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1.
Single crystals of the compound La2Zr2O7 were prepared for the first time and examined by x-ray investigations. La2Zr2O7 crystallizes in the space group O? Fd3m, a = 10.786 Å. The free oxygen parameter, which is characteristic for the pyrochlore structure, was found to be x = 0.295.  相似文献   

2.
Li6Zr2O7 was obtained by annealing an intimate mixture of LiOH · H2O and freshly prepared ZrO2 in a stream of argon. It is monoclinic: C2/c, a = 1 044.5(1), b = 598.9(1), c = 1 020.0(1) pm, β = 100.26(1)°, Z = 4, R = 0.016 for 1 218 F values and 55 variables. The structure is closely related to that of NaCl with an ordered distribution of the metal atoms on the sodium sites while the oxygen atoms occupy seven eighths of the chlorine positions. Li has square pyramidal, Zr octahedral oxygen coordination. The corresponding Hf compound is isotypic: a = 1 040.2(1), b = 596,2(1), c = 1 015.0(1) pm, β = 100.36(1)°. 7Li nuclear magnetic resonance spectra of this compound give no indication for a high mobility of the Li+ ions.  相似文献   

3.
The structural phase transition from fluorite to pyrochlore and the strength of the coordination bond of Zr–O in Gd2Zr2O7 were investigated by XANES spectra of both O and Zr K‐edge. The energy difference of the O K‐edge absorption spectra at 532 and 536 eV was assigned to the crystal field splitting energy of the 4d orbital (ΔE4d, t2g and eg) of the Zr ion. Also, in the samples prepared at higher temperatures, the 536 eV peak moves slightly to higher energy, whereas the absorption energy of 532 eV peak does not shift. A correlation between ΔE4d and the strength of interaction between Zr (4d) and O (2p) orbitals has been found. Furthermore, two Zr K‐edge absorptions at 18020 and 18030 eV of Gd2Zr2O7 have been observed; the splitting energy (ΔE), peak intensity ratio (I18030/I18020), and FWHM of the first derivative of the absorption curve depend on the preparation temperatures. The effect of crystal symmetry and Zr‐O bonding character on the XANES spectral profile was discussed.  相似文献   

4.
采用高温固相反应,以NaF作助熔剂,在1000 ℃的温度下合成了锕系元素Pu的模拟固化体(Gd1-xCex)2Zr2O7+x (0 ≤ x ≤ 0.7).研究了模拟固化体的物相、热膨胀系数(TEC)、热导率(TC)随温度及组成的变化规律.粉末X射线衍射(XRD)测试结果表明: Gd2Zr2O7基质本身呈弱有序烧绿石结构,而用Ce4+取代Gd3+的模拟固化体都呈缺陷萤石结构. (Gd1-xCex)2Zr2O7+x的Ce(3d) X射线光电子能谱(XPS)有六个峰,结合能分别位于881.7, 888.1, 897.8, 900.4, 907.1, 916.1 eV处,与CeO2的XPS图谱非常相似,说明Ce为四价.随着温度的升高,所有样品的热膨胀系数总体上呈增大趋势.在室温至750 ℃附近,大部分样品的热导率随温度的升高而降低,之后热导率又呈小幅上升.在相同温度下,固化体(Gd1-xCex)2Zr2O7+x (0 ≤ x ≤ 0.7)的热膨胀系数及热导率随组成变化呈相同趋势:在0 ≤ x ≤ 0.1范围内随x的增大而增大,随后在x = 0.1-0.7时逐渐减小.  相似文献   

5.
La2Zr2O7 (LZO) formation of bulk powders and of films by chemical solution deposition (CSD) process have been studied using propionates. The treatment involved a one step cycle in the reducing forming gas (Ar-5%H2) to be compatible with Ni-5at%W RABITS. Large amount of residual carbon was found in LZO powders formed in these conditions (10 wt%). The volume fraction of the cube texture in LZO films on Ni-5at%W RABITS was found to be a function of the speed of the gas flown above sample. This phenomenon is discussed in considering the C deposited from the carbon-containing gases emitted during the pyrolysis of the precursor. Using proper conditions (950 °C and the speed of gas of 6.8 × 10?2 m/s), LZO films with good surface crystallinity could be obtained on Ni-5at%W RABITS as demonstrated by X-ray diffraction, electron backscattered diffraction and RHEED. The existence of residual carbon in oxide films is a common question to films deposited by CSD processes under reducing condition.  相似文献   

6.
7.
A combination of modern locally sensitive methods of structure analysis based on the interaction of synchrotron radiation with condensed matter was used to study the formation and evolution of crystal structures, change in the size of crystallites, the type and degree of cationic ordering, and features of the local atomic structures of compounds Ln2Hf2O7 (Ln = Gd, Dy) prepared by heat treatment of X-ray amorphous precursors.  相似文献   

8.
A series of nanocrystalline Gd2Zr2O7 powders has been studied using a combination of X-ray diffraction and X-ray spectroscopy with synchrotron radiation. It has been shown that isothermal annealing of an X-ray amorphous mixed hydroxide first leads to the formation of an oxide nanomaterial with a defect fluorite structure and clearly pronounced nonequivalence of the local environment of the Gd3+ and Zr4+ ions. Increasing heat treatment temperature results in initiation and growth of nanodomains with pyrochlore-type superstructure ordering of cations inside bulkier crystallites of defect fluorite. To adequately describe the evolution of the real nanocrystalline structure of gadolinium zirconate, a combination of X-ray structural methods sensitive to the averaged crystal structure and local atomic structure should be used.  相似文献   

9.
Russian Journal of Electrochemistry - The method of solid-phase sintering was used to synthesize samples of lithium-conducting Li6.4Al0.2La3Zr2O12 solid electrolyte with a garnet structure. Higher...  相似文献   

10.
La2Zr2O7 (LZO) layers have been recently investigated as potential buffer layers for superconducting YBa2Cu3O7–x coated conductors deposited on Ni tapes. Chemical solution deposition was used for LZO layer preparation. X-ray photoelectron spectroscopy (XPS) depth profiling is demonstrated to be an important method for layer characterization in addition to X-ray diffraction techniques. XPS measurements revealed layers that are homogeneous in depth, very smooth, and have no significant impurities. A slight difference to the nominal La:Zr stoichimetry is discussed in combination with structural defects that are suspected from spectral changes during ion sputtering.  相似文献   

11.
本文采用固相法制备了Ta 5+掺杂的石榴石型无机固体电解质Li7-xLa3Zr2-xO12xTa-LLZO),研究了不同的掺杂量对材料性能的影响. 通过X射线发射光谱(XRD)、冷场发射电子扫描电镜(FESEM)和电化学阻抗(EIS)对材料进行物理表征和阻抗测试,并且组装LiFePO4//LLZTO//Li全固态锂电池测试电池的循环稳定性. 结果表明,随着Ta 5+掺杂的增加,材料呈现出一个单一的立方相结构,当Ta 5+掺杂量为14.09wt.%(即x=0.3)时,材料的室温离子电导率达到最大(2.58×10 -4 S·cm -1),呈现出稳定的立方相结构且具有相对较高的致密度(89.16%),并具有较稳定的循环稳定性,经过50个循环后容量保持率依然保持到88.67%左右.  相似文献   

12.
Ultrafine Nd2Hf2O7 powders with the pyrochlore structure are prepared by self-propagating hightemperature synthesis (in the Pechini version). The elemental and phase composition of the powder are studied. Microstructure is studied by scanning electron microscopy. BET specific surface areas are determined. Thermal behavior is studied by TGA/DSC/DTA up to 1473 K. The sintering kinetics of as-synthesized Nd2Hf2O7 powder at various temperatures is studied. Nd2Hf2O7 vaporization in the range 2400–2600 K is studied by Knudsen effusion/mass spectrometry, and the thermodynamic characteristics of this compound are determined.  相似文献   

13.
The Crystal Structure of KPdMIVF7 (MIV = Zr, Hf) Blue single crystals of KPdZrF7 are obtained by heating the binary fluorides in sealed Pt-tubes under dry argon (solid state reaction, T ≈? 720°C, t ≈? 14 d). The compound crystallizes orthorhombically in the space group Pnna-D (Nr. 52); lattice parameters are a = 1 132.3(5) pm, b = 797.5(2) pm, c = 639.8(1) pm; Z = 4 (Four cycle diffractometer data, AED2). According to [F4PdF2/1ZrF5] distortet [PdF6]-octaedra are connected with pentagonal-bipyramidal [ZrF7]-polyhedra via two bridging F?, resulting in [PdZrF11]-groups. These [PdZrF11]-groups built up a threedimensional-network with K+ in its spacings. KPdHfF7 crystallizes isotypically (a = 1 136.1(3) pm, b = 796.4(2) pm und c = 638.8(1) pm; four cycle diffractometer data, AED2).  相似文献   

14.
Journal of Solid State Electrochemistry - Li7La3Zr2O12 (LLZO) is one of the most competent candidates as a solid electrolyte for next-generation Li-ion batteries. Although the stabilization of the...  相似文献   

15.
低温水热合成是水热化学一个活跃的研究方向,在氧化物粉末的合成方面具有潜在的应用价值.La2M2O7(M=Ti,Zr)陶瓷材料的优良特性使其多晶粉末的合成倍受关注[1,2].  相似文献   

16.
Russian Journal of General Chemistry - The formation mechanisms for a series of n = 2 Ruddlesden-Popper phases Ln2SrFe2O7 (Ln = La, Nd, Gd, Dy) in the Ln2O3-SrO-Fe2O3 systems were determined. The...  相似文献   

17.
The photocatalytic activities of R3MO7 and R2Ti2O7 (R=Y, Gd, La; M=Nb, Ta) strongly depended on the crystal structure. Overall, photocatalytic water splitting into H2 and O2 proceeded over La3TaO7 and La3NbO7, which have an orthorhombic weberite structure, Y2Ti2O7 and Gd2Ti2O7, which have a cubic pyrochlore structure, and La2Ti2O7, which has a monoclinic perovskite structure. All of these materials are composed of a network of corner-shared octahedral units of metal cations (TaO6, NbO6, or TiO6); materials without such a network were inactive. The octahedral network certainly increased the mobility of electrons and holes, thereby enhancing photocatalytic activity.  相似文献   

18.
Hf2Ni2In, Hf2Ni2Sn, Hf2Cu2In, and Hf2Pd2In were synthesized by reacting the elements in an arc-melting furnace under argon and subsequent annealing at 970 K. They crystallize with an ordered Zr3Al2 type structure, space group P42/mnm which was refined from single crystal X-ray data for Hf2Ni2In (a = 713.9(1) pm, c = 660.4(2) pm, wR2 = 0.0665, 513 F2 values) and Hf2Ni2Sn (a = 703.1(1) pm, c = 676.1(2) pm, wR2 = 0.0423, 507 F2 values) with 18 parameters for each refinement. The lattice constants for Hf2Cu2In and Hf2Pd2In are a = 715.5(1) pm, c = 677.0(1) pm and a = 742.6(1) pm, c = 679.4(2) pm, respectively. The structures may be considered as an intergrowth of distorted CsCl- and AlB2-like slabs. Magnetic susceptibility measurements indicate Pauli paramagnetism for Hf2Ni2In and Hf2Ni2Sn, which is consistent with the metallic conductivity observed for Hf2Ni2In. 119Sn Mössbauer spectroscopy of Hf2Ni2Sn shows one signal with an isomer shift of δ = 1.59(1) mm/s subjected to quadrupole splitting of δEq = 0.81(1) mm/s.  相似文献   

19.
The solid lithium-ion electrolyte "Li(7)La(3)Zr(2)O(12)" (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, (6)Li and (7)Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24d Li site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy E(a) characterizing long-range ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 × 10(-4) Scm(-1) to 4 × 10(-4) Scm(-1) depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 × 10(-6) Scm(-1), E(a) = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb-Wagner polarization technique. The electronic transference number t(e-) is of the order of 10(-7). Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.  相似文献   

20.
Polymer–ceramic composite electrolytes are emerging as a promising solution to deliver high ionic conductivity, optimal mechanical properties, and good safety for developing high‐performance all‐solid‐state rechargeable batteries. Composite electrolytes have been prepared with cubic‐phase Li7La3Zr2O12 (LLZO) garnet and polyethylene oxide (PEO) and employed in symmetric lithium battery cells. By combining selective isotope labeling and high‐resolution solid‐state Li NMR, we are able to track Li ion pathways within LLZO‐PEO composite electrolytes by monitoring the replacement of 7Li in the composite electrolyte by 6Li from the 6Li metal electrodes during battery cycling. We have provided the first experimental evidence to show that Li ions favor the pathway through the LLZO ceramic phase instead of the PEO‐LLZO interface or PEO. This approach can be widely applied to study ion pathways in ionic conductors and to provide useful insights for developing composite materials for energy storage and harvesting.  相似文献   

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