Thermodynamic stability, structural and electrical characterization of mixed ionic and electronic conductor La2Mo2O(8.96)

Thermogravimetric analysis (TGA) technique in controlled oxygen partial pressure (pO(2)) atmospheres has been used to obtain equilibrium oxygen content data as a function of pO(2) on the La(2)Mo(2)O(9-δ) system resulting from the partial reduction of fast oxide-ion conductor La(2)Mo(2)O(9) (LM). Thermodynamic conditions for stabilization of crystalline La(7)Mo(7)O(30) and amorphous La(2)Mo(2)O(7-y) at 718 °C have been determined and discussed. At 608 °C, the compound reported for the first time La(2)Mo(2)O(8.96) (LM896) has been found. The crystalline form and transition temperature in LM896 have been identified by X-ray diffraction at room temperature (XRD) and at controlled temperature. Conductivity curves obtained by electrochemical impedance spectroscopy (EIS) as a function of temperature for both LM and LM896 have been compared. The results indicate that LM896 is a mixed ionic and electronic conductor (MIEC).     

Study of molecular dynamics and the solid state phase transition mechanism for unsymmetrical thiopyrophosphate using X-ray diffraction, DFT calculations and NMR spectroscopy

Differential scanning calorimetry (DSC) and low-temperature X-ray diffraction studies showed that 2-thio-(5,5-dimethyl-1,3,2-dioxaphosphorinanyl)2'-oxo-dineopentyl-thiophosphate (compound 1) undergoes reversible phase transition at 203 K related to the change of symmetry of the crystallographic unit. Solid state NMR spectroscopy was used to establish the dynamic processes of aliphatic groups and the phosphorus skeleton. 13C and 31P variable temperature NMR studies as well as T1 and T1rho measurements of relaxation times revealed the different mode of molecular motion for each neopentyl residue directly bonded to phosphorus. It is concluded that molecular dynamics of aliphatic groups causes different van der Waals interactions in the crystal lattice and is the driving force of phase transition for compound 1. Finally, we showed that very sharp phase transition temperature makes compound 1 an excellent candidate as a low-temperature NMR thermometer in the solid phase.     

Comprehensive interpretation of a substitution effect on an order-disorder phase transition in A(1-x)MxW2O(8-y) (A = Zr, Hf; M = trivalent cations) and other ZrW2O8-based solid solutions

Hf(1-x)Lu(x)W(2)O(8-y) solid solutions up to x = 0.04, based on a negative thermal expansion material HfW(2)O(8), were synthesized by a solid state reaction method. X-ray diffraction experiments of these solid solutions from 90 to 560 K indicated thermal contraction with increasing temperature. Temperatures of order-disorder phase transition (T(trs)) associated with the orientation of WO(4) tetrahedra were determined from disappearance of a characteristic diffraction peak (310). The T(trs) of the solid solutions drastically decreased with increasing Lu content. Saturated order parameters (eta(s)) associated with the orientational order of the WO(4) pairs were estimated from the characteristic diffraction peak at sufficient low temperature. These behaviors of Hf(1-x)Lu(x)W(2)O(8-y) are consistent with those of Zr(1-x)M(x)W(2)O(8-y) (M = Sc, Y, In, Lu). The drastic suppression of T(trs) in Hf(1-x)Lu(x)W(2)O(8-y) can be interpreted in the framework of a model proposed for Zr(1-x)M(x)W(2)O(8-y), which states the existence of a local nanoregion including the WO(4) pairs having the frozen-in orientational disorder. To understand the substitution effect on the order-disorder phase transition comprehensively, classification based on the saturated order parameter eta(s) of the phase transition of AW(2)O(8) (A = Hf, Zr)-based solid solutions was carried out and discussed.     

Al掺杂对Li(AlyCo1-y)O2材料结构的影响

报道了在800℃烧结制备的新型锂二次电池正极材料Li(AlyCo_1-y)O₂(y=0,0.11)的X射线衍射结果和由此而揭示的结构演化过程.研究表明,y≤0.5时,材料呈单相,0.6≤y≤0.9时,材料呈两相[Li(AlyCo_1-y)O₂,C-LiAlO₂]共存状态,y=1时,材料又呈单相,为LiAlO₂相.Li(AlyCo_1-y)O₂材料中y值的上限即Al的最大固溶度在0.5左右.在单相区(y≤0.5),随着Al掺杂的增多,Li(AlyCo_1-y)O₂材料晶格结构参数发生变化,a轴缩短,c轴变长,c/a比基本呈线性增加,材料的层状属性更加明显.     

Multinuclear solid-state NMR spectroscopy of doped lanthanum fluoride nanoparticles

Multinuclear solid-state NMR spectroscopy and powder X-ray diffraction (XRD) experiments are applied to comprehensively characterize a series of pure and lanthanide-doped LaF3 nanoparticles (NPs) that are capped with di-n-octadectyldithiophosphate ligands (Ln3+ = diamagnetic Y3+ and Sc3+ and paramagnetic Yb3+ ions), as well as correlated bulk microcrystalline materials (LaF3, YF3, and ScF3). Solid-state 139La and 19F NMR spectroscopy of bulk LaF3 and the LaF3 NPs reveal that the inorganic core of the NP retains the LaF3 structure at the molecular level; however, inhomogeneous broadening of the NMR powder patterns arises from distributions of 139La and 19F NMR interactions, confirming a gradual change in the La and F site environments from the NP core to the surface. 139La and 19F NMR experiments also indicate that low levels (5 and 10 mol %) of Ln3+ doping do not significantly change the LaF3 structure in the NP core. Similar doping levels of paramagnetic Yb3+ ions severely broaden 19F resonances, but only marginally effect 139La powder patterns, suggesting that the dopant ions are uniformly distributed throughout the NP core and occupy vacant La sites. Measurements of 139La T1 and T2 relaxation constants are seen to vary between the bulk material and NPs and between samples with diamagnetic and paramagnetic dopants. 45Sc NMR experiments confirm that the dopants are integrated into the La sites of the LaF3 core. Solid-state 1H and 31P magic-angle spinning (MAS) NMR spectra aid in probing the nature of the capping ligands and their interactions at the NP surface. 31P cross-polarization (CP)/MAS NMR experiments identify not only the dithiophosphate head groups but also thiophosphate and phosphate species which may form during NP synthesis. Finally, 19F-31P CP/MAS and 1H MAS experiments confirm that ligands are coordinated to the NP surface.     

Revisiting the polyoxometalate-based late-transition-metal-oxo complexes: the "oxo wall" stands

Terminal oxo complexes of the late transition metals Pt, Pd, and Au have been reported by us in Science and Journal of the American Chemical Society. Despite thoroughness in characterizing these complexes (multiple independent structural methods and up to 17 analytical methods in one case), we have continued to study these structures. Initial work on these systems was motivated by structural data from X-ray crystallography and neutron diffraction and (17)O and (31)P NMR signatures which all indicated differences from all previously published compounds. With significant new data, we now revisit these studies. New X-ray crystal structures of previously reported complexes K(14)[P(2)W(19)O(69)(OH(2))] and "K(10)Na(3)[Pd(IV)(O)(OH)WO(OH(2))(PW(9)O(34))(2)]" and a closer examination of these structures are provided. Also presented are the (17)O NMR spectrum of an (17)O-enriched sample of [PW(11)O(39)](7-) and a careful combined (31)P NMR-titration study of the previously reported "K(7)H(2)[Au(O)(OH(2))P(2)W(20)O(70)(OH(2))(2)]." These and considerable other data collectively indicate that previously assigned terminal Pt-oxo and Au-oxo complexes are in fact cocrystals of the all-tungsten structural analogues with noble metal cations, while the Pd-oxo complex is a disordered Pd(II)-substituted polyoxometalate. The neutron diffraction data have been re-analyzed, and new refinements are fully consistent with the all-tungsten formulations of the Pt-oxo and Au-oxo polyoxometalate species.     

The effects of Mo doping on 0.3Li[Li0.33Mn0.67]O2·0.7Li[Ni0.5Co0.2Mn0.3]O2 cathode material

Mo doped Li excess transition metal oxides formulated as 0.3Li[Li(0.33)Mn(0.67)]O(2)·0.7Li[Ni(0.5-x)Co(0.2)Mn(0.3-x)Mo(2x)]O(2) were synthesized using the co-precipitation process. The effects of the substitution of Ni and Mn with Mo were investigated for the density of the states, the structure, cycling stability, rate performance and thermal stability by tools such as first principle calculations, synchrotron X-ray diffraction, field-emission SEM, solid state (7)Li MAS nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), elemental mapping by scanning TEM (STEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and a differential scanning calorimeter (DSC). It was confirmed that high valence Mo(6+) doping of the Li-excess manganese-nickel-cobalt layered oxide in the transition metal enhanced the structural stability and electrochemical performance. This increase was due to strong Mo-O hybridization inducing weak Ni-O hybridization, which may reduce O(2) evolution, and metallic behavior resulting in a diminishing cell resistance.     

Synthesis of New Solid Solutions on Neodymium-stabilized La2Mo2O9

Oxide ion conductors form a class of materials which are widely sought for and studied since they can be used in different field among solid oxide fuel cells (FOFC), oxygen sensors, oxygen pumping devices, or oxygen-permeable membrane catalysts, for instance1-3. Now research focuses on the oxide ion conductors with new structure and improving the conductivity or lowering the operating temperature. Recently P.Lacorre et al.4 have reported a novel oxide-ion conductor based on La2Mo2O9. F.…     

A monovacant heteropolytungstate thioderivative: Synthesis and characterization of [(PW11O39)2(H4Mo4S4O6)](10-) and related isomers

[(PW(11)O(39))(2)(Mo(4)S(4)O(4)(OH(2))(2))](10-) anions were obtained through the stereospecific addition of the [Mo(2)S(2)O(2)](2+) oxothiocation to the monovacant alpha-[PW(11)O(39)](7-) anion. K(10)[(PW(11)O(39))(2)(Mo(4)S(4)O(4)(OH(2))(2))].25H(2)O has been isolated as crystals and characterized by X-ray diffraction. The structure revealed a "sandwich-like" dimer of two alpha-[PW(11)O(39)](7-) subunits assembled by the noteworthy central cluster [H(4)Mo(4)S(4)O(6)]. The crystallization of the crude product produces an isomerically pure compound, which was characterized by (31)P and (183)W NMR. IR data were also supplied. In solution, the compound isomerizes, giving a second diastereoisomer. A kinetic experiment, carried out by (31)P NMR, allowed the conditions of the thermodynamic equilibrium to be determined. A structural relationship between the two isomers is proposed, fully consistent with NMR data. Cisoid and transoid isomers result in the relative disposition of each [PW(11)O(39)](7-) subunit, either staggered or eclipsed. An investigation of the formation of the [Mo(2)O(2)S(2)](2+) unit from the polycondensed cyclic precursor [Mo(10)S(10)O(10)(OH)(10)(H(2)O)(5)] and the aggregation process resulting in the oxothio [(PW(11)O(39))(2)(Mo(4)S(4)O(4)(OH(2))(2))](10-) compound has been undertaken. The studies were monitored by (31)P NMR and UV-vis spectroscopies. The reaction is quantitative in nearly stoichiometric conditions.     

Characterization of a new hexasodium diphosphopentamolybdate hydrate, Na6[P2Mo5O23]x7H2O, by 23Na MQMAS NMR spectroscopy and X-ray powder diffraction

A novel hexasodium disphosphopentamolybdate hydrate, Na6[P2Mo5O23]x7H2O, has been identified using X-ray powder diffraction, 1H, 23Na, and 31P magic-angle spinning (MAS) NMR, and 23Na multiple-quantum (MQ) MAS NMR. Powder XRD reveals that the hydrate belongs to the triclinic spacegroup P1 with cell dimensions a = 10.090(3) A, b = 15.448(5) A, c = 8.460(4) A, alpha = 101.45(6) degrees, beta = 104.09(2) degrees, gamma = 90.71(5) degrees, and Z = 2. The number of water molecules of crystallization has been determined on the basis of a quantitative evaluation of the 1H MAS NMR spectrum, the crystallographic unit cell volume, and a hydrogen content analysis. The 23Na MQMAS NMR spectra of Na6[P2Mo5O23]x7H2O, obtained at three different magnetic fields, clearly resolve resonances from six different sodium sites and allow a determination of the second-order quadrupolar effect parameters and isotropic chemical shifts for the individual resonances. These data are used to determine the quadrupole coupling parameters (CQ and eta Q) from simulations of the complex line shapes of the central transitions, observed in 23Na MAS NMR spectra at the three magnetic fields. This analysis illustrates the advantages of combining MQMAS and MAS NMR at moderate and high magnetic fields for a precise determination of quadrupole coupling parameters and isotropic chemical shifts for multiple sodium sites in inorganic systems. 31P MAS NMR demonstrates the presence of two distinct P sites in the asymmetric unit of Na6[P2Mo5O23].7H2O while the 31P chemical shielding anisotropy parameters, determined for this hydrate and for Na6[P2Mo5O23]x13H2O, show that these two hydrates can easily be distinguished using 31P MAS NMR.     

31P NMR as a tool for studying incorporation of Ni, Co, Fe, and Mn into aluminophosphate zeotypes

The incorporation of moderate amounts of Ni(II), Co(II), Fe(II/III), and Mn(II/III) into aluminophosphate zeotype AlPO4-34 and Fe(II/III) into aluminophosphate zeotype AlPO4-36 was studied by broadline 31P NMR. The technique provided direct evidence on isomorphous substitution of framework aluminum by transition metals and allowed us to determine the extent of the substitution. 31P NMR proved to be complementary to other spectroscopic techniques such as X-ray absorption spectroscopy (XAS), M?ssbauer, electron paramagnetic resonance (EPR), and electron nuclear double resonance (ENDOR) spectroscopies. The position of the NMR signal belonging to phosphorus in the P(OAl)3(OMe) environment depended mostly on the magnitude of the hyperfine interaction between a phosphorus nucleus and an unpaired electron, which was delocalized from the transition metal atom Me by covalent bonding. The width of the NMR signal was dominated by dipolar coupling among phosphorus nuclei and nearest paramagnetic centers. In addition, broadline NMR of ethylenediamine-templated manganese phosphate (C2H10N2)[Mn2(HPO4)3(H2O)], which was used as a model compound, showed that on the basis of line positions and line widths different 31P signals could easily be assigned to different phosphorus crystallographic sites. The technique could thus be applied to extract valuable structural information about metal phosphates as well.     

La2(Mo1-xVx)2O9-α的制备及其导电性

采用固相法合成了系列陶瓷样品La₂(Mo_1-xV_x)₂O_9-α (x=0.02, 0.04, 0.06, 0.08). 粉末X射线衍射(XRD)结果表明样品具有单一立方相La₂Mo₂O₉结构. 采用气体浓差电池、电化学阻抗等电化学方法研究了陶瓷样品在823-1123 K下的导电特性. 系列陶瓷样品已完全抑制La₂Mo₂O₉母体在853 K附近的相变; 各样品在干燥及湿润氧气气氛中几乎为纯氧离子导体, 质子导电性可忽略不计; 氧离子电导率σ随掺杂离子浓度的变化为σ(x=0.02)<σ(x=0.08)<σ(x=0.06)<σ(x=0.04), 这与晶胞自由体积大小的次序完全一致, x=0.04样品具有最高的氧离子电导率0.051 S·cm^-1; 氧分压与电导率的关系表明, 在高氧分压气氛中样品是纯的氧离子导体, 在低氧分压气氛中是氧离子与电子的混合导体.     

Structural studies of NaPO3-MoO3 glasses by solid-state nuclear magnetic resonance and Raman spectroscopy

Vitreous samples were prepared in the (100 - x)% NaPO(3)-x% MoO(3) (0 相似文献   

Defects in doped LaGaO3 anionic conductors: linking NMR spectral features, local environments, and defect thermodynamics

Doped lanthanum gallate perovskites (LaGaO(3)) constitute some of the most promising electrolyte materials for solid oxide fuel cells operating in the intermediate temperature regime. Here, an approach combining experimental multinuclear NMR spectroscopy with density functional theory total energy and GIPAW NMR calculations yields a comprehensive understanding of the structural and defect chemistries of Sr- and Mg-doped LaGaO(3) anionic conductors. The DFT energetics demonstrate that Ga-V(O)-Ga (V(O) = oxygen vacancy) environments are favored (vs Ga-V(O)-Mg, Mg-V(O)-Mg and Mg-O-Mg-V(O)-Ga) across a range y = 0.0625, 0.125, and 0.25 of fractional Mg contents in LaGa(1-y)Mg(y)O(3-y/2). The results are interpreted in terms of doping and mean phase formation energies (relative to binary oxides) and are compared with previous calculations and experimental calorimetry data. Experimental multinuclear NMR data reveal that while Mg sites remain six-fold coordinated across the range of phase stoichiometries, albeit with significant structural disorder, a stoichiometry-dependent minority of the Ga sites resonate at a shift consistent with Ga(V) coordination, demonstrating that O vacancies preferentially locate in the first anion coordination shell of Ga. The strong Mg-V(O) binding inferred by previous studies is not observed here. The (17)O NMR spectra reveal distinct resonances that can be assigned by using the GIPAW NMR calculations to anions occupying equatorial and axial positions with respect to the Ga(V)-V(O) axis. The disparate shifts displayed by these sites are due to the nature and extent of the structural distortions caused by the O vacancies.     

17O NMR in room temperature phase of La2Mo2O9 fast oxide ionic conductor

A room temperature (17)O NMR study of La(2)Mo(2)O(9), a fast oxide ionic conductor exhibiting a phase transition at 580 degrees C between a low-temperature alpha-phase and a high-temperature beta-phase, is presented. Four partly overlapping quasi-continuous distributions of oxygen sites are evidenced from 1D magic angle spinning (MAS) and 2D triple quantum MAS NMR experiments. They can be correlated with the three oxygen sites O1, O2 and O3 of the high-temperature crystal structure. The low-temperature phase is characterized by two distributed sites of type O1, which proves that the symmetry is lower than in the cubic high-temperature phase. Two-dimensional experiments show that there is no dynamic exchange process, on the NMR time-scale, between the different oxygen sites at room temperature, which agrees well with conductivity results.     

Cyclic Ti9 keggin trimers with tetrahedral (PO4) or octahedral (TiO6) capping groups

We have synthesized the cyclic Ti 9 Keggin trimers [(alpha-Ti 3PW 9O 38) 3(PO 4)] (18-) ( 1) and [(alpha-Ti 3SiW 9O 37OH) 3(TiO 3(OH 2) 3)] (17-) ( 2), which are both composed of three (Ti 3XW 9O 37) units (X = P or Si) linked via three Ti-O-Ti bridges and a capping group, which is either tetrahedral PO 4 ( 1) or octahedral TiO 6 ( 2). Polyanions 1 and 2 were fully characterized in the solid state (IR, X-ray diffraction, thermogravimetric and elemental analyses) and in solution ( (31)P or (183)W NMR).     

新型氧离子导体La2Mo1.9Al0.1O9-α陶瓷的合成及电性能

通过高温固相法合成了La2Mo1.9Al0.1O9-α陶瓷样品. XRD测试结果表明, 该样品为一立方相结构, Al3＋离子在 Mo6＋位置的固溶摩尔浓度为5%时能完全抑制La2Mo2O9的相变. 采用交流阻抗谱、氧浓差电池、氧泵等电化学方法系统地研究了该陶瓷样品在600～1000 ℃下的离子导电特性. 结果表明, 氧浓差电池电动势的实测值与理论值吻合得很好, 离子迁移数为1, 表明该陶瓷样品在该温度下氧气气氛中为一纯离子导体; 氧浓差电池放电及氧的电化学透过(氧泵)实验结果进一步证实了该样品在氧气气氛中为一纯氧离子导体; 1000 ℃时其氧离子电导率达到了0.12 S&#8226;cm－1, 明显高于相同条件下母体及La2Mo1.9Ga0.1O9-α的氧离子电导率.     

Zirconium arene-phosphonates: chemical and structural characterization of 2-naphthyl- and 2-anthracenylphosphonate systems

Several new zirconium phosphonates incorporating naphthalene and anthracene ring systems and having the general formula Zr(O3PR)1(O3PR')1 [R and R' = -C10H7, -C14H9, -OC4H9, and -OC2H5] have been synthesized. These compounds were chemically characterized using thermal gravimetric analysis (percentage of organic content), infrared spectroscopy (presence of the desired organic functional groups), and solid-state 31P NMR (phosphorus environments), while the structural parameters were determined using X-ray powder diffraction (interlayer d spacings). The d spacings of the zirconium bis(phosphonates) correlate well with a simple predictive model based on the effective length of the organic functional group. The zirconium mixed phosphonates examined are single-phase structures with random mixtures of the organic moieties within the interlayer and possess d spacings that are between those of the two parent zirconium bis(phosphonates).     

Conversion of tricoordinate to hexacoordinate phosphorus. Formation of a phosphorane-phosphatrane system

Reaction of RPCl(2) with tris(2-hydroxy-3-tert-butyl-5-methylbenzyl)amine (4) led to the formation of a tricoordinated phosphonite (1) when R = Ph and to a hexacoordinated phosphorane-phosphatrane (2) when R = Et. The X-ray structures showed that the unreacted hydroxyl group in 1 oxidatively added to phosphorus in 2 leading to the formation of three additional bonds, a P[bond]O, a P[bond]H, and a P[bond]N linkage. In solution, (31)P measurements assisted by solid-state (31)P measurements revealed that each of the compounds existed in both structural forms. VT (31)P established equilibria where the solid-state structures predominated in each case. This is the first example of a conversion of three-coordinate to six-coordinate phosphorus on going from the solid to the solution state and the existence of these two disparate geometries in equilibrium with one another in solution. In the absence of steric protection with the use of an analogous amine (5) without tert-butyl groups, a hydrolysis reaction occurred with PhPCl(2). X-ray analysis revealed an anionic phenylphosphinate structure (3) hydrogen bonded in a cage-like arrangement with the protonated amine. Similar hydrolysis reactions take place with 1 and 2 but much more slowly.