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1.
Two different cerium(IV) phosphates have been prepared by ageing at 95 °C an aqueous solution made from Ce(NO3)6(NH4)2, nitric acid, and phosphoric acid with the following conditions: P/Ce=2, [HNO3]=5.8 M and [Ce4+]=0.1 M. The control over the formed solid was achieved through the ageing time. After 18 h, a metastable compound (A), corresponding to Ce(PO4)1.5(H2O)(H3O)0.5(H2O)0.5, is obtained, while after 5 days a stable one (B), corresponding to Ce(PO4)(HPO4)0.5(H2O)0.5, is recovered. Both solids exhibit a P/Ce ratio of 1.5. Their structures, 31P solid state NMR, and thermal behaviors are compared.  相似文献   

2.
Photoluminescence of compounds that contain stoichiometric zirconium has been studied under vacuum ultraviolet excitation. The compounds show emission peaking at 280-320 nm while the excitation spectra show some bands in 130-190 nm region. The ultraviolet emission is explained as Zr to O charge transfer transition. The luminescence result and structural information classify the studied compounds into two groups. The former group involves ZrP2O7, CaZr(PO4)2, NaZr2(PO4)3, Ca2ZrSi4O12, Ca3ZrSi2O9 and SrZrSi2O7, which show rather intense luminescence and do not have any infinite Zr-O-Zr-O-3D chain or link in their structure. The latter group is CaZrO3 and ZrSiO4, which do contain infinite Zr-O-Zr-O-3D chain and show quite weak luminescence. Luminescence of Ca1−xMnxZr(PO4)2 has also been studied. By replacing a part of Ca with Mn, ultraviolet emission of the host weakens and visible emission peaking at 540 nm appears. It is claimed that transfer of absorbed energy from Zr to Mn occurs.  相似文献   

3.
The redox reaction of Ce4+-Ce3+ promoted by the catalytic function of nickel ions in a (1−x)CeO2-xNiO solid solution was investigated for solar H2 production by the two-step water-splitting reaction. By irradiation using an infrared imaging lamp as a solar simulator, the O2-releasing reaction with (1−x)CeO2-xNiO solid solution proceeded at 1673-1873 K, and its reduced form was produced. The amounts of H2 gas evolved by the reduced form were 1.2-2.5 cm3/g and the evolved gases amounts ratio of H2/O2 was nearly 2, which is equal to the stoichiometric value of the water-splitting reaction (H2O=H2+1/2O2). The maximum amounts of evolved H2 and O2 gases were obtained at the Ce:Ni mole ratio of 0.95:0.05 (x=0.05) in the (1−x)CeO2-xNiO system. The X-ray absorption fine structure (XAFS) measurement showed that the O2-releasing and H2-generation reactions with (1−x)CeO2-xNiO solid solution were repeatable with the redox system of Ce4+-Ce3+, which was enhanced by the catalytic function of Ni2+-Ni0.  相似文献   

4.
Hydroxyapatite (HAp) films were deposited by electron cyclotron resonance plasma sputtering under a simultaneous flow of H2O vapor gas. Crystallization during sputter-deposition at elevated temperatures and solid-phase crystallization of amorphous films were compared in terms of film properties. When HAp films were deposited with Ar sputtering gas at temperatures above 460 °C, CaO byproducts precipitated with HAp crystallites. Using Xe instead of Ar resolved the compositional problem, yielding a single HAp phase. Preferentially c-axis-oriented HAp films were obtained at substrate temperatures between 460 and 500 °C and H2O pressures higher than 1×10−2 Pa. The absorption signal of the asymmetric stretching mode of the PO43− unit (ν3) in the Fourier-transform infrared absorption (FT-IR) spectra was the narrowest for films as-crystallized during deposition with Xe, but widest for solid-phase crystallized films. While the symmetric stretching mode of PO43− (ν1) is theoretically IR-inactive, this signal emerged in the FT-IR spectra of solid-phase crystallized films, but was absent for as-crystallized films, indicating superior crystallinity for the latter. The Raman scattering signal corresponding to ν1 PO43− sensitively reflected this crystallinity. The surface hardness of as-crystallized films evaluated by a pencil hardness test was higher than that of solid-phase crystallized films.  相似文献   

5.
《Solid State Ionics》1988,26(3):203-207
The conductivity of calcium phosphates has been found related to the simultaneous presence of P-OH functions and hydration water. Thus at 200–300°C in 5 atm flowing steam the conductivities of Ca(H2PO4)2·H2O and CaHPO4·2H2O are > 10−3 ω−1 cm−1. Both the anhydrous acid hydrogen phosphates, CaHPO4 and Ca2HP3O10, and the neutral phosphates, Ca2P2O7, Ca(PO3)2 and Ca3(PO4)2, have lower conductivities.  相似文献   

6.
ABSTRACT

Raman spectra of the uranyl-containing mineral coconinoite, Fe2Al2(UO2)2(PO4)4(SO4)(OH)2 · 20H2O, are presented and compared with the mineral's infrared spectra. Bands connected with (UO2)2+, (PO4)3?, (SO4)2?, (OH)?, and H2O stretching and bending vibrations are assigned. Approximate U?O bond lengths in uranyl, (UO2)2+, and O?H…O hydrogen bond lengths are calculated from the wavenumbers of the U?O stretching vibrations and (OH)? and H2O stretching vibrations, respectively, and compared with published data for similar natural and synthetic compounds.  相似文献   

7.
α-Fe2O3-In2O3 mixed oxide nanoparticles system has been synthesized by hydrothermal supercritical and postannealing route, starting with (1−x)Fe(NO3)3·9H2xIn(NO3)3·5H2O aqueous solution (x=0-1). X-ray diffraction and Mössbauer spectroscopy have been used to study the phase structure and substitutions in the nanosized samples. The concentration regions for the existence of the solid solutions in the α-Fe2O3-In2O3 nanoparticle system together with the solubility limits of In3+ ions in the hematite lattice and of Fe3+ ions in the cubic In2O3 structure have been evidenced. In general, the substitution level is considerably lower than the nominal concentration x. A justification of the processes leading to the formation of iron and indium phases in the investigated supercritical hydrothermal system has been given.  相似文献   

8.
Luminescent properties of manganese(II) phosphates prepared by thermal dehydration of Mn(H2PO4)2·2H2O have been studied. The emission spectrum consists of two bands whose relative intensity and spectral position depend on the chemical and crystalline structure of phosphates. The different courses of temperature quenching of luminescence intensity and excitation spectra of each emission band of Mn(H2PO4)2·2H2O, Mn(H2PO4)2, MnH2P2O7 and c-Mn2P4O12 are discussed.  相似文献   

9.
Lead containing calcium zinc sodium fluoroborate (LCZSFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. The experimentally determined oscillator strengths have been determined by measuring the areas under the absorption peaks and the Judd–Ofelt (J–O) intensity parameters were calculated using the least squares fit method. From the evaluated J–O parameters the radiative transition probability rates, radiative lifetimes and branching ratios were calculated for 4F9/2 excited level. Room temperature photoluminescence spectra for different concentrations of Dy3+-doped LCZSFB glasses were obtained by exciting the glass samples at 386 nm. The intensity of Dy3+ emission spectra increases with increasing concentration of 0.1, 0.25, 0.5 and 1.0 mol% and beyond 1.0 mol% the concentration quenching is observed. The measuring branching ratios are reasonably high for transitions 4F9/26H15/2 and 6H13/2, suggesting that the emission at 484 and 576 nm, respectively, can give rise to lasing action in the visible region. From the visible emission spectra, yellow–blue (Y/B) intensity ratios and chromaticity color coordinates were also estimated. The lifetimes of 4F9/2 metastable state for the samples with different concentrations were also measured and discussed.  相似文献   

10.
Zinc blende (ZB) CdSe hollow nanospheres were solvothermally synthesized from the reaction of Cd(NO3)2·4H2O with a homogeneously secondary Se source, which was first prepared by dissolving Se powder in the mixture of ethanol and oleic acid at 205 °C. As Se power directly reacted with Cd(NO3)2·4H2O in the above mixed solvents, wurtzite (W) CdSe solid nanoparticles were produced. Time-dependent experiments suggested that the formation of CdSe hollow nanospheres was attributed to an inside-out Ostwald ripening process. The influences of reaction time, temperature and ethanol/oleic acid volume ratio on the morphology, phase and size of the hollow nanospheres were also studied. Infrared (IR) spectroscopy investigations revealed that oleic acid with long alkene chains behaved as a reducing agent to reduce Se powder to Se2− in the synthesis. Photoluminescence (PL) measurements showed that the ZB CdSe hollow nanospheres presented an obvious blue-shifted emission by 42 nm, and the W CdSe solid nanoparticles exhibited a band gap emission of bulk counterpart.  相似文献   

11.
The minerals of the mixite group—zálesíite CaCu6[(AsO4)2(AsO3OH)(OH)6]·3H2O from abandoned uranium deposit Zálesí, Czech Republic and calciopetersite CaCu6[(PO4)2(PO3OH)(OH)6]·3H2O from a quarry near Domašov na Bystřicí, northern Moravia, Czech Republic—were studied by Raman and infrared spectroscopy. The observed bands were assigned to the stretching and bending vibrations of (AsO4)3− and (AsO3OH)2− ions in zálesíite, and (PO4)3− and (PO3OH)2− in calciopetersite, and to molecular water, hydroxyl ions, and Cu‐(O,OH) units in both minerals. O H···O hydrogen‐bond lengths in zálesíite and calciopetersite structures were calculated with Libowitzky's empirical relation. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

12.
A new compound, K4(SO4)(HSO4)2(H3AsO4) was synthesized from water solution of KHSO4/K3H(SO4)2/H3AsO4. This compound crystallizes in the triclinic system with space group P1¯ and cell parameters: a=8.9076(2) Å, b=10.1258(2) Å, c=10.6785(3) Å; α=72.5250(14)°, β=66.3990(13)°, γ=65.5159(13)°, V=792.74(3) Å3, Z=2 and ρcal=2.466 g cm−3. The refinement of 3760 observed reflections (I>2σ(I)) leads to R1=0.0394 and wR2=0.0755. The structure is characterized by SO42−, HSO4 and H3AsO4 tetrahedra connected by hydrogen bridge to form two types of dimer (H(16)S(3)O4?S(1)O42− and H(12)S(2)O4?H3AsO4). These dimers are interconnected along the [1¯ 1 0] direction by the hydrogen bonds O(3)-H(3)?O(6). They are also linked by the hydrogen bridge assured by the hydrogen atoms H(2), H(3) and H(4) of the H3AsO4 group to build the chain S(1)O4?H3AsO4 which are parallel to the “a” direction. The potassium cations are coordinated by eight oxygen atoms with K-O distance ranging from 2.678(2) to 3.354(2) Å.Crystals of K4(SO4)(HSO4)2(H3AsO4) undergo one endothermic peak at 436 K. This transition detected by differential scanning calorimetry (DSC) is also analyzed by dielectric and conductivity measurements using the impedance spectroscopy techniques. The obtained results show that this transition is protonic by nature.  相似文献   

13.
Hydroxyapatite (Ca5(PO4)3OH) is a well-known bioceramic material used in medical applications because of its ability to form direct chemical bonds with living tissues. This mineral is currently used as a host for rare-earth ions (e.g. Gd3+, Pr3+, Tb3+, etc.) to prepare phosphors that can be used in light emitting devices of different types. In this study Ca5(PO4)3OH:Gd3+,Pr3+ phosphors were prepared by the co-precipitation method and were characterised by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive x-ray spectroscopy and photoluminescence spectroscopy. The x-ray diffraction pattern was consistent with the hexagonal phase of Ca5(PO4)3OH referenced in JCPDS card number 73-0293. The x-ray photoelectron spectroscopy data indicated that Ca2+ occupied two different lattice sites, referred to as Ca1 and Ca2. The photoluminescence data exhibited a narrowband emission located at 313 nm, which is associated with the 6P7/28S7/2 transition of the Gd3+ ion. This emission is classified as ultraviolet B and it is suitable for use in phototherapy lamps to treat various skin diseases. The photoluminescence intensity of the 313 nm emission was enhanced considerably by Pr3+ co-doping.  相似文献   

14.
Two potassium rare-earth polyphosphate single-crystals KLn(PO3)4 (Ln=Ce (1), Eu (2)) have been synthesized by the high-temperature solution reaction and characterized by single-crystal X-ray diffraction. The two isostructural compounds crystallize in the monoclinic system with space group P21, and all cell parameters shrink with the decrease of Ln3+ ion radius. The main structural feature is (PO3)44− wavy chains and infinite tunnels delimited by LnO8 and KO8 polyhedra. The energy band structures, density of states (DOS), and optical response functions for 1 have been calculated with the density functional theory (DFT) method, and the dielectric functions and refractive indices have been discussed. The measurements of the absorption and emission spectra show that 1 exhibits the ultraviolet emissions, and 2 displays the characteristic yellow-red emissions of Eu3+.  相似文献   

15.
By using diamond anvil cell (DAC), high-pressure Raman spectroscopic studies of orthophosphates Ba3(PO4)2 and Sr3(PO4)2 were carried out up to 30.7 and 30.1 GPa, respectively. No pressure-induced phase transition was found in the studies. A methanol:ethanol:water (16:3:1) mixture was used as pressure medium in DAC, which is expected to exhibit nearly hydrostatic behavior up to about 14.4 GPa at room temperature. The behaviors of the phosphate modes in Ba3(PO4)2 and Sr3(PO4)2 below 14.4 GPa were quantitatively analyzed. The Raman shift of all modes increased linearly and continuously with pressure in Ba3(PO4)2 and Sr3(PO4)2. The pressure coefficients of the phosphate modes in Ba3(PO4)2 range from 2.8179 to 3.4186 cm−1 GPa−1 for ν3, 2.9609 cm−1 GPa−1 for ν1, from 0.9855 to 1.8085 cm−1 GPa−1 for ν4, and 1.4330 cm−1 GPa−1 for ν2, and the pressure coefficients of the phosphate modes in Sr3(PO4)2 range from 3.4247 to 4.3765 cm−1 GPa−1 for ν3, 3.7808 cm−1 GPa−1 for ν1, from 1.1005 to 1.9244 cm−1 GPa−1 for ν4, and 1.5647 cm−1 GPa−1 for ν2.  相似文献   

16.
Pyrochlore with mixed-valence Ce was synthesized by firing and annealing Ce(NO3)4, TiO2, and Ca(OH)2 with a stoichiometry of CaCeTi2O7 at 1300 °C. The product contains Ce-pyrochlore, Ce-rich perovskite, CeO2 (cerianite), and minor CaO. Electron energy-loss spectroscopy (EELS) revealed both Ce4+ and Ce3+ in the Ce-pyrochlore with a Ce4+ to total Ce (Ce4+/ΣCe) of 0.80 giving . Cerium in the perovskite and cerianite is dominated by Ce3+ and Ce4+, respectively. High-resolution transmission electron microscope (HRTEM) images show that the boundary between Ce-pyrochlore and Ce-rich perovskite is semi-coherently bonded. The orientational relationship between the neighboring Ce-pyrochlore and Ce-rich perovskite is not random. Ce-pyrochlore (CaCeTi2O7) is a chemical analogue for CaPuTi2O7, which is a proposed ceramic waste form for deposition of excess weapons-usable Pu in geological repositories. It is postulated, based on the presence of Ce3+ in the Ce-pyrochlore, that neutron poisons such as Gd can be incorporated into the CaPuTi2O7 phase.  相似文献   

17.
Raman and FTIR spectra of CaFeTi(PO4)3 and CdFeTi(PO4)3 are recorded and analyzed. The observed bands are assigned in terms of vibrations of TiO6 octahedra and PO4 tetrahedra. The symmetry of TiO6 octrahedra and PO4 tetrahedra is lowered from their free ion symmetry. The presence of Fe3+ ion disrupts the Ti-O-P-O-Ti chain and leads to the distortion of TiO6 octrahedra and PO4 tetrahedra. The PO43− tetrahedra in both crystals are linearly distorted. The covalency bonding factor of PO43− polyanion of both the crystals are calculated from the Raman spectra and compared to that of other Nasicon-type systems. The numerical values of covalency bonding factor indicates that there is a reduction in redox energy and cell voltage and is attributed to strong covalency of PO43− polyanionin.  相似文献   

18.
Single crystals of organic nonlinear optical (NLO) materials l-Histidine nitrate (C6H10N3O2)+ · (NO3) and l-Cysteine tartrate monohydrate (C3H8NO2S)+ · (C4H5O6) · H2O were grown by submerged seed solution method. Characterization of the crystals was made using single crystal X-ray diffraction. Fourier transform infrared (FTIR) spectroscopic studies, optical behaviour such as UV-visible-NIR absorption spectra and second harmonic generation (SHG) conversion efficiency were investigated to explore the NLO characteristics of the above materials. Microhardness measurements and dielectric studies of the compounds were also carried out.  相似文献   

19.
Infrared and Raman spectra of polycrystalline KUO2PO4 · 3 H2O (KUP) and its isotopic derivatives KUO2P18O4 · 3 H2O and KUO2PO4 · 3 D2O have been investigated in the 4000-10-cm?1 range at different temperatures. An assignment of the bands in terms of UO2, PO4 and H2O vibrations has been proposed. Combined differential scanning calorimetry and spectroscopic data show two diffuse phase transitions near 130 and 230 K. Comparison of the vibrational spectra of phase I at 300 K and phase IV at 100 K indicates that ordering of the water molecules with subsequent ordering of PO4 tetrahedra on a site with lower symmetry appears to be the main mechanism responsible for the phase transformation. All the six O-H distances of water molecules in phase IV are found to be crystallographically nonequivalent. Conducting ion frequencies and the corresponding force constants have been determined for the analogous compounds MUP with M = K+, Na+, Ag+, NH+4, Tl+ and H3O+ and compared with other properties of these ionic conductors. Conductivity mechanisms in these materials are discussed.  相似文献   

20.
The series of whitlockite compounds Ca3(PO4)2 and Ca9Ln(PO4)7 (Ln = Pr, Eu, Tb, Dy, Ho, Er, Lu) was studied in radioluminescence (RL) and thermally stimulated luminescence (TSL) excited by X-rays. f-f emission lines of Ln3+ were observed in RL for Ca9Ln(PO4)7 (Ln = Pr, Eu, Tb, Dy, Ho, Er) whereas d-d emission band of the impurity Mn2+ was observed in Mn:Ca3(PO4)2 and Mn:Ca9Lu(PO4)7 at 655 nm. In TSL, the Eu, Ho and Er compounds did not show any signal. As Eu3+, Ho3+ and Er3+ present the highest Ln3+/Ln4+ ionization potential (IP) of the series, this was interpreted as the inability of these lanthanides to trap a hole. On the contrary Pr3+ in Ca9Pr(PO4)7, Tb3+ in Ca9Tb(PO4)7, Dy3+ in Ca9Dy(PO4)7, Mn2+ in Mn:Ca3(PO4)2 and Mn:Ca9Lu(PO4)7 were identified as hole traps and radiative recombination centers in the TSL mechanism. Ca9Tb(PO4)7 was found to be a high intensity green persistent phosphor whereas Mn:Ca9Lu(PO4)7 is a red persistent phosphor suitable for in vivo imaging application.  相似文献   

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