Search results for "tetragonal crystal"
showing 10 items of 216 documents
Europium doped zirconia luminescence
2010
Abstract The luminescence properties and crystalline structure of ZrO2:Eu nanocrystals doped with different concentrations of Eu were studied. Luminescence from the Eu2+ state was not observed even if the electrons and holes were created up to ∼1019 cm−3; thus it was suggested the Eu3+ was not an efficient trap for electrons possibly due to Eu3+ negative charge relative to the crystalline lattice. The mutual interaction between Eu3+ ions was not strong up to 5 at.% concentration. The stabilization of ZrO2 tetragonal as well as cubic structure by Eu3+ is possible.
Crystal structure and phase transition of TlReO4: a combined experimental and theoretical study
2020
Abstract The present work describes a density-functional theory (DFT) study of TlReO4 in combination with powder x-ray diffraction experiments as a function of temperature and Raman measurements at ambient temperature. X-ray diffraction measurements reveal three different structures as a function of temperature. A monoclinic structure (space group P21/c) is observed at room temperature while two isostructural tetragonal structures (space group I41/a) are found at low- and high-temperature. In order to complement the experimental results first-principles DFT calculations were performed to compute the structural energy differences. From the total energies it is evident that the monoclinic str…
Local structure of gadolinium in oxyfluoride glass matrices containing SrF2 and BaF2 crystallites
2016
Abstract Gd3 + doped aluminosilicate oxyfluoride glasses and glass-ceramics containing SrF2 and BaF2 crystallites have been studied by differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopy techniques. A pronounced EPR fine structure emerges after the heat treatment of the glass matrix. EPR spectra simulations indicate the formation of cubic, tetragonal and trigonal Gd3 + centres in the studied compositions.
Synthesis, structure and spectroscopic properties of luminescent GdVO 4 :Dy 3+ and DyVO 4 particles
2018
Part of this research was done during visit of D.J. to IFN-CNR CSMFO Lab. and FBK Photonics Unit, Povo-Trento, Italy, in the framework of the STSM (Grant No. 38223) from the project: COST Action MP 1401 Advanced Fibre Laser and Coherent Source as tools for Society, Manufacturing and Lifescience” (2014e2018). The authors from Vinca Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Tech-nological Development of the Republic of Serbia (Project No: 45020 and 172056). L.T.N. Tran acknowledges the scholarship of the Ministry of Education and Training, Vietnam International Education Development. T. G. acknowledges the ERDF PostDoc project No…
Phase stability and oxygen-sensitive photoluminescence of ZrO2:Eu,Nb nanopowders
2018
This work was supported by institutional research funding ( IUT34-27 and IUT2-14 ) of the Estonian Ministry of Education and Research .
Dislocation interaction with C in α-Fe: a comparison between atomic simulations and elasticity theory
2008
International audience; The interaction of C atoms with a screw and an edge dislocation is modelled at an atomic scale using an empirical Fe-C interatomic potential based on the Embedded Atom Method (EAM) and molecular statics simulations. Results of atomic simulations are compared with predictions of elasticity theory. It is shown that a quantitative agreement can be obtained between both modelling techniques as long as anisotropic elastic calculations are performed and both the dilatation and the tetragonal distortion induced by the C interstitial are considered. Using isotropic elasticity allows to predict the main trends of the interaction and considering only the interstitial dilatatio…
Dielectric relaxation and polaronic hopping in Mn-substituted LaSrNiO4 nickelates prepared by mechanical milling method
2016
Abstract The structures, microstructures and dielectric properties of LaSrNi1−xMnxO4 (x = 0, 0.1, 0.2, 0.3 and 0.5) ceramics synthetized by mechanical milling followed by heat treatment were studied. One single tetragonal phase was revealed in all compounds. Structural parameters were obtained by Rietveld refinement. The substitution of Ni ions by Mn produces a variation of the lattice parameters but no phase change is observed. The surface morphology and elemental analysis of these samples were respectively investigated by Scanning Electron Microscopy (SEM) and energy dispersive X-ray technique (EDS). Giant dielectric response was observed in these ceramics, and at least two relaxations we…
Characterisation of scheelite LaW0.16Nb0.84O4.08 ion conductor by combined synchrotron techniques: Structure, W oxidation state and interdiffusion
2021
Abstract Scheelite-type materials such as LaNbO4 are increasingly attracting attention as a possible alternative to the most common fluorite and perovskite structure as ion conductors. However, they are much less used and investigated. The introduction of tungsten in lanthanum orthoniobate leads to conduction properties that are compatible with oxygen ion conductivity. In this paper, we studied the effect of the introduction of tungsten in the LaNbO4 structure. High resolution X-ray diffraction showed that in LaNb1-xWxO4+x/2 with x = 0.16 the monoclinic distortion is largely suppressed and the tetragonal phase is predominant at room temperature. By XANES/EXAFS we proved that tungsten is in …
Cathodoluminescence of crystalline and amorphous SiO2 and GeO2
2001
Abstract Cathodoluminescence (CL) and its temperature-dose behaviour are presented for different crystalline and amorphous modifications of SiO 2 and GeO 2 as well as for Ge-doped SiO 2 layers. The crystalline samples include four-fold coordinated Si and Ge in hexagonal quartz and quartz-like crystals, respectively, as well six-fold coordinated atoms in tetragonal rutile-like crystals. The detected luminescence bands, in general, are attributed to three optical active luminescence centres: the two-fold coordinated silicon (=Si:) and germanium (=Ge:) centre, respectively, the non-bridging oxygen hole centre (NBOHC) and the self trapped exciton (STE). The first ones, the oxygen deficient cent…
Stabilisation of tetragonal zirconia in oxidised ZrSiN nanocomposite coatings
2004
Abstract ZrSiN coatings were deposited on steel and silicon substrates by reactive sputtering of a composite ZrSi target. The coatings were oxidised in air in the 600–750 °C temperature range. As-deposited and oxidised films were characterised by X-ray diffraction, micro-Raman spectroscopy, X-ray photoemission spectroscopy and glow discharge optical emission spectroscopy. The oxidation behaviour of ZrSiN coatings was compared to that of ZrN ones. It was demonstrated that addition of silicon in the 3–5 at.% range into ZrN-based coatings promotes the onset of oxidation by nearly 100 °C. The structure of the oxide layer was strongly dependent on the film’s silicon content: monoclinic zirc…