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1.
The La ordering and domain structures of La2/3 ? xLi3xTiO3 single crystals and quenched samples have been observed by high resolution electron microscopy. In single crystals, the grown single crystals are not real single crystals with mono-domain, but crystals with 90° oriented domains with 20–100 nm sizes. A remarkable difference of the domain size between polycrystals and single crystals has not been observed at the same composition. In quenched samples, the La disordering has been observed. Furthermore, domain structures of quenched samples are different from those of furnace-cooled ones. Domain structures change with the La disordering. The understanding of microstructures is necessary to clarify the Li-ion conduction mechanism.  相似文献   

2.
《Solid State Ionics》2006,177(35-36):3037-3044
The average structure and microstructure of a lithium-ion conducting perovskite La2/3−xLi3xTiO3 (x = 0.12) were investigated using neutron diffraction and transmission electron microscopy (TEM). The obtained results were compared with those of previous studies on La2/3−xLi3xTiO3 series compounds, and the relationship between their structures and ionic conduction was discussed. The Rietveld refinement using neutron diffraction data reveals that the average structure (space group: Cmmm) of furnace-cooled Li-rich La2/3−xLi3xTiO3 (x = 0.12) involves alternative ordered arrangement of La along the c-axis and anti-phase-tilt of TiO6 octahedra along the b-axis as with Li-poor La2/3−xLi3xTiO3(x = 0.05). It was found that the strong correlation between structure and percolative diffusion pathways in the perovskites is primarily referred to the ordered arrangement of La ions, and the “bottleneck” square—surrounded by four oxygen ions determined by the distortion and tilt of TiO6 octahedra. In addition, the 90°-oriented micro-domain structure, which also influences the percolative diffusion pathways in La2/3−xLi3xTiO3, was observed by TEM.  相似文献   

3.
TiO2-coated sericite powders were prepared by the chemical deposition method starting from lamellar sericite and TiCl4 in the presence or absence of La3+ cations. After calcination at 900 °C for 1 h, the resultant TiO2 nanoparticles on the sericite surfaces existed in anatase phase. The light scattering indexes of the TiO2-coated lamellar sericite powders were dozens of times higher than that of the naked lamellar sericite powders. The presence of La3+ in the deposition solution was beneficial to the formation of the small-sized anatase TiO2 nanoparticles, resulting in the formation of the dense and uniform island-like TiO2 coating layers in a large range of the weight ratios of TiO2 to sericite from 5% to 20%. The TiO2-coated lamellar sericite powders prepared in the presence of La3+ had higher light scattering index than that prepared in the absence of La3+. XPS analysis shows that when La3+ cations were absent in the reaction solution, TiO2 coating layers anchored at the sericite surface via the Ti-O-Si and Ti-O-Al bonds. The presence of La3+ cations caused the formation of Si-O-La and Al-O-La bonds at the sericite surface and Ti-O-La bond at the surface of TiO2 coating layers. After coating TiO2 on the sericite surface, the yellowness of the TiO2-coated sericite powders obviously increased and the brightness slightly decreased.  相似文献   

4.
W.G. Wang  X.P. Wang  Y.X. Gao  Q.F. Fang 《Solid State Ionics》2009,180(23-25):1252-1256
The electrical properties and the mechanism of lithium ionic diffusion in the Li7La3Ta2O13 compounds were investigated. The bulk and total conductivity at 300 K of the Li7La3Ta2O13 compound are about 3.3 × 10? 6 S/cm and 2.6 × 10? 6 S/cm, respectively. The activation energy of bulk and total conductivity is in the range of 0.38–0.4 eV. A prominent internal friction peak in Li7La3Ta2O13 compounds was observed around 280 K at 0.5 Hz, which is actually composed of two subpeaks (P1 peak at lower temperature and P2 peak at higher temperature). From the shift of peak position with frequency, the activation energy of 1.0 eV and the pre-exponential factor of relaxation time in the order of 10? 18–10? 21 s were obtained if one assumes Debye relaxation processes. These values of relaxation parameters strongly suggest the existence of interaction between the relaxation species (here lithium ions or vacancies). Based on the coupling model, the relaxation activation energies are deduced as 0.45 eV and the pre-exponential factor of relaxation time as 10? 15 s. Judging from these relaxation parameters and the similarity of structure between Li7La3Ta2O13 and Li5La3Ta2O12 compounds, the P1 and P2 peaks are suggested to be related with the lithium ionic diffusion between 48g?48g and 24d?48g.  相似文献   

5.
Nanocrystalline Li2TiO3 was successfully synthesized using solid-state reaction method. The microstructural and electrochemical properties of the prepared material are systematically characterized. The X-ray diffraction pattern of the prepared material exhibits predominant (002) orientation related to the monoclinic structure with C2/c space group. HRTEM images and SAED analysis reveal the well-developed nanostructured particles with average size of ~40 nm. The electrochemical properties of the prepared sample are carried out using cyclic voltammetry (CV) and chronopotentiometry (CP) using Pt//Li2TiO3 cell in 1 mol L?1 Li2SO4 aqueous electrolyte. The Li2TiO3 electrode exhibits a specific discharge capacity of 122 mAh g?1; it can be used as anode in Li battery within the potential window 0.0–1.0 V, while investigated as a supercapacitor electrode, it delivers a specific capacitance of 317 F g?1 at a current density of 1 mA g?1 within the potential range ?0.4 to +0.4 V. The demonstration of both anodic and supercapacitor behavior concludes that the nanocrystalline Li2TiO3 is a suitable electrode material for supercapattery application.  相似文献   

6.
x La2/3+yTiO3-δ perovskite (with δ≤0.5) were deposited by the laser ablation technique from Li0.33La0.56TiO3 targets. Their growth onto MgO substrateswas studied as a function of the oxygen pressure. For films grown in vacuum (10-6 mbar), a La0.63TiO2.5 composition was obtained, meaning that Ti3+ alone is present in the films, while Li ions are not incorporated under these conditions. This material shows good electric conductivity (ρ=500 mΩ cm). By contrast, insulating films with a Li0.1La0.70TiO3 composition corresponding to the Ti4+ species were obtained at high oxygen pressures (>0.05 mbar). For all conditions, textured films were grown with different orientations depending on the temperature and the oxygen pressure. Received: 10 September 1997/Accepted: 24 November 1997  相似文献   

7.
(001)La0.67Sr0.33MnO3/(001)(BaxSr1 ? x TiO3/(001)La0.67Sr0.33MnO3(x= 0–0.25) three-layer heterostructures are grown by laser evaporation on (001)La0.3Sr0.7Al0.65Ta0.35O3 single-crystalline substrates. In a wide temperature range (≈150 K), effective permittivity ? of (1000 nm)Ba0.25Sr0.75TiO3 and (1000 nm)SrTiO3 films grown obeys the relationship ? ~ (T ? T CW)?1, where T CW is the Curie-Weiss temperature for related bulk crystals. Using experimental dependences ?(T), the capacitance of the (001)La0.67Sr0.33MnO3/(001)BaxSr1?x TiO3 and (001)La0.67Sr0.33MnO3/(001)SrTiO3 interfaces, which is due to electric field penetration into the manganite electrode, is estimated (C int≈4μF/cm2). At bias voltages of ± 2.5 V, the change in the permittivity of the STO and BSTO films in the heterostructures studied reaches 25 and 45%, respectively.  相似文献   

8.
The results of investigation into nanocrystalline lanthanum manganites La0.7Mn1.3O3 ± Δ produced by repeated cold isostatic pressing of a charge material are reported. A powder compact with a crystallite size of 5–7 nm exhibits no magnetic properties, unlike a coarse-grained (20 nm) powder compact.  相似文献   

9.
Ronghua Li  Liyun Zi  Chunzhi Shen  Wenji Wang 《Ionics》2005,11(1-2):146-151
The B-site substituted perovskite solid solution systems Li3xLa0.67−xREyTi1−2yPyO3 (RE=Sc, Y, Nd, Sm, Eu, Yb) have been investigated. Perovskite solid solutions formed in the range of x=0.10, y<0.10 for RE=Sc3+, Y3+, Yb3+, x=0.10, y≤0.05 for RE=Nd3+, Sm3+, Eu3+. Li0.3La0.57Nd0.05Ti0.9P0.05O3 has the highest bulk conductivity of 4.31×10−4 S·cm−1 and the highest total conductivity of 2.52×10−4 S·cm−1 at room temperature in all prepared compositions. The compositions have low activation energies of about 24–30 kJ/mol in the temperature ranges of 298–523 K. SEM studies showed that the sample made by solid-state reaction has a sphere-like morphology and a rough particle with particle size of about 50 μm. The research results also indicated that the reaction temperature decreases and the electrochemical stabilities of the titanate-based perovskite-type solid solutions are improved by using RE3+ and P5+ replaced Ti4+ on B-site in the Li3xLa0.67−xTiO3 parent.  相似文献   

10.
H. Y. Liu  W. J. Wang  G. R. Liu 《Ionics》2001,7(3):229-231
Lithium ion conductors of the overall composition LixLa2/3Ti1−xPxO3+x (hereafter referred to as LTP) based on La2/3TiO3 were prepared by solid state reaction at high temperature (1300 °C). AC impedance measurements indicate that the total conductivities are of the order of 10−4 S·cm−1 when x=0.28 − 0.35 at room temperature and have an activation energy of 18 kJ·mol−1 in the temperature range from room temperature to 400 °C. X-ray powder diffraction patterns showed that the LTP system has a complex composition, which contains the solid solution perovskite Li3xLa2/3−xTiO3 and LaPO4.  相似文献   

11.
H. Y. Liu  W. J. Wang  S. T. Wu 《Ionics》2002,8(3-4):278-280
Lithium fast ion conductors of the composition Li0.3La2/3Ti0.7P0.3−xVxO3.3 (LTV) based on mixtures of Li3xLa2/3−xTiO3 and LaPO4 were prepared by solid state reaction at high temperature (≈ 1300 °C). AC impedance measurements indicate total conductivities of about 1 × 10−4 Scm−1 for compositions of x=0∼0.3 at room temperature with an activation energy of ≈18 kJ·mol−1 in the temperature range from 30 to 400 °C. X-ray powder diffraction patterns showed that the LTV system is composed of Li3xLa2/3−xTiO3 perovskite solid solution and LaP1−xVxO4 solid solution.  相似文献   

12.
Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO2 structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2. Indeed, Li[Ni0.50Mn0.50]O2 compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni0.17Li0.22Mn0.61]O2 and Li[Ni0.25Li0.17Mn0.58]O2 compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni2+ and about Ni3+, while the oxidation state of Mn ion sustains Mn4+ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2, in which Ni ion changes between Ni2+ and NI4+. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process.  相似文献   

13.
A microwave method has been developed for the preparation and sintering of lithium lanthanum titanate (LLTO) of the formula Li0.35La0.55TiO3. The method is fast, clean, economical and gives phase pure product of high conductivity.  相似文献   

14.
Y. Zou  N. Inoue  K. Ohara  V. Thangaduri  W. Weppner 《Ionics》2004,10(5-6):463-468
The Al-substitution effect was studied in solid solutions La4/3-yLi3y2/3-2yTi2O6 (LLTO). The ionic conductivity strongly depended on the Al concentration. The crystal structure, lattice parameters, ions occupation and bottleneck size were obtained by Rietveld analysis. Finally, the ionic conduction mechanism was discussed from the viewpoint of crystallographic factors.  相似文献   

15.
《Solid State Ionics》2006,177(19-25):1961-1964
Dense La0.6Sr0.4CoO3−δ film electrodes were deposited by pulsed laser deposition (PLD) on Ce0.9Gd0.1O1.95 electrolytes. The grain size of one film was 300–500 nm, and the other was 30–50 nm. DC polarization and AC impedance measurements were performed at 873 K–1073 K in O2–Ar gas mixtures. From investigations of the electrochemical capacitances, the rate determining process for both electrodes were confirmed to be the surface reaction. The analyses in the electrochemical resistance revealed that the oxygen adsorption/desorption rate was faster on the electrode with smaller grain size. DC responses agreed with AC results, so the current density on the nano-grain electrode was larger by half an order than those of the sub-micron-grain electrode. Under a dilute oxygen atmosphere, the rate determining step transferred from a surface reaction to a gas phase diffusion.  相似文献   

16.
An Al85Ni10La5 amorphous alloy, produced via gas atomization, was selected to study the mechanisms of nanocrystallization induced by thermal exposure. High resolution transmission electron microscopy results indicated the presence of quenched-in Al nuclei in the amorphous matrix of the atomized powder. However, a eutectic-like reaction, which involved the formation of the Al, Al11La3, and Al3Ni phases, was recorded in the first crystallization event (263°C) during differential scanning calorimetry continuous heating. Isothermal annealing experiments conducted below 263°C revealed that the formation of single fcc-Al phase occurred at 235°C. At higher temperatures, growth of the Al crystals occurred with formation of intermetallic phases, leading to a eutectic-like transformation behaviour at 263°C. During the first crystallization stage, nanocrystals were developed in the size range of 5 ~ 30 nm. During the second crystallization event (283°C), a bimodal size distribution of nanocrystals was formed with the smaller size in the range of around 10 ~ 30 nm and the larger size around 100 nm. The influence of pre-existing quenched-in Al nuclei on the microstructural evolution in the amorphous Al85Ni10La5 alloy is discussed and the effect of the microstructural evolution on the hardening behaviour is described in detail.  相似文献   

17.
Precisely (100)-oriented, 200-nm thick La0.67Ca0.33MnO3 films have been grown by laser ablation on a sapphire (R-plane) substrate covered by a (100)SrTiO3/(001)Bi2SrNb2O9/(001)CeO2 trilayer buffer. The azimuthal misorientation of crystal grains (50–300 nm) in the La0.67Ca0.33MnO3 films decreased by about 40% as the condensation temperature was increased ered from 760 to 810° C. The lattice parameter of the grown manganate films was reduced to 3.81–3.82 Å by enriching them with oxygen. The maximum in the temperature dependence of the electrical resistivity of the La0.67Ca0.33MnO3 films grown was shifted toward lower temperatures by 20–50 K relative to its position for bulk ceramic samples of a stoichiometric composition. The largest magnetoresistance (MR=42% at H=0.4 T) was found in La0.67Ca0.33MnO3 films with a Mn4+ concentration on the order of 50% (T=166 K).  相似文献   

18.
The La2/3Ca1/3MnO3 films 25-nm thick biaxially compressed in the substrate plane, grown quasi-coherently on the (001) surface of the LaAlO3 single crystal, were studied using laser vaporization. It was found that mechanical stresses acting during nucleation and growth promoted calcium enrichment of the cation sublattice of the manganite layer, which caused a decrease in its unit cell volume. Crystalline grains in manganite films were distinctly oriented along the normal to the substrate plane; the grain size in the substrate plane was within 20–40 nm, and the relative grain misorientation in the substrate plane did not exceed 0.2°. In zero magnetic field, the maximum in the temperature dependence of the resistivity ρ of La2/3Ca1/3MnO3 films was observed at temperatures close to 210 K. At T < 100 K and μ0 H = 2 T, the magnetoresistance of manganite films was negative, weakly depended on temperature, its value was about–0.45. The magnetic field caused transformation of nonferromagnetic phase inclusions to ferromagnetic ones, which resulted in a decrease in the La2/3Ca1/3MnO3 film resistivity with increasing magnetic field. At low temperatures (T < 100 K), a hysteresis was observed in the dependences of the film resistivity on the magnetic field.  相似文献   

19.
Microstructure and dielectric properties of Li2CO3 doped 0.7(Ba,Sr)TiO3–0.3MgO ceramics for the low temperature sintering and microwave applications will be presented. In these days, low temperature sintering process has been widely spread out for the integrated electronic modules for the communication systems such as front-end modules, antenna modules, and switching modules. We have added Li2CO3 and MgO to (Ba,Sr)TiO3 material to reduce the sintering temperature and improve dielectric properties such as loss tangent, and frequency dispersion.In this paper, we have discussed the crystalline properties, dielectric properties, and the microstructures of Li2CO3 doped 0.7(Ba,Sr)TiO3–0.3MgO ceramics. No pyro phase was observed in the X-ray diffraction method. Very weak frequency dispersion (<0.7%) of dielectric permittivity was observed from the 1 kHz to 1 MHz range. We found that the grain size of BST is around 2 μm, while the grain size of Li2CO3 dope 0.7BST–0.3MgO is around 4 μm from the SEM analysis.  相似文献   

20.
《Solid State Ionics》1999,116(3-4):263-269
New lithium ion conductors of perovskite-type compounds R1/4Li1/4TaO3 (R=La, Nd, Sm and Y) were synthesized, and their crystal structure and lithium ion conductivity were characterized. Symmetry of the perovskite lattice changed from cubic for La1/4Li1/4TaO3 to tetragonal for Nd1/4Li1/4TaO3 and Sm1/4Li1/4TaO3, and to orthorhombic for Y1/4Li1/4TaO3. The alternate ordering of R and Li ions and vacancies at the A-sites was observed for Nd1/4Li1/4TaO3, Sm1/4Li1/4TaO3 and Y1/4Li1/4TaO3. The cube root (V1/3) of the subcell volume decreased with decreasing the ionic radius of R cations which act as spacers for the perovskite lattice. With decrease in V1/3 from La1/4Li1/4TaO3 to Y1/4Li1/4TaO3, the bulk conductivity at 400 K decreased from 1.4×10−1 S m−1 to 5.0×10−7 S m−1 and its activation energy increased from 0.35 eV to 0.85 eV. The subcell volume and the ordering at the A-sites are major factors in influencing lithium ion conduction in these perovskite-type conductors.  相似文献   

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