排序方式: 共有12条查询结果,搜索用时 0 毫秒
1.
We investigate the vibrational spectra of crystals of ternary orthophosphates Me7Eu2UO2·(PO4)5 (Me–Na, Rb, Cs) obtained by solid-phase synthesis. We show that in these materials the effect of coordination distorts the
geometry of the PO
4
3−
tetrahedron and decreases its symmetry. We conclude that the PO
4
3−
tetrahedrons in Me7Eu2UO2(PO4)5 occupy two nonequivalent positions in the lattice. The character of manifestation and the number of oscillation frequencies
observed allow the assumption that they have the C3v- and C2-symmetry. This symmetry of two crystallographically nonequivalent groups of PO
4
3−
ensures a complete set of bands in the IR absorption spectra of the crystals investigated. We show that these crystals exhibit
chain structural motifs.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol, 64, No. 4, pp. 467–470, July–August, 1997. 相似文献
2.
F. M. Bautista J. M. Campelo A. Garcia D. Luna J. M. Marinas A. A. Romero M. R. Urbano 《Reaction Kinetics and Catalysis Letters》1997,62(1):47-54
The vapor-phase catalytic alkylation of phenol with methanol and dimethyl carbonate on a series of differently prepared CrPO4 (Cr/P=1) and CrPO4-AlPO4 (CrAIP) catalysts, has been studied at different temperatures (473–673 K). The reaction is first order in phenol, giving
a mixture of O- and C-alkylated products (C-alkylation taking place preferentially at theortho-position). Moreover, dimethyl carbonate is a better methylating agent than methanol. 相似文献
3.
C. DurioA. Daidouh N. ChouaibiC. Pico M.L. Veiga 《Journal of solid state chemistry》2002,168(1):208-216
New sodium orthophosphates of general formula Na2M3(PO4)3 belonging to the alluaudite-type structure have been synthesized and characterized by neutron and X-ray powder diffraction. The nature of the M3 elements (M3=GaMn2, GaCd2, InMn2 and FeMnCd) was chosen in order to analyze their influence on electrical and magnetic properties. The conductivity of these materials was measured by the complex impedance method and the transport mechanism was studied from complex permittivities and modulus formalism. Electrical results including charge/discharge experiments showed two main behaviors: GaCd2 and FeMnCd behave as purely ionic conductors whereas GaMn2 and InMn2 are mixed ionic-electronic conductors. The magnetic susceptibility data reveal the antiferromagnetic behavior of FeMnCd, InMn2 and GaMn2, with a weak ferromagnetic transition at low temperatures. 相似文献
4.
Yan R Sun X Wang X Peng Q Li Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(7):2183-2195
The fundamental understanding of the relationship between crystal structure and the dynamic processes of anisotropic growth on the nanoscale, and exploration of the key factors governing the evolution of physical properties in functional nanomaterials, have become two of the most urgent and challenging issues in the fabrication and exploitation of functional nanomaterials with designed properties and the development of nanoscale devices. Herein, we show how structural and kinetic factors govern the tendency for anisotropic growth of such materials under hydrothermal conditions, and how the crystal structure and morphology influence the optical properties of Ln3+-doped nanocrystals. The synthesis of phase-pure and single-crystalline monoclinic, hexagonal, and tetragonal one-dimensional LnPO4 nanostructures of different aspect ratios by means of kinetically controlled hydrothermal growth processes is demonstrated. It is shown that the tendency for anisotropic growth under hydrothermal conditions can be enhanced simply by modifying the chemical potentials of species in the reaction solution through the use of carefully selected chelating ligands. A systematic study of the photoluminescence of various Eu3+-doped lanthanide phosphates has revealed that the optical properties of these nanophosphors are strongly dependent on their crystal structures and morphologies. 相似文献
5.
The article considers the luminescence-kinetics properties of crystals of ternary uranyl orthephosphates Me7Eu2UO2(PO4)5 (Me — Na, Rb, Cs) obtained by the methods of solid-phase synthesis. The main parameters of conversion of the electron excitation
energy in the donor-acceptor UO
2
2+
—Ln3+ system are determined. The competition between the processes of nonradiative dissipation and energy transfer from UO
2
2+
to Eu3+ has been revealed. It is shown that the rate of the processes of nonradiative transitions in the uranyl complex is determined
by the degree of distortion of its local field, while the luminescence lifetime of the acceptors depends on the energy of
electrostatic interaction between Eu3+ and oxygen atoms of its first coordination sphere.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 333–335, May–June, 2000. 相似文献
6.
Handially Santos Vilela Marcela Charantola Rodrigues Bruna Marin Fronza Rafael Bergamo Trinca Flávio Maron Vichi Roberto Ruggiero Braga 《Crystal Research and Technology》2021,56(12):2100094
Calcium orthophosphates (CaP) synthesis involves several chemical equilibria that define the phases present in the final product. From the biomaterials standpoint, it is important to gain knowledge on how synthesis parameters affect phase formation and particle size. This study evaluates the interaction between temperature (24 or 45 °C) and pH conditions (4.5, 6.5, or drifting) on CaP precipitation in terms of yield, phase formation, density, morphology, and size distribution. Calcium and phosphate solutions (Ca/P = 1.0) are mixed and kept under stirring for 3 h. The precipitate is freeze-dried and characterized. Under drifting pH and pH 4.5, dicalcium phosphate dihydrate (DCPD, CaHPO4 × 2H2O) is the predominant phase at both temperatures; however, some samples also present peaks ascribed to dicalcium phosphate anhydrous (DCPA, CaHPO4). At pH 6.5, diffractograms reveal a mixture of low-crystallinity DCPD and DCPA (24 °C) or low crystallinity hydroxyapatite [HAP, Ca10(OH)2(PO4)6] (45 °C). In spite of the different morphologies (plates or aggregates), particle size remains within a relatively narrow range (D50 = 12–28 µm). DCPD precipitation is favored under more acidic or drifting pH, while HAP is formed under nearly neutral pH 6.5. 相似文献
7.
Phosphorus (P) is ubiquitous in the environment, but its measurement is costly and time-consuming. Sensor-based measurement shows potential, but selection of right metal remains the major challenge due to strong P species dependence on pH. This study examined the feasibility of pure cobalt, molybdenum, and their electrodeposited alloy, Co63Mo42 (wt %), as phosphate sensors. The cobalt, molybdenum and alloy exhibited mixed potential, Nernst potential, and oxidation-reduction (red-ox) mechanisms, respectively. Alloy showed good selectivity over a wide pH range, but high limit of detection and long response time (8–14 minutes). Yet, alloy provides a new opportunity for improving electrochemical phosphate sensors. 相似文献
8.
Some properties of rare earth orthophosphates have been determined by means of synthesis, X-ray diffraction, infrared absorption spectra, and Raman spectra measurements. The results are: (1) a synthesis of new compounds GdPO4.2H2O weinschenkite type, (2) the salt readily lost its water and changed from the weinschenkite to the xenotime form at about 300°C in air, (3) the change phase in rare earth orthophosphates showed that the weinschenkite phase can give rise to rhabdophane or xenotime phases, and (4) the orthorhombic form DyPO4·1.5H2O is explainable in terms of a mixture of rhabdophane and xenotime-structured material. 相似文献
9.
Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXXII. New Orthophosphates of Divalent Chromium — Mg3Cr3(PO4)4, Mg3, 75Cr2, 25(PO4)4, Ca3Cr3(PO4)4 and Ca2, 00Cr4, 00(PO4)4 Solid state reactions via the gas phase led in the systems A3(PO4)2 / Cr3(PO4)2 (A = Mg, Ca) to the four new compounds Mg3Cr3(PO4)4 ( A ), Mg3.75Cr2.25(PO4)4 ( B ), Ca3Cr3(PO4)4 ( C ), and Ca2.00Cr4.00(PO4)4 ( D ). These were characterized by single crystal structure investigations [( A ): P21/n, Z = 1, a = 4.863(2) Å, b = 9.507(4) Å, c = 6.439(2) Å, β = 91.13(6)°, 1855 independend reflections, 63 parameters, R1 = 0.035, wR2 = 0.083; ( B ): P21/a, Z = 2, a = 6.427(2) Å, b = 9.363(2) Å, c = 10.051(3) Å, β = 106.16(3)°, 1687 indep. refl., 121 param., R1 = 0.032, wR2 = 0.085; ( C ): P‐1, Z = 2, a = 8.961(1) Å, b = 8.994(1) Å, c = 9.881(1) Å, α = 104.96(2)°, β = 106.03(2)°, γ = 110.19(2)°, 2908 indep. refl., 235 param., R1 = 0.036, wR2 = 0.111; ( D ): C2/c, Z = 4, a = 17.511(2) Å, b = 4.9933(6) Å, c = 16.825(2) Å, β = 117.95(1)°, 1506 indep. refl., 121 param., R1 = 0.034, wR2 = 0.098]. The crystal structures contain divalent chromium on various crystallographic sites, each showing a (4+n)‐coordination (n = 1, 2, 3). For the magnesium compounds and Ca2.00Cr4.00(PO4)4 a disorder of the divalent cations Mg2+/Cr2+ or Ca2+/Cr2+ is observed. Mg3.75Cr2.25(PO4)4 adopts a new structure type, while Mg3Cr3(PO4)4 is isotypic to Mg3(PO4)2. Ca3Cr3(PO4)4 and Ca2.00Cr4.00(PO4) 4 are structurally very closely related and belong to the Ca3Cu3(PO4)4‐structure family. The orthophosphate Ca9Cr(PO4)7, containing trivalent chromium, has been obtained besides C and D . 相似文献
10.
F. Romain A. Lorriaux-Rubbens F. Wallart L. Benarafa M. Knidiri 《Phase Transitions》2013,86(1-4):33-37
This study by Raman spectrometry of double orthophosphates of lutetium and potassium consists of a systematic analysis of double orthophosphates of the potassium and lanthanide family. In the 10-300 K temperature range three solid-solid phase transitions in this compound are obtained which demonstrate the application of Raman spectrometry to the study of the nature and mechanism of such transitions. 相似文献