, which are represented as anisotropic elasto-plastic domains. In the boundary integral framework, crystal plasticity is modelled resorting to an initial strains approach and specific aspects, related to the integration of strongly singular volume integrals in the anisotropic elasto-plastic grain-boundary equations, are discussed and suitably addressed for the first…