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1.
How the structural changes take place in LiMnyFe1−yPO4-type cathode materials during lithium extraction/insertion is an important issue, especially on if they go through the single-phase reaction (i.e., solid solution reaction) or the two-phase reaction regions. Here we report the studies on the phase transition behaviors of a carbon coated Li1−xMn0.5Fe0.5PO4 (CLi1−xMn0.5Fe0.5PO4, 0.0  x  1.0) sample during the first charge using in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques. The combination of in situ XAS and XRD results clearly identify two two-phase coexistence regions at two voltage plateaus of 3.6 (Fe2+/Fe3+) and 4.2 V (Mn2+/Mn3+) and a narrow intermediate region which proceeds via single-phase reaction in between two two-phase regions. In addition, simultaneous redox reactions of Fe2+/Fe3+ and Mn2+/Mn3+ in the narrow single-phase region are reported and discussed for the first time.  相似文献   

2.
n-Type (Bi2Te3)0.9–(Bi2−xCuxSe3)0.1 (x=0–0.2) alloys with Cu substitution for Bi were prepared by spark plasma-sintering technique and their structural and thermoelectric properties were evaluated. Rietveld analysis reveals that approximate 9.0% of Bi atomic sites are occupied by Cu atoms and less than 4.0 wt% second phase Cu2.86Te2 precipitated in the Cu-doped parent alloys. Measurements show that an introduction of a small amount of Cu (x0.1) can reduce the lattice thermal conductivity (κL), and improve the electrical conductivity and Seebeck coefficient. An optimal dimensionless figure of merit (ZT) value of 0.98 is obtained for x=0.1 at 417 K, which is obviously higher than those of Cu-free Bi2Se0.3Te2.7 (ZT=0.66) and Ag-doped alloys (ZT=0.86) prepared by the same technologies.  相似文献   

3.
La1−x(PO3)3:Tbx3+ (0<x0.6) were prepared using solid-state reaction. The vacuum ultraviolet (VUV) excitation spectrum of La0.55(PO3)3:Tb0.453+ indicates that the absorption of (PO3)33− groups locates at about 163 and 174 nm and the absorption bands of (PO3)33− groups (174 nm) and La3+–O2− (200 nm) and Tb3+ (213 nm) overlap each other. These results imply that the (PO3)33− groups can efficiently absorb the excited energy around 172 nm and transfer the energy to Tb3+. Under 172 nm excitation, the optimal photoluminescence (PL) intensity is obtained when Tb concentration reaches 0.45 and is about 71% of commercial phosphor Zn1.96SiO4:0.04 Mn2+ with chromaticity coordinates of (0.343, 0.578) and the decay time of about 4.47 ms.  相似文献   

4.
We synthesized uniform-sized nanorods of iron–nickel phosphides from the thermal decomposition of metal–phosphine complexes. Uniform-sized (FexNi1−x)2P nanorods (0x1) of various compositions were synthesized by thermal decomposition of Ni–trioctylphosphine (TOP) complex and Fe–TOP complex. By measuring magnetic properties, we found that blocking temperature and coercive field depend on Ni content in the nanorods. Both parameters were more sensitive to doping compared with bulk samples.  相似文献   

5.
The polar intermetallic compound Ba5Ti12Sb19+x (x0.2) has been synthesized by reaction of the elements. Single-crystal X-ray diffraction analysis revealed that it adopts a new structure type (Ba5Ti12Sb19.102(6), space group , Z=2, a=12.4223(11) Å, V=1916.9(3) Å3). The set of Ba and Sb sites corresponds to the structure of Cu9Al4, a γ-brass type with a primitive cell. A complex three-dimensional framework of Ti atoms, in the form of linked planar Ti9 clusters, is stuffed within the γ-brass-type Ba–Sb substructure. Notwithstanding its relationship to the γ-brass structure, the compound does not appear to conform to the Hume–Rothery electron concentration rules. Band structure calculations on an idealized Ba5Ti12Sb19 model suggest that the availability of bonding states above the Fermi level is responsible for the partial occupation, but only to a limited degree, of an additional Sb site within the structure. Magnetic measurements indicated Pauli paramagnetic behaviour.  相似文献   

6.
New oxysilicates with the general formula ALa3Bi(SiO4)3O and ALa2Bi2(SiO4)3O [ACa, Sr and Ba] are synthesized and characterized. Powder X-ray diffraction of these silicates show that they are isostructural with BiCa4(VO4)3O which has an apatite-related structure. Eu3+ luminescence in the newly synthesized oxysilicates show broad emission lines due to disorder of cations. The relatively high intense magnetic dipole transition 5D07F1 points to a more symmetric environment. The photoluminescence results confirm that the compounds have apatite-related crystal structure.  相似文献   

7.
The SrMn1−xFexO3−δ (x=1/3, 1/2, 2/3) phases have been prepared and are shown by powder X-ray and neutron (for x=1/2) diffraction to adopt an ideal cubic perovskite structure with a disordered distribution of transition-metal cations over the six-coordinate B-site. Due to synthesis in air, the phases are oxygen deficient and formally contain both Fe3+ and Fe4+. Magnetic susceptibility data show an antiferromagnetic transition at 180 and 140 K for x=1/3 and 1/2, respectively and a spin-glass transition at 5, 25, 45 K for x=1/3, 1/2 and 2/3, respectively. The magnetic properties are explained in terms of super-exchange interactions between Mn4+, Fe(4+δ)+ and Fe(3+)+. The XAS results for the Mn-sites in these compounds indicate small Mn-valence changes, however, the Mn-pre-edge spectra indicate increased localization of the Mn-eg orbitals with Fe substitution. The Mössbauer results show the distinct two-site Fe(3+)+/Fe(4+δ)+ disproportionation in the Mn- substituted materials with strong covalency effects at both sites. This disproportionation is a very concrete reflection of a localization of the Fe-d states due to the Mn-substitution.  相似文献   

8.
Polycrystalline samples of the Lu1−xLaxMn2O5 solid solution system were synthesized under moderate conditions for compositions with x up to 0.815. Due to the large difference in ionic size between Lu3+ and La3+, significant changes in lattice parameters and severe lattice strains are present in the solid solution. This in turn leads to the composition dependent thermal stability and magnetic properties. It is found that the solid solution samples with x≤0.487 decompose at a single well defined temperature, while those with x≥0.634 decompose over a temperature range with the formation of intermediate phases. For the samples with x≤0.487, the primary magnetic transition occurs below 40 K, similar to LuMn2O5 and other individual RMn2O5 (R=Bi, Y, and rare earth) compounds. In contrast, a magnetic phase with a 200 K onset transition temperature is dominant in the samples with x≥0.634.  相似文献   

9.
We report the first synthesis and high-temperature in situ X-ray diffraction study of InVO3. Polycrystalline InVO3 has been prepared via reduction of InVO4 using a carbon monoxide/carbon dioxide buffer gas. InVO3 crystallizes in the bixbyite structure in space group Ia−3 (206) with a=9.80636(31) Å with In3+/V3+ disorder on the (8b) and (24d) cation sites. In situ powder X-ray diffraction experiments and thermal gravimetric analysis in a CO/CO2 buffer gas revealed the existence of the metastable phase InVO3. Bulk samples with 98.5(2)% purity were prepared using low-temperature reduction methods. The preparative methods limited the crystallinity of this new phase to approximately 225(50) Å. Magnetic susceptibility and neutron diffraction experiments suggest a spin-glass ground state for InVO3.  相似文献   

10.
Powder neutron diffraction studies show that CaLaMnMoO6 double perovskite crystallizes in monoclinic P21/n, with a=5.56961(9), b=5.71514(9), and β=90.043(1)°. Mn and Mo occupy the 2c and 2d positions, respectively, with 6.0(4)% Mn/Mo anti-site mixing. Temperature-dependent magnetic susceptibility measurements reveal that CaLaMnMoO6 is ferrimagnetic, with TN=92(3) K, below which large magnetic frustration is detected. The zero-field magnetic moment measured at 5 K is about 1.2 μB, comparable to that of ALaMnMoO6 (A=Ba and Sr), but much lower than expected for antiparallel ordering of formally Mn2+ (d5) and Mo5+ (d1). Moreover, no long-range magnetic ordering is observed in neutron diffraction data down to 4 K. The magnetic frustration is discussed in the framework of nearest-neighbors next-nearest-neighbors magnetic frustration.  相似文献   

11.
A recently developed experimental and theoretical procedure is used in order to calculate the magnitude and anisotropy of interaction between a lanthanide and a 3d-metal ion. The general formula of the molecular compounds is [Ln(H2O)3(dmf)4(μ-CN)Fe–(CN)5] · nH2O where 1  n  1,5 and dmf = N,N′-dimethylformamide, abbreviated as [LnFe] from now on. The main parts of this procedure are (a) the evaluation of the effective g-parameters of the lanthanide ion with the help of EPR measurements. (b) The use of dual mode EPR spectroscopy to define the anisotropic exchange interactions with the help of an anisotropic Hamiltonian model. (c) Use of the same magnetic model to fit magnetization and susceptibility data in order to verify the EPR findings.It was possible to define some trends concerning the exchange components of the [DyFe] dimer according to which the antiferromagnetic isotropic exchange constant is smaller than 4 cm−1 and the anisotropic components are [DexcEexc] = [6(1), 0.0] cm−1. Also for the case of [TmFe] and [YbFe] dimers the antiferromagnetic isotropic exchange constant is smaller than 0.3 cm−1 while the anisotropic components are [DexcEexc] = [12.0, 0.0] cm−1 and [DexcEexc] = [0.4(1), 0.0] cm−1, respectively.  相似文献   

12.
13.
The structural characterization, thermogravimetric analysis and electrical properties for solid solution system, (Ba1–xLax)2In2O5+x with perovskite-type structure were investigated. X-ray diffraction showed that the orthorhombic phase was in the range of 0.0<x0.3, the tetragonal phase 0.3<x0.5, and the cubic phase 0.5<x. The sharp transition of electrical conductivity shifted to a lower temperature with increasing x and disappeared at the phase boundary between the orthorhombic and tetragonal phases. This perovskite-related oxide exhibited a pure oxide-ion conduction over the oxygen partial pressure range of 1 atm to 10–3.5 atm, and the electrical conductivity reached the value of 1.610–1 (S cm–1) at 1073 K, which was nearly equal to that of the yttria stabilized zirconia. These properties were successfully explained in terms of disordered oxygen ions.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

14.
Rare-earth ions (Eu3+, Tb3+) doped AMoO4 (A=Sr, Ba) particles with uniform morphologies were successfully prepared through a facile solvothermal process using ethylene glycol (EG) as protecting agent. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra and the kinetic decays were performed to characterize these samples. The XRD results reveal that all the doped samples are of high purity and crystallinity and assigned to the tetragonal scheelite-type structure of the AMoO4 phase. It has been shown that the as-synthesized SrMoO4:Ln and BaMoO4:Ln samples show respective uniform peanut-like and oval morphologies with narrow size distribution. The possible growth process of the AMoO4:Ln has been investigated in detail. The EG/H2O volume ratio, reaction temperature and time have obvious effect on the morphologies and sizes of the as-synthesized products. Upon excitation by ultraviolet radiation, the AMoO4:Eu3+ phosphors show the characteristic 5D07F1–4 emission lines of Eu3+, while the AMoO4:Tb3+ phosphors exhibit the characteristic 5D47F3–6 emission lines of Tb3+. These phosphors exhibit potential applications in the fields of fluorescent lamps and light emitting diodes (LEDs).  相似文献   

15.
To get some insight by conclusions of analogy into the drying process of alcoholic aluminium fluoride sol–gels [AlF3/(ROH)x], the structures of α- and β-AlF33H2O as well as of the nonahydrate AlF39H2O are reinvestigated and discussed based on X-ray single crystal structural data. In addition, neutron diffraction experiments of the latter allowed the refinement of proton positions. In accordance with crystal structures, low-temperature solid state 27Al-, 1H- and 19F-MAS NMR spectra convincingly confirm the structural similarity between α-AlF33H2O and AlF39H2O, while the β-phase material is structurally different forming chain structures. Thermal analysis of AlF3/(ROH)x gave evidence for discrete AlF3:ROH ratios of only 1:0.45 and 1:0.1, and solution NMR showed some similarities between aqueous and alcoholic systems.  相似文献   

16.
The rotational barriers between the configurational isomers of two structurally related push–pull 4-oxothiazolidines, differing in the number of exocyclic CC bonds, have been determined by dynamic 1H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl3 at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG# 98.5 kJ/mol (at 298 K). The variable-temperature 1H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d6, possessing the two exocyclic CC bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG# separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the SCCCO entity. The 13C NMR ΔδC(2)C(2′) values, ranging from 58 to 69 ppm in 1ad and 49-58 ppm in 2ad, correlate with the degree of the push-pull character of the exocyclic C(2)C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh COEt > CONHPh > CONHCH2CH2Ph. The decrease of the ΔδC(2)C(2′) values in 2ad has been discussed for the first time in terms of an estimation of the electron donor capacity of the S fragment on the polarization of the CC bonds.  相似文献   

17.
The heat capacity, Cp, of the La1−xSrxCrO3 system and its temperature dependence have been measured by a thermal relaxation technique. Both structural and magnetic phase transitions were detected at temperatures that can be surmised from the phase diagram proposed in previous studies. The observed variation in enthalpy after the first-order structural phase transition, ΔH, showed agreement with those measured by differential scanning calorimetry (DSC). A decrease in the variation in Cp in the second-order magnetic phase transition, ΔCp, with an increase in Sr content was detected, which can be attributed to a decrease in electronic spin configuration entropy with an increase in Sr content. In the dependence of ΔCp on Sr content, a bending point was also observed at x  0.12, at which the crystal system varies from an orthorhombic-distorted perovskite structure to a rhombohedral-distorted perovskite structure.  相似文献   

18.
Zinc triflate (Zn(CF3SO3)2)-doped sol–gel derived di-urea cross-linked POE/siloxane ormolytes (designated as di-ureasils) with ∞>n1 (where the salt content is expressed as n, the molar ratio of oxyethylene moieties to Zn2+ ions) were investigated. The hybrids with n5 are entirely amorphous; those with n>10 are thermally stable up to approximately 305 °C. The siliceous network of representative samples (n=200 and 10) is essentially composed of (SiO)3Si(CH2)-environments and is thus highly branched. The distance between the structural units in samples with 200n10 and n7 is 4.2 and 4.3 Å, respectively. The estimated interdomain distance is 11 and 13 Å for xerogels with 200n20 and n10, respectively. At n=1 a crystalline POE/Zn(CF3SO3)2 complex of unknown stoichiometry is formed. The conductivity maxima are located at n=60 () and n=20 () at 30 and 100 °C, respectively.  相似文献   

19.
Powder neutron and X-ray diffraction studies show that the double perovskites in the region 0?x?1 exhibit two crystallographic modifications at room temperature: monoclinic P21/n and tetragonal I4/m, with a boundary at 0.75<x<0.9. Magnetic susceptibility measurements indicate that for x=0 and 0.5 Sr2−xLaxMnWO6 orders antiferromagnetically (AFM) at 15 and 25 K, respectively, for 0.75?x<1.0, a contribution of weak ferromagnetism (FM), probably due to canted-AFM order, increases with increasing x. The end point compound SrLaMnWO6 shows the strongest FM cluster effect; however, no clear evidence of magnetic order is discernable down to 4.2 K. X-ray absorption spectroscopy (XAS) confirms Mn2+ and mixed-valent W6+/5+ formal oxidation states in Sr2−xLaxMnWO6.  相似文献   

20.
The oxidation of the n = 1 Ruddlesden-Popper phase, Sr2MnO3.5+x, where 0 ≤ x ≤ 0.5 has been investigated using a combination of in-situ diffraction techniques. In agreement with previous reports the room temperature structure of Sr2MnO3.5+x was determined to be monoclinic crystallising in space group P21/c. On heating in air the material undergoes rapid oxidation at a relatively modest temperature, ∼275 °C. The oxidation process is coincident with a significant change in the structure, with the material now adopting a tetragonal I4/mmm structure. In the oxygen deficient phase where x > 0 the Mn coordination is square pyramidal, with a sixth partially occupied oxygen position giving rise to octahedral coordination. Oxidation of Sr2MnO3.5+x results in the filling of the partially occupied O4 positions and a resulting increase in symmetry, with the Mn coordination now adopting solely a distorted octahedral environment.  相似文献   

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