The paper deals with ab initio investigations of elastic and photoelastic properties of oxides and nitrates of alkaline-earth metals. In gradient approximation of the density functional theory (DFT), these properties are studied with the use of the linear combination of the atomic orbital technique. DFT calculations are done with the CRYSTAL 14 software package. The paper introduces the elastic and photoelastic constants, anisotropy parameters for single-crystalline phases and the elastic modules, hardness, Poisson ratio for polycrystalline phases. Such parameters as sonic speed, Debye temperature, thermal conductivity, and Gruneisen parameter are estimated herein. For the fist time, mechanical stability, anisotropy of elastic and photoelastic properties and their dependences are investigated ab initio in this paper. Experimental results on elastic and photoelastic properties of oxides and nitrates are in good agreement with theoretical calculations.
In this work, aluminate type phosphorescence materials were synthesized via the solid state reaction method and the photoluminescence (PL) properties, including excitation and emission bands, were investigated considering the effect of trace amounts of activator (Eu3+) and co-activator (Dy3+). The estimated thermal behavior of the samples at certain temperatures (> 1000 degrees C) during heat treatment was characterized by differential thermal analysis (DTA) and thermogravimetry (TG). The possible phase formation was characterized by X-ray diffraction (XRD). The morphological characterization of the samples was performed by scanning electron microscopy (SEM). The PL analysis of three samples showed maximum emission bands at around 610 nm, and additionally near 589 nm, 648 nm and 695 nm. The bands were attributed to typical transitions of the Eu3+ ions.
The phase equilibria for the MCI2-ThCI4(M: Mg, Ca, Sr, Ba) binary systems were critically evaluated and optimized based upon the CALPHAD approach.. The substitutional solution model(SSM) was used to describe the liquid phase. All the. intermediate compounds were treated as stoichiometric compounds of which Gibbs energies comply with the Neumann-Kopp rule. Thermodynamic model parameters optimization for respective phases was conducted by the least squares minimization procedure with required input data available from experimental measurements. Satisfactory agreements between all calculated results and experimental data were achieved which demonstrates that thermodynamic databases for the MCI2-ThCI4(M: Mg, Ca, Sr, Ba) binary systems were ultimately derived. in the present work allowing safe extrapolation into multi-component system for guiding relative industrial applications.
Catalytic fast pyrolysis analysis of miscanthus over HZSM-5, La/ZSM-5, and Ca/ZSM-5 was performed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The characteristics of the catalysts used in this study were analyzed using XRD, SEM, Pyridine IR, ICP, and N-2 adsorption. The catalytic performance of the three catalysts was evaluated in terms of deoxygenation. Py-GC/MS results show that with increasing temperature, pyrolysis vapor yield first increased and then decreased. This may be due to secondary cracking at higher temperatures, which produced more gas products. Moreover, hydrocarbon content increased with rising temperature. The optimum temperature was found to be 600 A degrees C, which resulted in the greatest liquid yield. All three catalysts increased pyrolysis vapor yield by about 30 %. Moreover, the hydrocarbon content of miscanthus increased from 6 to 39 %, 46, and 44 %, respectively, when HZSM-5, La/ZSM-5, and Ca/ZSM-5 were applied. In conclusion, the three catalysts were effective for deoxygenation of pyrolysis vapor yield. Considering both economic and catalytic upgrading effect, Ca/ZSM-5 may be the best catalyst.
Sun Woog Kima
Green-emitting (La1?/sub>x?/sub>yMxTby)OCl (0 ?#xA0;x ?#xA0;0.13, 0.03 ?#xA0;y ?#xA0;0.15, M = Mg, Ca, and Sr) single phase phosphors were synthesized using a liquid-phase method and their photoluminescence properties were characterized. The excitation spectrum consisted of a strong broad band from 220 to 290 nm, which corresponds to the 4f-5d transition of Tb3+. The oxychloride phosphors exhibit typical emission peaks assigned to the transition from 5D4 to 7FJ (J = 6, 5, 4, and 3) of Tb3+, and the luminescence emission intensity was successfully enhanced by doping divalent alkaline earth metal ions (M = Mg2+, Ca2+, and Sr2+) into La3+ sites of the host LaOCl lattice. The highest green emission intensity was obtained for (La0.88Ca0.05Tb0.07)OCl, of which the relative emission intensity was 75% of that for a commercial green-emitting (La0.52Ce0.31Tb0.17)PO4 phosphor.
This work presents a thermodynamic evaluation of the Ca(NO3)(2)-MNO3 (M: Li, Na, K, Rb, Cs) binary systems using the CALPHAD approach. The required Gibbs energy of liquid Ca(NO3)(2) is missing in the literature and has been successfully evaluated in the present work with a fusion enthalpy of 23849 J mol(-1). The substitutional solution model can thus be employed to describe the Ca(NO3)(2)-base liquid phase. All the intermediate compounds are treated to be stoichiometric and their Gibbs energies comply with the Neumann -Kopp rule. Empirical functions relating mixing enthalpies to ionic parameters are employed to predict the corresponding values of binary melts which are used as input data to assist in parameters optimization for the liquid phases. The final calculated results show good agreement with most of the experimental and predicted data.
Kim, Sun Woog
Green-emitting (La1-x-yMxTby)OCl (0 <=3D x <=3D 0.13, 0.03 <=3D y <=3D 0.15, M =3D Mg, Ca, and Sr) single phase phosphors were synthesized using a liquid-phase method and their photoluminescence properties were characterized. The excitation spectrum consisted of a strong broad band from 220 to 290 nm, which corresponds to the 4f-5d transition of Tb3+. The oxychloride phosphors exhibit typical emission peaks assigned to the transition from D-5(4) to F-7(J) (J =3D 6, 5, 4, and 3) of Tb3+, and the luminescence emission intensity was successfully enhanced by doping divalent alkaline earth metal ions (M =3D Mg2+, Ca2+, and Sr2+). into La3+ sites of the host LaOCl lattice. The highest green emission intensity was obtained for (La0.88Ca0.05Tb0.07)OCl, of which the relative emission intensity was 75% of that for a commercial green-emitting (La0.52Ce0.31Tb0.17)PO4 phosphor. (C) 2012 Elsevier B.V. All rights reserved.
Gardner, Adrian M.
Graneek, Jack B.
Breckenridge, W. H.
Wright, Timothy G.
Ab initio calculations were employed to investigate M+-RG2 species, where M+ =3D Ca, Sr, Ba, and Ra and RG =3D He-Rn. Geometries have been optimized, and cuts through the potential energy surfaces containing each global minimum have been calculated at the MP2 level of theory, employing triple-zeta quality basis sets. The interaction energies for these complexes were calculated employing the RCCSD(T) level of theory with quadruple-zeta quality basis sets. Trends in binding energies, D-e, equilibrium bond lengths, R-e, and bond angles are discussed and rationalized by analyzing the electronic density. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are presented. It is found that some of these complexes involving the heavier group 2 metals are bent whereas others are linear, deviating from observations for the corresponding Be and Mg metal-containing complexes, which have all previously been found to be bent. The results are discussed in terms of orbital hybridization and the different types of interaction present in these species.
Mi, Xiaoyun; Shi, Hui; Wang, Zan; Xie, Lingjie; Zhou, Hongyan; Su, Jiangang; Lin, Jun
In this paper, M-3(VO4)(2):Eu3+(M =3D Ca, Sr, Ba) phosphors have been synthesized by high-temperature solid-state method. The phase composition and luminescence properties of the synthesized phosphors were characterized by X-ray powder diffraction and photoluminescence (PL) spectra, respectively. The influences of fluxing agent and doped concentration of rare-earth ions on PL properties of the phosphor were investigated. The results indicated that the energy transfers between VO4 (3-) and Eu3+ in the host occurred mainly via a dipole-dipole interaction mechanism. The increase in cation radius (from Ca2+ to Ba2+) in the host causes the emission peak originated from D-5(0) -> F-7(2) transition of Eu3+ shifting from 615 to 621 nm, as well as decreasing the fluorescence lifetimes of Eu3+ from 0.77 to 0.19 ms and changing the CIE chromaticity coordinates from the orange-red region to the white region. Moreover, the emission colors of Ba3-x (VO4)(2):xEu(3+) can be firstly adjusted from cyan region to white light region via controlling the concentration of Eu3+. Temperature-dependent luminescence spectra proved the good thermal stability of the as-prepared phosphor. This work shows the potential application of europium-doped samples in UV converted pc-WLEDs.
Bi-doped MO-B2O3 (M=Ca, Sr, Ba) glasses were prepared by melting method. Excitation spectra, visible and infrared luminescence spectra were measured. Near infrared (NIR) emissions located at about 1190 nm with FWHM only 40 nm and at 1300 nm with FWHM about 200 nm can be observed in different samples when excited by 808 nm LD excitation. The two emission bands have different excitation bands. Red emission centered at 660 nm related to Bi2+ can be observed in some samples. The NIR emission at 1300 nm band disappears with the increase of optical basicity, while that of the NIR emission at 1190 nm band shows a contrary tendency. We proposed that the NIR emissions located at 1190 nm and 1300 nm originated from different bismuth centers. The infrared emission peak at about 1300 nm derives from low valence Bi ions according to the Duffy’s theory of optical basicity.
Substitution of Ca2+ and Sr2+ at the A-site of multiferroic TbMnO3 bulk results in an increased average ionic radius and ionic-size mismatch, and was found to reduce the orthorhombic distortion. Signatures of long-range ferromagnetic-like ordering at 78 K in Tb0.67Ca0.33MnO3 and at 87 K in Tb0.67Sr0.33MnO3 samples are clearly observed in both the dc and ac susceptibility data. A compensation temperature is also observed in Tb0.67Ca0.33MnO3, indicating the antiparallel alignment of Tb3+ moments to the Mn3+-Mn4+ moments. The canted antiferromagnetic ordering coexists with antiferromagnetic clusters, resulting in spin-glass-like behavior at low temperatures. An increased average ionic radius and ionic-size mismatch at the A-site are determined to be critical factors in determining the magnetic properties of the hole-doped manganites.