Search results for "Grain Size"
showing 10 items of 131 documents
Effect of Reaction Parameters on Composition and Morphology of Titanate Nanomaterials
2009
International audience; In the present article, we report the synthesis of titanate nanotubes and nanoribbons with controlled morphology, structure, and chemical composition depending on the main parameters of the synthesis. Hydrothermal processing time, grain size of the precursor, type of agitation, and acid treatment were investigated, and the principal controversies mentioned in the literature such as nanotube crystallographic structure, their chemical composition, and acid treatment impact are discussed. These controversies may be due to the heterogeneities present in all the samples and are rarely considered in the literature. These nanostructures were characterized by Raman spectrosc…
Tritium localisation and release from the ceramic pebbles of breeder
2004
Magnetic field (MF) effects on the radiolysis and tritium release from Li4SiO4 (FZK) and Li2TiO3 (CEA) ceramic pebbles were investigated. The tritium chemical forms in Li4SiO4 were estimated by means of lyomethods. In the case of the neutron fluence Fn 6 10 18 nm � 2 , the tritium is mostly in the T þ form, but in the case of Fn � 10 25 nm � 2 , the T þ form accounts for 86–95% of the tritium. A high subsurface concentration of tritium is characteristic of a separate pebble and correlates with the distribution of radiation-induced defects. The MF increases the radiolysis of Li4SiO4 by 20–25%. Irradiation with electrons to 1000 MGy at 1200 K increases the grain size by 5–10%, decreasing the …
Dynamics of Polar Clusters in PMN Ceramics: Comparison with PMN Single Crystal
2006
The dielectric permittivity of PMN ceramics was measured in the frequency range from 20 Hz to 37 GHz. From the frequency dependence of the real and imaginary parts of dielectric permittivity, the distribution of relaxation times f(τ) was calculated. The f(τ) function broadens significantly, and the second maximum appears below the 270 K temperature. The dielectric response and also relaxation time distribution of PMN ceramics was compared with the previous results of PMN single crystal. The results showed that dynamics of polar nano regions in PMN ceramics is suppressed due to the small size of grains in the ceramics.
BST ceramics: Effect of attrition milling on dielectric properties
2004
Abstract The effect of grain size on the dielectric properties of Ba0.6Sr0.4TiO3 (BST) ceramics is investigated. Attrition milling is chosen to obtain nanometre particle size from micrometre particle size powders. Fine grained ceramics are obtained by hot uniaxial pressing (HUP). Additionally, the present study is focused on the effect of the nature of milling balls on loss tangent and permittivity. For that, three kinds of balls are tested: calcia, yttria or ceria stabilised zirconia balls. The properties of these samples are evaluated in the range of MHz. The balls induce an involuntary doping of powders which modifies the dielectric properties, especially the Curie temperature and loss t…
Up-conversion luminescence dependence on structure in zirconia nanocrystals
2013
The zirconia samples containing two different concentrations of Er and Yb dopants were prepared using the Sol–Gel method and up-conversion luminescence was studied using the time-resolved techniques. The up-conversion luminescence depends on the oxygen content in surrounding gasses during annealing as well as on the annealing temperature. These dependencies indicate that ZrO2 intrinsic defects annealing and generation, phase transition as well as dopant redistribution take place. The possible role of these processes on up-conversion luminescence is discussed. The results of experiments confirmed that the annealing temperature has a crucial influence on up-conversion luminescence for samples…
Dielectric Properties of Na0.5K0.5(Nb1-xSbx)O3+MnO2 Ceramics (x = 0.04, 0.05 and 0.06)
2011
Lead-free ceramics Na0.5K0.5(Nb1-xSbx)O3+0.5mol%MnO2 (x = 0.04, 0.05 and 0.06) were prepared by conventional sintering and hot pressing process; their microstructure and dielectric properties have been studied. It is found that increase of sintering temperature promotes the obtaining highly dense microstructure and increase in grain size while doping with Sb contributes to more dense and homogeneous microstructure and smaller grain size. Low frequency (100 Hz-200 kHz) investigations revealed the diffuse phase transitions. It can be concluded from experimental results that Sb doping improves dielectric properties. The obtained materials are expected to be promising candidates for lead-free e…
Thermodynamic considerations of the grain size dependency of material properties
1994
Phase transitions which depend on grain size induce very interesting properties in materials such as zirconia or barium titanate. A new and rigorous thermodynamic treatment of this type of phase transition is proposed with consideration of the surface phenomena. An interpretation is given of the observed differences when the material—particularly BaTiO3—under consideration is a fine grain powder or is a fine grain ceramic.
Photoluminescence in AlN: macro‐size and nano‐powder
2007
Photoluminescence (PL) properties in AlN are studied when size of polycrystalline grains is reduced from macro-size (AlN ceramics and macro-size powder) to nano-size (nano-powder). It was found that in all these materials within the UV- blue spectral region two PL bands are observed at ∼400 nm (caused by the oxygen-related defects) and at 480 nm (with unknown defect structure) but the ratio of their intensities depends on the grain size. Reduction of AlN grain size results in decrease of the 400 nm band and increase of the 480 nm band. It allows the following conclusions: i) reduction of AlN grain size results in decrease of oxygen (the native impurity of AlN) content in the crystalline lat…
Excitonic luminescence in ZnO nanopowders and ceramics
2009
Abstract Fast photoluminescence spectra in the spectral region of 3.1–3.45 eV in ZnO and ZnO:Al ceramics were studied at 14 and 300 K. Ceramics with grains smaller than 100 nm were sintered from nanopowders by high pressure (8 GPa) and low temperature (350 °C). Ceramics with grain sizes 1–5 μm were sintered at 1400 °C. It is shown that excitonic luminescence spectra depend on the ceramics grain size, post preparing annealing and doping. The excitonic luminescence decay time was faster than 2 ns and the afterglow at 30 ns was ∼0.05%.
Study on Structural, Mechanical, and Optical Properties of Al2O3–TiO2 Nanolaminates Prepared by Atomic Layer Deposition
2015
Structural, optical, and mechanical properties of Al2O3/TiO2 nanolaminates fabricated by atomic layer deposition (ALD) were investigated. We performed transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray reflectivity (XRR), energy dispersive X-ray spectroscopy (EDX), ellipsometry, UV–vis spectroscopy, photoluminescence (PL) spectroscopy, and nanointendation to characterize the Al2O3/TiO2 nanolaminates. The main structural, optical, and mechanical parameters of Al2O3/TiO2 nanolaminates (thickness, grain size, refractive index, extinction coefficient, band gap, hardness, and Young’s module) were calculated. It was established that with decreasing of the layer thickness, the …