Search results for "Yttrium"
showing 10 items of 179 documents
Effects of Thermal Treatment on the Structure of Eu:YAG Nanopowder
2007
Eu:YAG nanopowder precursors were obtained by co-precipitation of aluminium, yttrium and europium nitrates solution with ammonia. The hydroxides precursors were calcined at different temperatures from 900 to 1200°C as a function of holding time (1, 2 and 6 hours). The presence of Eu3+ ions in the matrix was confirmed by Energy Dispersive X-rays analysis. X-Ray Diffraction investigation by the Rietveld method shows that the sample treated at 900°C for 1 hour is essentially the garnet phase with the minor presence of hexagonal and monoclinic metastable phases. The Eu3+ ions are incorporated into the garnet phase, as is suggested by the lattice parameter value being larger than that in literat…
Antiferromagnetic NiO thickness dependent sign of the spin Hall magnetoresistance in γ-Fe2O3/NiO/Pt epitaxial stacks
2019
We study the spin Hall magnetoresistance (SMR) in epitaxial γ–Fe2O3/NiO(001)/Pt stacks, as a function of temperature and thickness of the antiferromagnetic insulating NiO layer. Upon increasing the thickness of NiO from 0 nm to 10 nm, we detect a sign change of the SMR in the temperature range between 10 K and 280 K. This temperature dependence of the SMR in our stacks is different compared to that of previously studied yttrium iron garnet/NiO/Pt, as we do not find any peak or sign change as a function of temperature. We explain our data by a combination of spin current reflection from both the NiO/Pt and γ-Fe2O3/NiO interfaces and the thickness-dependent exchange coupling mode between the …
Thermomechanical properties and thermal degradation kinetics of poly(methyl methacrylate) (PMMA) and polycarbonate (PC) filled with cerium-doped yttr…
2016
This paper reports on the thermomechanical properties and thermal degradation kinetics of poly(methyl methacrylate) (PMMA) and polycarbonate (PC) composites filled with cerium-doped yttrium aluminium garnet (Ce:YAG) at different contents ranging between 0.1 and 5 wt%, and prepared by melt compounding. The interaction between PMMA and the filler was much stronger than that between PC and the filler, and this resulted in a significant improvement in the dynamic mechanical properties of the PMMA composites. The presence of filler did not significantly increase the thermal stability of the PC, while an observable increase in the thermal stability was only observed at higher filler loadings for …
Defect Calculations for Yttrium Aluminum Perovskite and Garnet Crystals
2000
Native and impurity point defects in both Yttrium Aluminum Perovskite and Garnet crystals are studied in the framework of the pair-potential and the shell model approximations. The calculated formation energies for native defects suggest that the antisite disorder is preferred over the Frenkel and Schottky-like disorder in both YAP and YAG. In non-stoichiometric compounds, the calculated reaction energies indicate that excess of Y2O3 or Al2O3 is, most likely, to be accommodated by the formation of antisites rather than vacancies or interstitials in the lattice. Enthalpies of the reactions for impurity (Ca2+, Mg2+, Sr2+, Ba2+, Cr3+, Fe3+, Nd3+, Si4+) incorporation into both YAP and YAG latti…
Microwave synthesis of yttria stabilized zirconia
2005
Yttria stabilised zirconia (YSZ) nanocrystals, with a mean size between 5 and 10 nm, were prepared by microwave flash synthesis. Flash synthesis was performed in alcoholic solutions of yttrium, zirconium chloride and sodium ethoxide (EtONa) using a microwave autoclave (RAMO system) specially designed by authors. Energy dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), BET adsorption technique, photon correlation spectroscopy (PCS) transmission and scanning electron microscopy (TEM and SEM) are used to characterized these nanoparticles. Compared with conventional synthesis, nanopowders can be produced in a short period (e.g. 10 s), both high purity and stoechiometric control a…
Sol-gel assisted molten-salt synthesis of novel single phase Y3–2xCa2xTaxAl5−xO12:1%Eu garnet structure phosphors
2022
Strong absorption and emission are the key the features of any phosphor. The results obtained during this study demonstrate the difficulty of the incorporation of tantalum ions into the garnet structure and reveal that only the combination of Sol-Gel synthesis method together with Molten-Salt technique enable to obtain a single-phase cubic garnet structure. Note that, the Sol-Gel synthesis assisted by further processing by Molten-Salt technique can be a potentially new way of material preparation reported in literature. This work also proves that this combination of synthesis methods is much more capable of incorporating ions with large ionic radii into the garnet structure as compared to t…
Influence of vinyltriethoxysilane concentration on structural and luminescent characteristics of cerium doped yttrium based silicate phosphors
2015
Abstract Cerium doped yttrium silicates phosphors (YSO:Ce) were prepared by gel combustion using vinyltriethoxysilane (VTEOS) as silicon sources along with aspartic acid as fuel and yttrium-cerium nitrate as oxidizer. The study presents the influence of VTEOS amount in the synthesis mixture on the structural and luminescent characteristics of silicate phosphors. The understanding of precursor׳s decomposition was achieved on the basis of thermal analysis in association with gas evolved analysis. XRD, FTIR and XPS were used to reveal the structural changes that occur with VTEOS molar amount variation from 1 to 3 mol. It was found that the main crystalline phase was X2-Y 2 SiO 5 . The luminesc…
Co-precipitation synthesis of neodymium-doped yttrium aluminium oxides nanopowders: Quantitative phase investigation as a function of joint isotherma…
2007
Abstract Neodymium-doped yttrium aluminium nanopowders with nominal Nd:Y:Al ratio equal to X:3–X:5 (where X = 0, 0.006, 0.012, 0.024, 0.048, 0.081, 0.096, 0.171, 0.192, 0.384, 0.540 and 0.720) were prepared by the co-precipitation method and subjected to five cumulative stages of isothermal treatment in the temperature range from 900 to 1050 °C. The phase evolution of the oxides were investigated quantitatively by the X-ray powder diffraction approach using the Rietveld method of analysis. An almost single phase cubic garnet structure was attained at temperatures as low as 900 °C for specimens with neodymium loading less than ca. 6 at.% with respect to total (Nd + Y) atoms. Isothermal treat…
Raman Studies of Photorefractive Lithium Niobate Single Crystals
2014
A study of Raman spectra of lithium niobate single crystals: stoichiometric, ostensibly pure congruent LiNbO3, and congruent LiNbO3 containing admixture of yttrium is reported. Raman bands observed in spectra excited by visible laser radiation are thoroughly compared to the same bands excited by infrared laser radiation. The broadening of Raman bands excited by radiation of shorter wavelengths is attributed to photo-refraction induced by visible radiation (514 nm) while being absent under infrared radiation (1064 nm). Attributing the effect of photo-refraction to radiation-induced structural changes in the illuminated part of the crystal lattice the authors interpret the observed broadening…
Reduction of temperature coefficients in multicrystalline silicon solar cells after light-induced degradation
2015
This study focuses on the variations of the temperature coefficients after light-induced degradation (LID) of compensated multicrystalline silicon solar cells from three different ingots. The ingots have been chosen to see the effect of the compensation level, the resistivity and the impact of adding gallium to keep the resistivity as constant as possible along the ingot. The temperature coefficients of the efficiency experience a major decrease after LID on all ingots. We found that this decrease varies along the ingot height and does not correspond to the VOC drop. Moreover, no direct correlation with the interstitial oxygen concentration profiles could be seen.