Search results for "Crystallite"
showing 10 items of 347 documents
Ab initiocomputational study on the lattice thermal conductivity of Zintl clathrates[Si19P4]Cl4andNa4[Al4Si19]
2016
The lattice thermal conductivity of silicon clathrate framework ${\mathrm{Si}}_{23}$ and two Zintl clathrates, $[{\mathrm{Si}}_{19}{\mathrm{P}}_{4}]{\mathrm{Cl}}_{4}$ and ${\mathrm{Na}}_{4}[{\mathrm{Al}}_{4}{\mathrm{Si}}_{19}]$, is investigated by using an iterative solution of the linearized Boltzmann transport equation in conjunction with ab initio lattice dynamical techniques. At 300 K, the lattice thermal conductivities for ${\mathrm{Si}}_{23}, [{\mathrm{Si}}_{19}{\mathrm{P}}_{4}]{\mathrm{Cl}}_{4}$, and ${\mathrm{Na}}_{4}[{\mathrm{Al}}_{4}{\mathrm{Si}}_{19}]$ were found to be 43 W/(m K), 25 W/(m K), and 2 W/(m K), respectively. In the case of ${\mathrm{Na}}_{4}[{\mathrm{Al}}_{4}{\mathrm…
Up-conversion luminescence of GdVO4:Nd3+/Er3+ and GdVO4:Nd3+/Ho3+ phosphors under 808 nm excitation
2018
All authors acknowledge to the COST Action CM1403: The European upconversion network - from the design of photon-upconverting nanomaterials to biomedical applications (2014–2018). The authors from the University of Belgrade acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ). K. S. acknowledges the Latvian National Research Program IMIS2 (Grant No. 302/2012 ). T. G. acknowledges the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ).
Phase transformation in a glass-ceramic observed by laser spectroscopy
1988
The influence of thermal treatment on a (Li2O∶Al2O3∶ SiO2) glass ceramic is studied by laser spectroscopy. At temperatures above 800 °C a fluorescence of Cr3+ ions around 693 nm appears which indicates the growth of crystallites where the Cr3+ ions occupy sites similar to those in Al2O3.
Modeling of anisotropic grain growth in minerals
2001
The role of surface energy anisotropy during grain growth is investigated using both physical experiments on octachloropropane and numerical experiments using the Elle microstructural modelling system. In particular the effects of anisotropy on growth rates, grain shapes and lattice preferred orientations are analysed. Anisotropic growth in thin polycrystalline sheets of octachloropropane is found to systematically remove certain c-axis orientations from the sample, without obviously modifying the grain shapes. By comparison with equivalent numerical experiments, we can explain these observations with a simple boundary layer model that treats each side of each grain boundary as an independe…
Intergrain Effects in the AC Susceptibility of Polycrystalline LaFeAsO_{0.94}F_{0.06}
2010
The AC susceptibility, chi, at zero DC magnetic field of a polycrystalline sample of LaFeAsO_{0.94}F_{0.06} (Tc ≈ 24 K) has been investigated as a function of the temperature, the amplitude of the AC magnetic field (in the range Hac = 0.003 Oe - 4 Oe) and the frequency (in the range f = 10 kHz - 100 kHz). The chi(T) curve exhibits the typical two-step transition arising from the combined response of superconducting grains and intergranular weak-coupled medium. The intergranular part of chi strongly depends on both the amplitude and the frequency of the AC driving field, from few Kelvin below Tc down to T = 4.2 K. Our results show that, in the investigated sample, the intergrain critical cur…
Raman scattering in nanosized nickel oxide NiO
2007
Magnetic ordering in nanosized (100 and 1500 nm) nickel oxide NiO powders, prepared by the plasma synthesis method, was studied using Raman scattering spectroscopy in a wide range of temperatures from 10 to 300 K. It was observed that the intensity of two- magnon band decreases rapidly for smaller crystallites size. This effect is attributed to a decrease of antiferromagnetic spin correlations and leads to the antiferromagnetic-to- paramagnetic phase transition .
Up-conversion process in erbium doped lithium fluoride bulk crystal, lithium borate glass and glass ceramics
2007
In our research the up-conversion processes in Er doped bulk LiF crystal, lithium borate oxyfluoride glass and lithium borate oxyfluoride glass ceramics were studied: up- conversion and traditional photoluminescence spectra, the up-converted signal as a function of the laser power are presented. It was found that sharp luminescence bands in the visible part of the spectrum appear when the bulk crystal is subjected to IR irradiation at 980 nm by a laser diode. After the heat treatment of the glass submicron crystallites were detected by SEM technique. The presence of LiF crystalline phase in the oxyfluoride glass ceramics was proved by XRD method. The questions about the synthesis of the oxy…
Zn K-edge XANES in nanocrystalline ZnO
2007
Zn K-edge XANES in ZnO has been calculated within the full-multiple-scattering (FMS) and finite difference method (FDM) formalism using the ab initio FDMNES code. The influence of non-muffin-tin potential, bulk defects, surface termination and polarization effects on XANES has been analysed. The obtained theoretical results are compared with available experimental data for polycrystalline and nanocrystalline zinc oxide systems.
In situ measurement of elastic properties of PdH , PdD , and PdT
2003
Abstract The Young’s modulus E of palladium hydride PdH x , deuteride PdD x and tritide PdT x were measured for studying the effect of both hydrogen stoichiometry x and isotope nature. A special technique based on optical detection of flexural modes of a palladium cylindrical microcantilever was adapted to in situ measurements to guarantee the sample homogeneity during the hydriding process. A 10% decrease in E was found between pure polycrystalline palladium and hydride phases. The non linear dependence observed with the H content was discussed in terms of lattice expansion, phonons and electronic properties. Sensitivity of the technique enables to distinguish an isotope effect on E .
Sorption Studies on Large ZSM-5 Crystals: The Influence of Aluminium Content, The Type of Exchangeable Cations and the Temperature on Nitrogen Hyster…
1988
Abstract In comparison to polycrystalline powder large ZSM-5 crystals are best suited for high resolution sorption experiments. The nitrogen isotherms on HZSM-5 at 77 K reveal a pronounced hysteresis loop. The shape and position of the hysteresis relative to the pressure axis has been found to be affected by the aluminium content of the zeolite, the type of framework cation and the sorption temperature. The occurence of the hysteresis and its changes are assigned to a transition from a liquidlike to a solid-like adsorbed phase of nitrogen. The micropore volume v mp derived from the argon and nitrogen isotherm (s. Fig. 2b, first plateau) and calculated according to DUBININ-RADUSHKEVICH was c…