- Chemical vapour transport of ternary oxides in the systems Ca/Mo/O and Sr/Mo/O
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The chemical vapour transport behaviour of ternary phases in the Ca/Mo/O and Sr/Mo/O systems has been investigated using Cl2 as transport agent in a temperature gradient 1423 to 1323 K. MMoO4 (M= Ca, Sr) migrate in the above-mentioned temperature gradient with rates of 0.1 to 0.2 mg/h. Starting from three phase mixtures crystals of the compounds MMo 5O8 have been grown (migration rates: M = Ca 0.1 mg/h, M = Sr 0.01 mg/h). The observed transport behaviour is compared with predictions given by thermo dynamical model calculations and the influences of source composition and the moisture contents are described in detail.
- Steiner, Udo,Reichelt, Werner
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- ELECTRICAL CONDUCTIVITY OF CaMoO4 .
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The electrical conductivity and ionic transport number of CaMoO//4 has been measured as a function of the partial pressure of oxygen (1-10** minus **1 **8 atm) at 750, 800, and 850 degree C. Two sets of samples were studied: (1) CaMoO//4 annealed at 1100 degree C in the presence of CaO, and (2) CaMoO//4 annealed in MoO//3 vapor at 1100 degree C. Sample 1 is a mixed ionic/electronic conductor while Sample 2 is essentially an electronic conductor. A defect structure model is proposed to explain the results.
- Petrov,Kofstad
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- Photophysical and photocatalytic properties of Ca1-xBi xvxMo1-xO4 solid solutions
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New solid solutions with the composition of Ca1-xBi xVxMo1-xO4 prepared by a solid-state method were found as novel photocatalysts with enhanced activity for O 2 evolution from aqueous solu
- Yao, Weifeng,Ye, Jinhua
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- Self-assembly and photoluminescence characterization of CaMo O4: Eu3+, Na+ superstructure via a facile surfactant-free hydrothermal method
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The Eu3+, Na+ -codoped CaMo O4 microphosphors were successfully synthesized at low temperature via a facile hydrothermal method in a surfactant-free environment. Scanning electron microscopy, field-emission scanning electron microscope, and transmission electron microscopy images of the CaMo O4 products prepared at 150°C for 6 h revealed three dimensional flake-ball and flake-disk superstructures, composed of densely packed nanoflakes. The formation mechanism of CaMo O4 microstructures was discussed in detail based on the hydrothermal temperature. Meanwhile, other influencing factors on the morphology were also reported. Room-temperature photoluminescence properties of microsized CaMo O4: Eu3+, Na+ phosphors were studied. Its excitation wavelengths ranging from 350 to 530 nm in the ultraviolet and visible regions significantly extend the excitation region of phosphor materials. In addition, the effect of reactional temperature, pH value, and Ca source on the photoluminescence properties was also studied systematically.
- Zhou, Yongqin,Liu, Jie,Yang, Xuyong,Yu, Xibin,Wang, Litong
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- Preparation, characterization and photoluminescence of nanocrystalline calcium molybdate
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Nanocrystalline calcium molybdate was successfully synthesized from Ca(NO3)2 and Na2MoO4 in ethylene glycol using a microwave radiation method. Body-centered tetragonal structured calcium molybdate with narrow n
- Phuruangrat, Anukorn,Thongtem, Titipun,Thongtem, Somchai
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- Structural evolution induced by substitution of designated molybdate sites (MoO4?2) with different anionic groups (BO3?3, PO4?3 and SO4?2) in CaMoO4:Sm3+ phosphors-A study on color tunable luminescent properties
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A series of novel red emitting CaMoO4:Sm3+ (1.0 mol %) phosphors substituted with different anionic groups (BO3?3, PO4?3 and SO4?2) were prepared using a high temperature solid state reaction method. The effects of anionic substitution on the crystalline structure and photoluminescence (PL) properties of the CaMoO4:Sm3+, CaMoO4-BO3:Sm3+, CaMoO4-PO4:Sm3+and CaMoO4-SO4:Sm3+ phosphors were investigated. The structure, particle morphology, chemical composition, vibration modes, and PL properties of the phosphors were investigated by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectrometry (FT-IR) and PL spectroscopy, respectively. The XRD patterns indicated that the crystalline structures of all the samples were consistent with the standard scheelite structure of CaMoO4. The structural parameters of the pure phase of CaMoO4:Sm3+ phosphor were obtained from the Rietveld analysis. Red PL attributed to the 4G5/2 → 6H9/2 transition of Sm3+ was observed at 646 nm when the CaMoO4:Sm3+ samples were excited by 404 nm using a monochromatized Xenon lamp. Furthermore, orange-red color tunable emission has been achieved by substitution of different anionic groups (BO3?3, PO4?3 and SO4?2) into the CaMoO4:Sm3+ phosphors. Among all the studied phosphors, the CaMoO4-SO4:Sm3+ phosphor showed the strongest PL emission compared to all other phosphors suggesting that it is a promising potential candidate for red emission in the near UV excited white LED applications.
- Balakrishna,Swart,Ramaraghavulu,Bedyal,Kroon,Ntwaeaborwa
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- Influence of SO42? anionic group substitution on the enhanced photoluminescence behaviour of red emitting CaMoO4:Eu3+ phosphor
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CaMoO4:xEu3+(x = 0.5, 1.0, 1.5, 2.0, and 2.5) powder phosphors incorporating SO42? anions were synthesized at high temperature using the solid-state reaction technique. The structural, morphological and optical properties of these phosphors were analysed using X-ray diffraction (XRD), field emission scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and optical spectroscopy. The XRD results indicate that the incorporation of SO42? anions and Eu3+ dopant ions did not affect the crystal structure of the CaMoO4, but largely influenced the luminescence properties of the CaMoO4–SO4:Eu3+ phosphors.The optical properties of our materials were examined using the UV–vis absorption spectroscopy. The absorption edges of the phosphors with different concentrations of Eu3+ were less than the band gap energy of the CaMoO4 and their values ranged from 3.30 to 4.75 eV. The intensity of the red photoluminescence (PL) from CaMoO4:Eu3+ phosphors was enhanced considerably upon incorporation of SO42? anions, suggesting that SO42? acted to capture primary excitation energy and transfer it non-radiatively to Eu3+ ions. In addition, the incorporation of SO42? ions also improved the fluorescence decay life-time values of the CaMoO4:xEu3+ phosphors significantly. Tunable emission was observed when the Eu3+ concentration was varied. Our PL results indicated that the CaMoO4–SO4:Eu3+ phosphor exhibited the highest red emission intensity compared to CaMoO4: Eu3+ phosphors, suggesting that CaMoO4–SO4:Eu3+ could be a promising red component material for potential application in white light-emitting diode devices.
- Balakrishna, A.,Letswalo, M. L. A.,Ntwaeaborwa, O. M.,Reddy, L.,Swart, H. C.
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- Lanthanide ions-doped calcium molybdate pie-like microstructures: Synthesis, structure characterization, and luminescent properties
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Lanthanide ions doped CaMoO4with pie-like microstructures were synthesized by a hydrothermal method using phenol-formaldehyde resin (PF) as an inducer. The results of powder X-ray diffraction showed a tetragonal phase of both undoped and Ln3+-doped CaMoO4. The microscopical characterization technology revealed the formation process of the pie-like microparticles. As a morphology inducer, the PF molecules played an important role in the formation of phase structure. The as-obtained materials were characterized using different spectroscopic techniques including FT-IR, Raman spectrum, and PL. The emission color can be easily turned by adjusting the relative doping concentrations of lanthanide ions.
- Han, Yuanyuan,Wang, Liyong,Wang, Dan,Liang, Danyang,Wang, Shiqi,Lu, Guoxin,Di, Zhiyu,Jia, Guang
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- Photoluminescent properties of phosphors in the system Ca xCd1-xMoO4:Eu3+, Li+
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The luminescent properties of the new red phosphors in the solid solution system CaxCd1-xMoO4:Eu3+, Li + are reported. Their dominating emission peaks are at 615 nm, which satisfies color purity. Under the excitation of ~ 320 nm UV light, some selected samples have luminescent intensity 30% higher than that of the commercial red phosphor Y2O2S:Eu3+. Therefore, it is a promising material for N2 plasma display application.
- Wang, Jiaguo,Jing, Xiping,Yan, Chunhua,Lin, Jianhua,Liao, Fuhui
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- Broadly tunable emission from CaMoO4:Bi phosphor based on locally modifying the microenvironment around Bi3+ Ions
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The trivalent green element of bismuth, when doped into different compounds, can produce multiple emissions in ultraviolet, blue, green or even yellow spectral regimes. The emission adjustability comes from the susceptibility of bismuth naked 6s electrons to the crystal field particularly surrounding Bi3+. However, this has never been observed in a single compound. In this work, we report that broadly tunable bismuth emission indeed occurs even within the same host (CaMoO4) when the local microenvironment around Bi3+ is modified by intentional introduction of alkali ions. As the radius of the selected alkali ion decreases, the emission regularly blue-shifts from 586 to 554 nm, and its intensity is enhanced greatly. For instance, the integrated intensity for the Li+ and Bi3+ codoped sample is 4.46 times stronger than the Bi3+ single-doped sample upon excitation at 300 nm. Low-temperature photoluminescence spectra surprisingly reveal that energy transfer can partially take place from the MoO42- group to Bi3+ at lower temperature when excited into the charge transfer state of the MoO42- group, however, this does not occur at higher temperature. The mechanism needs further study. Dynamic luminescence analysis between 10 and 300 K implies a population dependence of the excited states 3P0 and 3P1 on temperature that is responsible for the evolution of the Bi3+ emission lifetime with temperature. Broadly tunable bismuth emission is observed in the host CaMoO4 when the local microenvironment around Bi3+ is modified by alkali ions. Energy transfer can take place from the MoO42- group to Bi 3+ at lower temperature but not at higher temperature. The dependence of the excited states 3P0 and 3P1 on temperature is responsible for the evolution of the Bi3+ emission lifetime with temperature.
- Kang, Fengwen,Peng, Mingying,Xu, Shanhui,Ma, Zhijun,Dong, Guoping,Qiu, Jianrong
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- Structural, lattice vibrational, optical and microwave dielectric studies on Ca1-xSrxMoO4 ceramics with scheelite structure
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Structural, optical and microwave dielectric properties of Ca 1-xSrxMoO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) compositions were studied with help of Rietveld refinement and Raman spectroscopy measurements. All these compositions were prepared by solid state reaction method and observed to possess tetragonal scheelite structure with I41/a space group. Microwave dielectric properties such as dielectric constant (εr), quality factor (Q×f) and temperature coefficient of resonant frequency (τf) were measured using Hakki-Coleman method, reflection technique and invar cavity attached to hot plate respectively. εr, (Q × f) and τf are correlated with molar volume (Vm), MoO bond strength and Raman shift of A1g mode respectively. All these compounds show good microwave dielectric properties (εr = 6.7-9.6, Q × f = 35,000-52,000 GHz and τf = -28 to -17 ppm/°C). Band gap of these compositions was observed in the range 3.3-3.5 eV and variation in band gap was fitted with Bowing equation.
- Ramarao,Kiran, S. Roopas,Murthy
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- Thermal stability of SiO2-B2O3-Al2O3-Na2O-CaO glasses with high Nd2O3 and MoO3 concentrations
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The incorporation of high MoO3 amounts in borosilicate glasses developed for the immobilization of radioactive waste may lead to the crystallization of Mo-rich phases that may induce a decrease of the long term performances of glasses. It is thus essential to understand their crystallization mechanisms and the possible effect of other abundant fission products present in the wastes (such as rare earths) in order to control or to avoid their formation during glass preparation. This paper presents a study, performed by X-ray diffraction, scanning electron microscopy, Raman and optical absorption spectroscopies of the stability as a function of the thermal treatment temperature TC of a simplified Mo-rich nuclear waste glass. The impact of the addition of a high amount of Nd2O3 on the thermal stability of this glass is studied. For comparison, the thermal stability of a Nd2O3-rich glass without Mo is also presented. The crystallization range of all phases formed in these glasses (CaMoO4, Na2MoO4, Ca2Nd8(SiO4)6O2 (apatite)) and the evolution of their structure and microstructure as a function of TC are presented. The introduction of Nd2O3 in the MoO3-rich glass inhibits the crystallization of molybdates (increase of Mo solubility), as long as apatite does not form which suggests that [MoO4]2- entities and Nd3+ cations are close to each other in the glass structure. Besides, when a high density of apatite crystals form, for instance from glass surface, small Mo-rich partially crystallized globular heterogeneities are observed between these crystals that exacerbate the nucleation of new apatite crystals (nucleating effect).
- Chouard, Nolwenn,Caurant, Daniel,Majérus, Odile,Guezi-Hasni, Nadia,Dussossoy, Jean-Luc,Baddour-Hadjean, Rita,Pereira-Ramos, Jean-Pierre
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- High temperature crystal chemistry and thermal expansion of synthetic powellite (CaMoO4): A high temperature X-ray diffraction (HT-XRD) study
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In this communication, the high temperature crystal chemistry of scheelite type (space group: I41/a) CaMoO4 (powellite) is reported. The details of the high temperature crystal structures were obtained by high temperature X-ray diffractometer (HT-XRD) data in the temperature range of 25-1000 °C. The lattice thermal expansions of this compound show the an-isotropic behavior, with the coefficient of thermal expansion along c-axis (αc) is almost double of that along the a-axis (αa). The average values of thermal expansion coefficient for CaMoO4 are: αa=13.5×10-6 and αc=22.8×10-6 °C. The typical thermal expansion behavior is basically controlled by the temperature-induced expansion of the Ca-O bonds, i.e. by the thermal expansion of the CaO8 polyhedra. The MoO4 polyhedra acts as typical rigid unit, with virtually no expansion. The preliminary data analysis for CaWO4 indicates almost similar values of thermal expansion coefficients, viz. αa=12.7×10-6 and αc=21. 4×10-6/°C (for CaWO4) in the same temperature range. The further details are explained in this manuscript.
- Achary,Patwe,Mathews,Tyagi
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- Scheelite-Related Triple Molybdates KCaLn(MoO4)3 in K2MoO4–CaMoO4–Ln2(MoO4)3 (Ln = Nd, Sm, Eu, Gd) Systems: Synthesis and Characterization
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Subsolidus phase ratios in K2MoO4–CaMoO4–Ln2(MoO4)3 systems where Ln = Nd, Sm, Eu, and Gd, have been studied by vibrational spectroscopy, X-ray powder diffraction, and differential thermal analysis. Triple molybdates KCaLn(MoO4)3 (Ln = Nd, Sm, Eu, and Gd) have been synthesized; they have a scheelite-derivative structure, monoclinic crystal system (space group P21/n). Their unit cell parameters have been determined, and IR and Raman spectra characterized.
- Kozhevnikova
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- Fabrication of coupled twin-shaped hollow hemispherical calcium molybdate via a facile ultrasound-assisted approach
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Coupled twin-shaped hollow hemispherical calcium molybdate (CTHH-CaMoO4) microstructures were successfully synthesized via a facile ultrasound-assisted template-free route in the presence of absolute ethanol and ethylenediaminetetraacetic acid (EDTA). The oriented attachment and subsequent Ostwald ripening mechanism were responsible for the formation of this novel architecture. This journal is
- Zhang, Yongfang,Wang, Limin,Chu, Deqing,Sun, Hongming,Wang, Aoxuan,Ma, Zhongchao,Yang, Lufeng,Zhuang, Yan,Bai, Yuze
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- Synthesis and study of ternary molybdates RbCaR(MoO4)3 with a scheelite-like structure in Rb2MoO4–CaMoO4–R2(MoO4)3 systems (R = Nd, Sm, Eu, Gd)
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Phase ratios in the subsolidus regions of Rb2MoO4–CaMoO4–R2(MoO4)3 systems (R = Nd, Sm, Eu, or Gd) were studied by vibrational spectroscopy, X-ray diffraction, and differential thermal analysis. Ternary molybdates RbCaR(MoO4)3 (R = Nd, Sm, Eu, Gd) with scheelite derivative structures (monoclinic symmetry system, space group P21/n) were synthesized. Unit cell parameters were determined, and IR and Raman spectra were characterized.
- Kozhevnikova
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- Thermal annealing effects on the luminescence and scintillation properties of CaMoO4 single crystal grown by Bridgman method
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CaMoO4 single crystal with high quality and large size was grown by Bridgman method. The as-grown CaMoO4 crystal presents blue-black color, and the annealed CaMoO4 crystal presents optically transparent. The mechanisms of crystal fading by thermal annealing were explained in detail. The annealing effects on the optical transmission, photoluminescence spectra, X-ray luminescence spectra and luminescence decay time were investigated. The results indicate that thermal annealing not only has positive effects on reducing oxygen vacancies and alleviating the self-absorption phenomenon, but also the luminescent intensity can be enhanced greatly. The annealed CaMoO4 crystal has moderate Stokes shift (1.46 eV). The light output of annealed CaMoO4 single crystal by the excitation of 662 KeV X-ray from a 137Cs source was measured to be 57.9 p.e. per MeV. This work offers detailed and significant data of scintillation properties of CaMoO4 single crystal, which are very helpful for potential applications in searching for rare events especially in neutrinoless double beta decay area.
- Jiang, Linwen,Wang, Zhenhai,Chen, Hongbing,Chen, Yaping,Chen, Peng,Xu, Zizong
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- Structure-property relationships of novel microwave dielectric ceramics with low sintering temperatures: (Na0.5xBi0.5xCa 1-x)MoO4
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A novel series of microwave dielectric ceramics (Na0.5xBi 0.5xCa1-x)MoO4 (0 ≤ x ≤ 0.6) was synthesized by the solid state reaction method. The crystal structures, microstructures, dielectric responses, and vibrational properties were investigated using X-ray diffraction, scanning electron microscopy, a microwave network analyzer, and terahertz, Raman and infrared spectroscopies. All the samples could be sintered well below 850 °C and a scheelite solid solution could be formed without any secondary phase. At x = 0.5 and x = 0.6, low-firing (750-775 °C) high performance microwave dielectric materials were obtained with permittivities of 19.1-21.9, Q × f values of 20,660-22,700 GHz, and near-zero temperature coefficients. The factors affecting microwave dielectric properties were discussed based on the vibrational data. As revealed by Raman spectroscopy, the disorder degree grows with x rising, which might increase the permittivities and decrease the Q × f values. The infrared spectra were analyzed using the classical harmonic oscillator model, and the complex dielectric responses gained from the fits were extrapolated down to the microwave and THz range. It is believed that the external vibration modes located at low frequencies dominate the main dielectric polarization contributions, especially the Na-O/Bi-O translational mode. This result indicates that the microwave dielectric properties of (Na0.5xBi 0.5xCa1-x)MoO4 ceramics mainly depend on the behavior of AO8 polyhedra. This journal is the Partner Organisations 2014.
- Guo, Jing,Zhou, Di,Li, Yong,Shao, Tao,Qi, Ze-Ming,Jin, Biao-Bing,Wang, Hong
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- Heat capacity and thermodynamic functions of CaMoO4 at low temperatures
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The heat capacity of a single crystal of calcium molybdate CaMoO4 was measured by the adiabatic method in the range 6-310 K. No anomalies in the heat capacity associated with the phase transition were found. Based on the obtained data, thermodynamic functions (entropy, enthalpy, and Gibbs free energy) were calculated. Special features of the heat capacity behavior near zero temperatures as well as special features of the phonon density of states at low frequencies were detected. The low-frequency peak in the phonon density of states of CaMoO4 was identified, which is associated with the phonon scattering on the regular fragments of the structure. The Debye temperature at absolute zero was calculated.
- Musikhin,Naumov,Bespyatov,Shlegel
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- Synthesis and electrical properties of scheelite Ca1-xSm xMoO4+δ solid electrolyte ceramics
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Scheelite-type Ca1-xSmxMoO4+δ electrolyte powders were prepared by the sol-gel auto-combustion process. The crystal structure of the samples was determined by employing the techniques of X-ray diffraction (XRD). According to the XRD analysis, the formed continuous series of Ca1-xSmxMoO4+δ (0 ≤ x ≤ 0.3) solid solutions had the structure of tetragonal scheelite, and the lattice parameters increased with increasing x in the Sm-substituted system. Results of sinterability and electrochemical testing revealed that the performances of Sm-doped calcium molybdate were superior to that of pure CaMoO4. Ca1-xSmxMoO4+δ ceramics show higher sinterability, and the Ca0.8Sm0.2MoO4+δ sample with 98.7% of the theoretical density were obtained after being sintered at 1250 °C for 4 h. The conductivity increased with increasing samarium content, and a total conductivity 9.54 × 10-3 S cm-1 at 800 °C could be obtained in Ca0.8Sm0.2MoO 4+δ sintered at 1250 °C for 4 h.
- Cheng, Jihai,Liu, Chenfei,Cao, Wenbing,Qi, Mingxing,Shao, Guoquan
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- Ca1-2xEuxLixMoO4: A novel red phosphor for solid-state lighting based on a GaN LED
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A novel red phosphor Ca1-2xEuxLixMoO 4 with high performance is reported. Under the excitation of 254 run UV light, its luminescent intensity is comparable to that of the commercial red phosphor Y2O3:Eu3+. With high Eu3+ concentration, the phosphor has strong excitation due to f-f transitions of Eu3+ appearing around 395 nm. Thus, it is a promising material for solid-state lighting based on GaN light-emitting diode (LED).
- Wang, Jiaguo,Jing, Xiping,Yan, Chunhua,Lin, Jianhua
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- Microwave dielectric properties of the (1?x)La(Nb0.9V0.1)O4-xCaMoO4 (0.05?≤?x?≤?0.50) scheelite solid solution ceramics
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The CaMoO4 was added into La(Nb0.9V0.1)O4 ceramics by solid state reaction method to adjust the temperature coefficient of frequency (TCF) values. The series of (1?x)La(Nb0.9V0.1)O4-xCaMoO4 (0.05 ≤ x ≤ 0.5) ceramics were sintered at 1060–1180 °C and found to possess permittivity (εr) = 10.38–17.73, Q × f = 31,820–76,570 GHz (Q = 1/dielectric loss, f = resonant frequency lying between 8.5 and 9 GHz), and TCF = ?26.3 ~ +160.7 ppm/°C. The structures of ceramic samples changed from monoclinic fergusonite to tetragonal scheelite continuously at x = 0.20 along with the shift of TCF values from positive to negative. The best microwave dielectric properties with εr = 15.71, Q × f = 76,310 GHz (at 8.825 GHz), and TCF = ? 26.3 ppm/°C were obtained in 0.8La(Nb0.9V0.1)O4-0.2CaMoO4 ceramics sintered at 1160 °C and these ceramics might be good candidates for microwave devices.
- Ma, Zhili,Zhao, Jinxiong,Zhou, Di
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- Synthesis, structure and vibration spectra of the triple molybdates Tl5A0.5Hf1.5(MoO4)6, A = Ca, Sr, Ba, Pb
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The systems Tl2MoO4-AMoO4-Hf(MoO4)2 (A = Ca, Sr, Ba, Pb) have been studied in their subsolidus regions using X-ray powder diffraction and differential thermal analysis. Intermediate phases of composition 5:1:3 are formed in these systems. The crystallographic and thermal characteristics of these phases have been determined. The vibration spectra of Tl5A0.5Hf1.5(MoO4)6 (A = Ca, Sr, Ba, Pb) have been considered and analysed for each new compound. In the Raman spectra, the influence of the divalent cation on the bands of the ν1 vibrational mode and deformation fluctuations has been demonstrated. The bands of the ν3(F2) vibrational mode are split in the IR spectra of the given triple molybdates. This splitting increases with the radius of the divalent cation.
- Bazarov,Sarapulova,Klevtsova,Glinskaya,Fedorov,Bazarova
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- LUMINESCENCE OF CALCIUM MOLYBDATE.
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Two emission bands are observed, one in the green and another in the orange spectral region. The shorter wavelength emission band is assigned to the **3T//1 yields **1A//1 transition in the tetrahedral molybdate group. The longer wavelength band is ascribed to a similar transition in a molybdate group lacking an oxygen ion, i. e. a MoO//3 group. Similar observations are made in the case of calcium tungstate.
- Groenink,Hakfoort,Blasse
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- Manometric real-time studies of the mechanochemical synthesis of zeolitic imidazolate frameworks
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We demonstrate a simple method for real-time monitoring of mechanochemical synthesis of metal-organic frameworks, by measuring changes in pressure of gas produced in the reaction. Using this manometric method to monitor the mechanosynthesis of the zeolitic imidazolate framework ZIF-8 from basic zinc carbonate reveals an intriguing feedback mechanism in which the initially formed ZIF-8 reacts with the CO2 byproduct to produce a complex metal carbonate phase, the structure of which is determined directly from powder X-ray diffraction data. We also show that the formation of the carbonate phase may be prevented by addition of excess ligand. The excess ligand can subsequently be removed by sublimation, and reused. This enables not only the synthesis but also the purification, as well as the activation of the MOF to be performed entirely without solvent.
- Brekalo, Ivana,Yuan, Wenbing,Mottillo, Cristina,Lu, Yuneng,Zhang, Yuancheng,Casaban, Jose,Holman, K. Travis,James, Stuart L.,Duarte, Frédéric,Williams, P. Andrew,Harris, Kenneth D. M.,Fri??i?, Tomislav
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- Excitation spectra and luminescence decay analysis of K+ compensated Dy3+ doped CaMoO4 phosphors
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A series of Dy3+/K+ doped calcium molybdate phosphors were synthesized by a hydrothermal synthesis method and structural, photoluminescence and decay studies were carried out. The crystal structure and phase of the prepared phosphors were investigated using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). These studies show that the phosphors are of a tetragonal structure with a nanorod morphology. The photoluminescence results indicate that these phosphors could be efficiently excited by near-ultraviolet radiation which causes emission in the blue and yellow regions. A novel approach was used to calculate different spectral parameters of powder samples using excitation spectra instead of conventional absorption spectra. Quantitative calculation of spectral parameters, luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting devices.
- Dutta,Som,Sharma
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- Immobilization of mo6+ in monazite lattice: Synthesis and characterization of new phosphomolybdates, La1-xCa xP1-yMoyO4, Where x=y=0.1-0.9
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In the process of high-level nuclear waste (HLW) disposal, monazite, LaPO4 is considered as one of the potential phosphate ceramics to immobilize lanthanides and actinides. HLW along with hazardous long-lived nuclides contains elements such as Zr, Mo, etc. in higher wt%. In the current investigation, an attempt was made to introduce Mo into the monazite lattice. The phosphomolybdates of the formula La1-xCa xP1-yMoyO4, x, y=0.1-0.9 were synthesized by a solution route and characterized by powder X-ray diffraction, FT-IR, TGA/DTA, and scanning electron microscopic techniques. The phases with compositions La0.9Ca0.1P0.9Mo 0.1O4, La0.8Ca0.2P 0.8Mo0.2O4, and La0.7Ca 0.3P0.7Mo0.3O4 were found to be crystallized in monazite structure. The composition La0.1Ca 0.9P0.1Mo0.9O4 with X=Y=0.9 crystallized in the scheelite structure. The compositions indicate the immobilization of a4.1, 8.5, 12.9, and 42.5 at. wt% of Mo. With x, y=0.6, 0.5, 0.4, 0.3, and 0.2, along with the monazite phase, formation of a secondary phase LaP3O9 was observed.
- Kumar, Sathasivam Pratheep,Gopal, Buvaneswari
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- The disordered cluster compound CaMo5(Mo0.38Ti 0.62)O10
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The title compound, calcium penta-molybdenum titanium deca-oxide, is isomorphous with the AMo5(Ti0.7Mo0.3)O10 (A = Sr and Eu) compounds. The smaller size of calcium induces a higher molybdenum content on the capping sites of the bioctahedral Mo10 clusters, leading to more Mo11 and Mo12 clusters in the crystal structure. The oxygen framework derives from the stacking of close-packed layers along the a direction in the ABAC sequence. The Ca 2+ ions occupy large cavities which result from the fusion of two cubo-octahedra and are surrounded by ten O atoms. The Ti4+ ion is octa-hedrally coordinated by the O atoms.
- Gougeon,Gall
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- Synthesis, sintering and optical properties of CaMoO4: A promising scheelite LTCC and photoluminescent material
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The synthesis of nanocrystalline calcium molybdate (CaMoO4) through an autoigniting combustion technique is reported in this paper. The structural characterization of the as-prepared nanocrystallites were done by X-ray diffraction (XRD), Fourier transform Raman, and Fourier transform infrared (IR) spectroscopy and the morphological studies using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The studies reveal that the as-prepared powder itself was phase pure with tetragonal structure and of particle size 25 nm. The sample was sintered at a relatively low temperature of 775 °C to a high density of ~95% for the first time, without the use of any sintering aid. The optical bandgap energy calculated from the ultraviolet-visible absorption spectrum for the as-prepared and annealed sample was 3.72 and 3.99 eV, respectively. The photoluminescence spectra of the sample showed an intense emission in the green region (528 nm). The dielectric constant and loss factor of the sample at 5 MHz was found to be 11.00 and 6.40 × 10-3 at room temperature. The temperature coefficient of dielectric constant was -95.04 pp/°C. These observations reveal that nanostructured CaMoO4 is a promising scheelite low-temperature co-fired ceramic (LTCC) and also an excellent luminescent material. Copyright
- Vidya,Solomon,Thomas
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- Luminescence and photometric characterization of K+ compensated CaMoO4:Dy3+ nanophosphors
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A series of CaMoO4 phosphors doped with trivalent dysprosium (Dy3+) and codoped with potassium (K+) ions were prepared by hydrothermal method. The nanostructures of the as-synthesized phosphors were investigated by X-ray diffraction (XRD). The results reveal that the obtained powder phosphors are single-phase scheelite structure with tetragonal symmetry and the crystallite size is in the range of 10-60 nm. The emission spectra show a bright yellow emission at 576 nm and blue emission at 487 nm. As a charge compensator, K+ ions were incorporated into CaMoO4:Dy 3+ phosphors, which enhance the PL intensities depending on the doping concentration of K+. The CIE parameters such as colour coordinates, colour correlated temperature and luminous efficacy of radiation were calculated using spectral energy distribution functions and McCamy's empirical formula. Photometric characterization indicates the suitability of K+ compensated CaMoO4:Dy3+ phosphor for white LED applications. The Royal Society of Chemistry 2013.
- Dutta,Som,Sharma
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Read Online
- Realization of neutral white light emission in CaMoO4:4Dy3+ phosphor via Sm3+co-doping
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In this paper, Dy3+/Sm3+ co-doped CaMoO4 compounds were synthesized successfully via the auto-combustion method. The tetragonal crystal structure of the phosphors is confirmed by structural study. The vibrational modes are
- Chauhan, Vaibhav,Dixit, Prashant,Pandey, Praveen C.,Rai, S. B.
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- Traditional salt-in-water electrolyte: Vs. water-in-salt electrolyte with binary metal oxide for symmetric supercapacitors: Capacitive vs. faradaic
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The electrochemical energy storage of lithium and sodium ions from aqueous solutions in binary metal oxides is of great interest for renewable energy storage applications. Binary metal oxides are of interest for aqueous energy storage due to their better structural stability and electronic conductivity and tunability of redox potentials. They have also been widely studied as novel electrodes for supercapacitors. The interactions between water and lithium/sodium ions, and water and binary metal oxide surface determine the electrochemical reactions and their long-term stability. Our results indicate that the aqueous sodium electrolyte has a stronger influence on the capacitance and cycling stability of the binary (Ca and Mo) metal oxide electrode than its lithium cousin. The symmetric cell in a two-electrode configuration was assembled with the proposed binary metal oxide, which shows an average discharge voltage of 1.2 V, delivering a specific capacitance of 72 F g-1 at a specific energy density of 32 W h kg-1 based on the total mass of the active materials. The development of highly concentrated aqueous electrolytes such as the water-in-salt electrolyte showed a larger electrochemical (voltage) window with enhanced storage capacitance for increasing the salt concentrations has also been discussed.
- Appadoo, Dominique,Sundaram, Manickam Minakshi
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p. 11743 - 11755
(2020/09/09)
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- Scheelite-related M II: X Bi1- xV1- xMoxO4 (MII-Ca, Sr) solid solution-based photoanodes for enhanced photoelectrochemical water oxidation
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The photoelectrochemical properties of scheelite-related MIIxBi1-xV1-xMoxO4 (MII = Ca, Sr, x = 0.1 to 0.9) solid solutions deposited on conductive glass (coated with SnO2, F-doped) have been investigated as photoanodes in photoelectrochemical (PEC) water splitting. The variation of the final annealing temperature during the preparation of the conduction electrodes as well as the value of substitution x have been shown to affect the PEC performance. The micropowders of MIIxBi1-xV1-xMoxO4 (MII = Ca, Sr, x = 0.1 to 0.9) samples were first fabricated vi a solid-state method; they were characterised by SEM microscopy and powder and single crystal X-ray diffraction, and the band gap values were estimated using diffusive reflectance data. The value of substitution x = 0.1 in the cases of samples containing calcium and strontium affords the highest PEC performance reported for the whole range of substitution. These results demonstrate a promising approach for the beneficial utilization of BiVO4-substituted scheelite-related solid solutions in photo-electrochemical cells towards efficient and inexpensive photoanodes.
- Li, Shilin,Bychkov, Konstantin L.,Butenko, Denys S.,Terebilenko, Kateryna V.,Zhu, Yukun,Han, Wei,Baumer, Vyacheslav N.,Slobodyanik, Mykola S.,Ji, Hong,Klyui
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p. 2345 - 2355
(2020/02/26)
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- Synthesis and luminescence properties of a Li3BaCaY3(MoO4)8:Er3+ phosphor with a layered scheelite-like structure
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A Li3BaCaY3(MoO4)8:Er3+ phosphor with a scheelite-like structure (sp. gr. C2/c) has been synthesized and its luminescence properties have been studied. The phosphor has been characterized by X-ray dif
- Kozhevnikova
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p. 419 - 423
(2017/04/06)
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- Incorporation of Europium(III) into Scheelite-Related Host Matrixes ABO4 (A = Ca2+, Sr2+, Ba2+ B = W6+, Mo6+): Role of A and B Sites on the Dopant Site Distribution and Photoluminescence
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Scheelite- and powellite-related materials doped with trivalent lanthanides or actinides have been the subject of extensive research due to their important role in mineralogical, technological, and environmental implications. Detailed structural knowledge of these solid solutions is essential for understanding their physicochemical properties and predicting material properties. In this work, we conduct a comprehensive spectroscopic analysis by means of polarization-dependent site-selective time-resolved laser-induced fluorescence spectroscopy, to delineate the influence of the host phase cations for a series of scheelite-type matrixes based on a general formula of ABO4 (A = Ca2+, Sr2+, Ba2+ B = W6+, Mo6+) on the local environment of the Eu3+ dopant. Eu3+ has been used as a luminescent probe to access the local structural environment of crystalline substitutional sites suitable for trivalent lanthanide or actinide occupation. Our results show that the lattice distortion is overall minor, but increases with increasing mismatch of host and guest cation size. We observe a linear dependence of Eu3+'s excitation energy on the host cation size and the A-O bond distance, which can be used to determine the hitherto unknown Eu-O bond distance in NaEu(WO4)2. A value of 2.510 ? was determined, somewhat larger than a previously reported number for NaEu(MoO4)2. The results also show clear evidence that the local coordination environment of Eu3+ in WO42- materials is more symmetrical than in their isostructural MoO42- counterparts. The detailed spectroscopic interpretation conducted in this study resolves the relation between local distortion around a dopant and the host phase cations in structural disordered materials and may give novel insights with respect to rational design and tailoring of functional materials.
- Xiao, Bin,Schmidt, Moritz
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p. 14948 - 14959
(2017/12/26)
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- Electrical conductivity and thermal expansion behavior of MMoO4 (M = Ca, Sr and Ba)
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Abstract Alkaline earth (Ca, Sr, Ba) molybdates were synthesized by solid state reaction route. The compounds were characterized by powder-XRD, TG-DTA techniques. The electrical conductivities of these compounds were measured by AC-impedance technique at
- Maji, Binoy Kumar,Jena, Hrudananda,Asuvathraman,Kutty, K.V. Govindan
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p. 475 - 479
(2015/04/27)
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- Energy transfer dynamics and luminescence properties of Eu3+ in CaMoO4 and SrMoO4
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Undoped and europium doped CaMoO4 and SrMoO4 scheelites are synthesized using a complex polymerization method. The phase purity of the sample is confirmed using powder X-ray diffraction (PXRD). X-ray photoelectron spectroscopy (XPS) was carried out to confirm the oxidation states of various constituents and dopant elements and also the presence of oxygen vacancies. Interestingly both CaMoO4 and SrMoO4 on irradiation with UV light give blue and green emission respectively. On europium doping, it was found that molybdate to Eu3+ ion energy transfer is more efficient in SrMoO4:Eu compared to CaMoO4:Eu. It is also justified using a luminescence lifetime study which shows biexponential decay in the case of CaMoO4:Eu corresponding to both the host and europium ion; whereas a single lifetime is observed in the case of SrMoO4:Eu. Anomalies in host-dopant energy transfer are suitably explained using density functional theory (DFT) calculations and XPS. The actual site symmetry for the europium ion in CaMoO4 and SrMoO4 was also evaluated based on a Stark splitting pattern which turns out to be D2 and C2v respectively although it is S4 for Ca/Ba2+ in AMoO4. This is also reflected in higher Ω2 values for SrMoO4:Eu than CaMoO4:Eu.
- Gupta, Santosh K.,Sahu,Ghosh,Tyagi, Deepak,Saxena,Kadam
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p. 18957 - 18969
(2015/11/11)
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- Aqueous sol-gel synthesis and thermoanalytical study of the alkaline earth molybdate precursors
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The preparation and characterization of the M-Mo-O nitrate-tartrate (M = Mg, Ca, Sr, and Ba) gels, which were produced by the simple aqueous sol-gel method and calcined at 500, 600, 700, 800, 900, and 1,000 °C temperatures are reported. The crystalline al
- Braziulis, Gediminas,Janulevicius, Gytautas,Stankeviciute, Ruta,Zalga, Arturas
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p. 613 - 621
(2015/01/09)
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- Microstructure and spectroscopic properties of AMoO4 (A = Ca, Ba) particles synthesized via cyclic microwave-assisted metathetic route
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AMoO4 (A=Ca, Ba) particles have been successfully synthesized via cyclic microwave-assisted metathetic route in ethylene glycol followed by further heat-treatment. The AMoO4 (A=Ca, Ba) particles were well crystallized after heat-treatment at 400-600 °C for 3 h. The microstructures exhibited fine morphologies with sizes of 0.5-1 and 1.5-2 μm for the CaMoO4 and BaMoO4 particles, respectively. The synthesized AMoO4 (A=Ca, Ba) particles were characterized by X-ray diffraction, scanning electron microscopy. Other spectroscopic properties were also examined using photoluminescence emission measurements and Raman spectroscopy.
- Lim, Chang Sung
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p. 1865 - 1868
(2014/06/09)
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- Broadly tunable emission from CaMoO4:Bi phosphor based on locally modifying the microenvironment around bi3+ ions
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The trivalent green element of bismuth, when doped into different compounds, can produce multiple emissions in ultraviolet, blue, green or even yellow spectral regimes. The emission adjustability comes from the susceptibility of bismuth naked 6s electrons to the crystal field particularly surrounding Bi3+. However, this has never been observed in a single compound. In this work, we report that broadly tunable bismuth emission indeed occurs even within the same host (CaMoO4) when the local microenvironment around Bi3+ is modified by intentional introduction of alkali ions. As the radius of the selected alkali ion decreases, the emission regularly blue-shifts from 586 to 554 nm, and its intensity is enhanced greatly. For instance, the integrated intensity for the Li+ and Bi3+ codoped sample is 4.46 times stronger than the Bi3+ single-doped sample upon excitation at 300 nm. Low-temperature photoluminescence spectra surprisingly reveal that energy transfer can partially take place from the MoO42- group to Bi3+ at lower temperature when excited into the charge transfer state of the MoO42- group, however, this does not occur at higher temperature. The mechanism needs further study. Dynamic luminescence analysis between 10 and 300 K implies a population dependence of the excited states 3P0 and 3P1 on temperature that is responsible for the evolution of the Bi3+ emission lifetime with temperature. Broadly tunable bismuth emission is observed in the host CaMoO4 when the local microenvironment around Bi3+ is modified by alkali ions. Energy transfer can take place from the MoO42- group to Bi3+ at lower temperature but not at higher temperature. The dependence of the excited states 3P0 and 3P1 on temperature is responsible for the evolution of the Bi3+ emission lifetime with temperature.
- Kang, Fengwen,Peng, Mingying,Xu, Shanhui,Ma, Zhijun,Dong, Guoping,Qiu, Jianrong
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p. 1373 - 1380
(2015/04/27)
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- Single phase melt processed powellite (Ba,Ca)MoO4 for the immobilization of Mo-rich nuclear waste
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Crystalline and glass composite materials are currently being investigated for the immobilization of combined High Level Waste (HLW) streams resulting from potential commercial fuel reprocessing scenarios. Several of these potential waste streams contain elevated levels of transition metal elements such as molybdenum (Mo). Molybdenum has limited solubility in typical silicate glasses used for nuclear waste immobilization. Under certain chemical and controlled cooling conditions, a powellite (Ba,Ca)MoO4 crystalline structure can be formed by reaction with alkaline earth elements. In this study, single phase BaMoO4 and CaMoO4 were formed from carbonate and oxide precursors demonstrating the viability of Mo incorporation into glass, crystalline or glass composite materials by a melt and crystallization process. X-ray diffraction, photoluminescence, and Raman spectroscopy indicated a long range ordered crystalline structure. In situ electron irradiation studies indicated that both CaMoO4 and BaMoO4 powellite phases exhibit radiation stability up to 1000 years at anticipated doses with a crystalline to amorphous transition observed after 1 × 1013 Gy. Aqueous durability determined from product consistency tests (PCT) showed low normalized release rates for Ba, Ca, and Mo (2).
- Brinkman, Kyle,Fox, Kevin,Marra, James,Reppert, Jason,Crum, Jarrod,Tang, Ming
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p. 136 - 142
(2013/03/13)
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- Phase formation in Li2MoO4-K2MoO 4-MMoO4 (M = Ca, Pb, Ba) systems and the crystal structure of α-KLiMoO4
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Solid-phase interactions in Li2MoO4-K 2MoO4-MMoO4 (M = Ca, Pb, Ba) systems were studied, and the subsolidus regions of these systems were triangulated. The lead and barium systems were studied in a more detailed way to discover that, along KLiMoO4-K2M(MoO4)2 (M = Pb, Ba), KLiMoO4-PbMoO4, and Li2MoO4-K 2Ba(MoO4)2 quasi-binary sections, there are homogeneity regions reaching 6-11 mol % based on K2M(MoO 4)2 and lead molybdate. Triple molybdates are formed in none of the systems, which is verified by experiments on spontaneous crystallization from solution in melt. Crystallization experiments yielded crystals of potassium dimolybdate and simple and double molybdates from the boundary systems. The crystal structure was solved for a hexagonal KLiMoO 4 phase: (Na,K){ZnPO4}, a = 18.8838(7) ?, c = 8.9911(6)?, Z = 24, space group P63, R = 0.065. The structure comprises a three-dimensional tridymite framework built by an alternation of corner-sharing LiO4- and MoO4 tetrahedra wherein voids are occupied by potassium cations.
- Gudkova,Solodovnikova,Solodovnikov,Zolotova,Kurat'Eva
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p. 1443 - 1452
(2011/12/13)
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- Phase formation, structural and microstructural characterization of novel oxynitride-perovskites synthesized by thermal ammonolysis of (Ca,Ba)MoO4 and (Ca,Ba)MoO3
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Reactions of AMoO4 and AMoO3 (A=Ca2+, Ba2+) with ammonia were investigated at 873 K3 and to study their crystal structure. CaMo(O,N)3 and BaMo(O,N)3 were prepared by thermal ammonolysis of the corresponding CaMoO3 and BaMoO3 precursors at T=898 and 998 K, respectively. The structural parameters of the oxynitrides were obtained from Rietveld refinements of X-ray and neutron powder diffraction data. CaMo(O,N)3 crystallizes in the GdFeO3 distorted perovskite structure with orthorhombic space group Pbnm and a=5.5029(1) A, b=5.5546(1) A, c=7.8248(1) A as determined by X-ray powder diffraction. Its O/N content refined from the neutron diffraction data corresponds to the composition CaMoO1.7(1)N1.3(1). BaMo(O,N)3 crystallizes in the cubic perovskite structure with space group Pm3m and a=4.0657(1) A as determined by X-ray powder diffraction. Transmission electron microscopy reveals a complex microstructure for both CaMoO3 and CaMoO1.7(1)N1.3(1) represented by twin domains of different orientation.
- Logvinovich,Aguirre,Hejtmanek,Aguiar,Ebbinghaus,Reller,Weidenkaff
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p. 2243 - 2249
(2009/06/05)
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- Phase formation in the systems K2MoO4-AMoO 4-Hf(MoO4)2 (A = Ca, Sr, Ba, Pb)
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The systems K2MoO4-AMoO4-Hf(MoO 4)2 (A = Ca, Sr, Ba, Pb) have been studied in their subsolidus regions using X-ray powder diffraction and differential thermal analysis. Intermediate phases of composition 5 : 1 : 3 are formed in the systems. The crystallographic and thermal characteristics of these phases have been determined. Copyright
- Bazarov,Sarapulova,Bazarova, Zh.G.
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p. 1266 - 1269
(2008/10/09)
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- Synthesis of molybdates of alkaline-earth metals
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A combined method of physicochemical analysis was used to show the possibility of synthesizing molybdates of alkaline-earth metals by exchange reactions in ternary mutual systems.
- Dibirov,Gasanaliev
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p. 1498 - 1501
(2007/10/03)
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