Structural relaxation of scintillating Ce-doped Na–Gd phosphate glass with a nominal composition of Ce:NaGd(PO3)4 was experimentally studied using non-isothermal thermo-mechanical analysis, and the relaxation process was described by the
Tool–Narayanaswamy–Mazurin model. The distribution of relaxation times was expressed by the empirical Kohlrausch–Williams–Watts
relaxation function with relaxation time directly proportional to dynamic viscosity. The model parameters and material constants
were obtained by the nonlinear regression analysis of thermo-mechanical data. It has been concluded that the model used of
structural relaxation correctly describes relaxation processes in studied Ce-doped NaGd(PO3)4 glass. 相似文献
A ETS-10-like topological vanadoarsenate [NH4VO(AsO4)]n1 has been hydrothermally synthesized and structurally characterized by X-ray diffraction. The molecule structural analysis reveals that 1 is constructed by helical [–V–O–]n chains and AsO4 tetrahedra. Crystal data for 1: Orthorhombic, with space group Pnna, a = 13.212(3) Å, b = 10.753(2) Å, c = 6.6266(13) Å, V = 941.4(3) Å3, Z = 8, R1 = 0.0515 and wR2 = 0.1144. 相似文献
Conditions for hydroxyapatite (HAP) synthesis in aqueous solutions by hydrolysis of α-Ca3(PO4)2 were studied. Temperature exerts a substantial effect on the rate of α-Ca3(PO4)2 hydrolysis and also changes the morphology of the reaction products. At 40 °C, the plate-like intersecting (perpendicular to the surface of the initial particles) crystals of HAP grow. Their maximum size after the 24-h hydrolysis is 1–2 µm. Needle like HAP crystals are formed upon boiling of the suspension. The morphology observed for the HAP particles agrees well with the conclusions obtained by analysis of the kinetics of tricalcium phosphate hydrolysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 78–85, January, 2005. 相似文献
Chemical, derivatographic, IR spectral, and X-ray diffraction analyses were used to study thermal transformations in the system CO(NH2)2-H3PO4 and in the same system with addition of KNO3, CsNO3, LiNO3 · 3H2O, and NH4NO3 salts in the temperature range 20–600°C. The influence of the chosen nitrate compounds on the process of reorganization of the constituent ingredients, evolution of nitrogen into the gas phase, yield of the solid residue, and preservation of nitrogen and phosphorus was revealed. 相似文献
Phosphate sulfates M2MgTi(SO4)(PO4)2 (M = alkali metal) prepared by the sol–gel technique with ethanol as salting-out agent were characterized by differential thermal analysis, electron probe microanalysis, and X-ray phase analysis. The crystal structure of the compounds synthesized (M = Na, K) was refined by powder X-ray diffraction. The phase stability of the phosphate sulfates under heating was examined. 相似文献
Phosphates M0.5Ti2(PO4)3 (M = Ni, Zn) were synthesized by the sol-gel method and characterized by the methods of X-ray diffraction, IR spectroscopy, and electronic microprobe analysis. Structures of Ni0.5Ti2(PO4)3 and Zn0.5Ti2(PO4)3 were studied by Rietveld method using the X-ray powder diffraction data. 相似文献
Triple phosphates A2FeTi(PO4)3 (A = Na, Rb) were synthesized by the solid-phase method and studied by electronic microscopy, electron probe X-ray microanalysis, and IR and Mössbauer spectroscopy. The crystal structure of the obtained compounds was refined by X-ray powder diffraction (the Rietveld method). The unit-cell parameters are as follows: for Na2FeTi(PO4)3 (space group R\(\overline 3 \)c, Z = 6), a = 8.6015(1) Å, c = 21.718(1) Å, V = 1391.52(1) Å3; for Rb2FeTi(PO4)3 (space group P213, Z = 4), a = 9.8892(2) Å, V = 967.12(1) Å3. The base of the crystal structures is a mixed octahedral-tetrahedral framework {[FeTi(PO4)3]2?}3∞. Na+ and Rb+ cations are arranged in cavities of the framework. The influence of cationic substitutions on the change of the structural type of the isoformular compounds A2FeTi(PO4)3 (A = Na, Rb) was considered. 相似文献
Double phosphate Ba1.5Fe2(PO4)3 was synthesized and structurally studied. Single crystals were synthesized by the fusion method. Cubic crystals, Z = 4, space group P213, a = 9.866(1) Å. This structure is built of polyhedrons of four types: PO4 tetrahedrons, two virtually regular FeO6 octahedrons, BaO12 twelve-vertex polyhedrons, and BaO9 nine-vertex polyhedrons. These polyhedrons share common oxygen vertices to form three-dimensional [Fe2(PO4)3]3∞ framework containing barium atoms in cavities. 相似文献
The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide (LVP/N-RGO) composite was prepared by a facile one-pot hydrothermal method and evaluated as cathode material for lithium-ion batteries. It is clearly seen that the novel porous structure of the as-prepared LVP/N-RGO significantly facilitates electron transfer and lithium-ion diffusion, as well as markedly restrains the agglomeration of Li3V2(PO4)3 (LVP) nanoparticles. The introduction of N atom also has positive influence on the conductivity of RGO, which improves the kinetics of electrochemical reaction during the charge and discharge cycles. It can be found that the resultant LVP/N-RGO composite exhibits superior rate properties (92 mA h g?1 at 30 C) and outstanding cycle performance (122 mA h g?1 after 300 cycles at 5 C), indicating that nitrogen-doped RGO could be used to improve the electrochemical properties of LVP cathodes for high-power lithium-ion battery application.
Graphical abstract The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide composite with significantly accelerating electron transfer and lithium-ion diffusion exhibits superior rate property and outstanding cycle performance.
Transport properties of ionic salt CsH5(PO4)2 are studied by the impedance method. The salt’s bulk conductivity ranges from 10?8 to 10?4 S cm?1 in the temperature interval 90 to 145°C. The apparent activation energy is high (1.6–2.0 eV). The conductivity is slightly anisotropic: it is maximum in the [001] direction and minimum in the [100] direction (~5.6 and 1 times × 10?6 S cm?1, respectively, at 130°C). The conductivity of polycrystalline samples is higher by 1–2 orders of magnitude, and the activation energy drops to 1.05 eV due to the formation of a pseudoliquid layer with a high proton mobility at the intercrystallite boundary. The salt’s thermodynamic properties are examined by differential scanning calorimetry and thermogravimetry. No phase transitions are discovered in the salt up to the melting point (151.6°C), with the melting enthalpy equal to ~34 kJ mol?1. The crystallization occurs at lower temperatures (107°C) and the crystallization enthalpy (?18 kJ mol?1) is lower than the melting enthalpy. The melting is accompanied by slow decomposition of the salt. Factors affecting the proton transport in the salt are analyzed. 相似文献
A series of Li3V2(PO4)3/C composites with different amounts of carbon are synthesized by a combustion method. The physical and electrochemical properties of the Li3V2(PO4)3/C composites are investigated by X-ray diffraction, element analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and electrochemical measurements. The effects of carbon content of Li3V2(PO4)3/C composites on its electrochemical properties are conducted with cyclic voltammetry and electrochemical impedance. The experiment results clearly show that the optimal carbon content is 4.3 wt %, and more or less amount of carbon would be unfavorable to electrochemical properties of the Li3V2(PO4)3/C electrode materials. The results would provide some basis for further improvement on the Li3V2(PO4)3 electrode materials. 相似文献
The new phosphate Cs2Mn0.5Zr1.5(PO4)3 was synthesized for the first time and characterized by X-ray diffraction. Its crystal structure was refined in space group P213, Z = 4 at 25°C (a = 10.3163(1) Å, V = 1097.93(1) Å3), by the Rietveld method using the powder X-ray diffraction data. The structure is built of an octahedral-tetrahedral framework {[Mn0.5Zr1.5(PO4)3]2?}3∞ with cesium atoms being located in large cavities. The hydrolytic stability of the powdered phosphate containing 137Cs radionuclide was studied. The minimum achieved 137Cs leaching rate was 4 × 10?8 g/cm2 day. 相似文献
Crystal structures of (NH4)3ZrF7 (I) and (NH4)3NbOF6 (II) are refined by X-ray diffraction at room temperature. The compounds are isostructural and belong to the structural type of elpasolite: space group F23; a(I) = 9.4185(3) Å, a(II) = 9.3371(5) Å; V(I) = 835.50(5) Å3, V(II) = 814.02(8) Å3; Z = 4; R(I) = 0.0145, and R(II) = 0.0138. The refinement of the structures in the space group Fm3m yields abnormally short X-X distances in the pentagonal bipyramid MX7 (X = F, O). The oxygen atom in II is identified by Nb-X distances and occupies one of the axial vertices of the bipyramid. The Nb atom in II is statistically distributed over the position 24f, while Zr in I resides in the symmetry center. The pentagonal bipyramid MX7 has six independent orientations in I and twelve in II. One of three crystallographically independent ammonium groups of the structures is disordered over six or twelve equivalent orientations. 相似文献
In the work the structural and thermodynamic characteristics of zirconium tetrahydroborate Zr(BH4)4 are considered. The initial compound organized in a cubic lattice was heated from absolute zero to temperatures exceeding the experimental boiling temperature. Temperature dependences of the parameters of the internal structure, energy, and density of molecules in bulk are obtained. It is found that on heating the compound to 300 K its structure is maintained and on further cooling it returns to the initial state. On heating above 400 K the irreversible destruction of the crystal lattice is observed. On further cooling the compound in the solid phase becomes amorphous. It is shown that in the new state the average binding energy is lower than that in the initial one and the cubic lattice has the highest binding energy among the considered Zr(BH4)4 structures. 相似文献
Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) Å3, Z = 1, and Dx = 1.565 g cm?3. The crystal structure has been determined and refined to R = 0.030 and Rw(F2) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H2PO4]nn? chains with (C6H16N2)2+ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, 13C and 31P MAS NMR spectroscopies and Ab initio calculations. 相似文献
The densities of two systems of molten mixtures (NaF/AlF3)—NaVO3 and (NaF/AlF3)—AlPO4 were measured using an Archimedean method. Each molten mixture contained varying amounts of “impurity” constituents. The
measurements were performed at various NaF/AlF3 mole ratios (CR, cryolite ratio), equal to 3, 2.5, 2, and 1.5. 相似文献
The compound [Ni(NH3)6][VO(O2)2(NH3)]2 was prepared and characterized by elemental analysis and vibrational spectra. The single crystal X-ray study revealed that
the structure consists of [Ni(NH3)6]2+ and [VO(O2)2(NH3)]− ions. As a result of weak interionic interactions V′···Op (Op-peroxo oxygen), ([VO(O2)2(NH3)]−)2 dimers are formed in the solid-state. The thermal decomposition of [Ni(NH3)6][VO(O2)2(NH3)]2 is a multi-step process with overlapped individual steps; no defined intermediates were obtained. The final solid products
of thermal decomposition up to 600°C were Ni2V2O7 and V2O5. 相似文献
Calcium borohydride is widely studied as a hydrogen storage material. However, investigations on calcium borohydride from a cluster perspective are seldom found. The geometric structures and binding energies of [Ca(BH4)2]n (n = 1–4) clusters are determined using density function theory (DFT). For the most stable structures, vibration frequency, natural bond orbital (NBO) are calculated and discussed. The charge transfer from (BH4) to Ca was observed. Meanwhile, we also study the LUMO–HOMO gap (Eg) and the B–H bond dissociation energies (BDEs). [Ca(BH4)2]3 owns higher Eg, revealing that trimer is more stable than the other forms. Structures don’t change during optimization after hydrogen radical removal, showing that calcium borohydride could possibly be used as a reversible hydrogen storage material. [Ca(BH4)2]4 has the smallest dissociation energy suggesting it releases hydrogen more easily than others. 相似文献
The macroporous Li3V2(PO4)3/C composite was synthesized by oxalic acid-assisted carbon thermal reaction, and the common Li3V2(PO4)3/C composite was also prepared for comparison. These samples were characterized by X-ray diffraction (XRD), scanning electron
microscope (SEM), and electrochemical performance tests. Based on XRD and SEM results, the sample has monoclinic structure
and macroporous morphology when oxalic acid is introduced. Electrochemical tests show that the macroporous Li3V2(PO4)3/C sample has a high initial discharge capacity (130 mAh g−1 at 0.1 C) and a reversible discharge capacity of 124.9 mAh g−1 over 20 cycles. Moreover, the discharge capacity of the sample is still 91.5 mAh g−1, even at a high rate of 2 C, which is better than that of the sample with common morphology. The improvement in electrochemical
performance should be attributed to its improved lithium ion diffusion coefficient for the macroporous morphology, which was
verfied by cyclic voltammetry and electrochemical impedance spectroscopy. 相似文献