Defect chemistry, surface structures, and lithium insertion in anatase TiO2

Atomistic simulation techniques are used to investigate the defect properties of anatase TiO(2) and Li(x)TiO(2) both in the bulk and at the surfaces. Interatomic potential parameters are derived that reproduce the lattice constants of anatase, and the energies of bulk defects and surface structures are calculated. Reduction of anatase involving interstitial Ti is found to be the most favorable defect reaction in the bulk, with a lower energy than either Frenkel or Schottky reactions. The binding energies of selected defect clusters are also presented: for the Ti(3+)-Li(+) defect cluster, the binding energy is found to be approximately 0.5 eV, suggesting that intercalated Li ions stabilize conduction band electrons. The Li ion migration path is found to run between octahedral sites, with an activation energy of 0.45-0.65 eV for mole fractions of lithium in Li(x)TiO(2) of x < or = 0.1. The calculated surface energies are used to predict the crystal morphology, which is found to be a truncated bipyramid in which only the (101) and (001) surfaces are expressed, in accord with the available microscopy data. Calculations of defect energies at the (101) surface suggest that single Ti(3+) defects and neutral Ti(3+)-Li(+) pairs tend to segregate to the surface.     

Lithium diffusion pathways and vacancy formation in the Pmmn-Li(1-x)FeO2 electrode material

Models for Li(+) ion mobility were developed and investigated in the 'corrugated layer' orthorhombic phase of Li(1-x)FeO(2), an attractive possible electrode material for reversible lithium ion batteries. The ground-state crystal energy was computed by first-principles DFT (Density-Functional-Theory) methods, based on the use of the hybrid B3LYP functional with localized Gaussian-type basis sets. Appropriate supercells were devised as needed, with full least-energy structure optimization. In the defect-free case (x = 0), ion diffusion was found to take place cooperatively inside a fraction of active lithium layers separated by inert ones, so as to reduce lattice strain; intermediate bottleneck states of Li are either in tetrahedral (energy barrier ΔE(a) = 0.410 eV) or linear (ΔE(a) = 0.468 eV) coordination. For the Li(0.75)FeO(2) deintercalated material a number of low energy vacancy configurations were considered, investigating also the vacancy influence on electron density of states and atomic charge distribution. The most favourable ion transport mechanisms (ΔE(a) = 0.292 and 0.304 eV) imply a linear Li bottleneck state, with all lithium layers active and a quite small lattice strain. Accordingly, in the defective material the predicted ionic conductivity at room temperature rises from 10(-5)-10(-6) (LiFeO(2)) to 4 × 10(-4) ohm(-1) cm(-1) (Li(0.75)FeO(2)).     

On the influence of the vacancy distribution on the structure and ionic conductivity of A-site-deficient Li(x)Sr(x)La(2/3-x)TiO3 perovskites

The crystal structure and dielectric properties of slowly cooled A-site-deficient perovskites Li(x)Sr(x)La(2/3-x)□(1/3-x)TiO(3) (0.04 ≤ x ≤ 0.33) have been investigated by powder X-ray diffraction (XRD), impedance spectroscopy, and (7)Li NMR techniques. In this series, nominal vacancies decrease with Li content, but the total amount of A-site vacancies, n(t) = Li + □, participating in conduction processes remains basically constant. Rietveld analysis of the XRD patterns showed a change of symmetry from orthorhombic to tetragonal when the lithium and strontium contents increased above x = 0.08 and from tetragonal to cubic above x = 0.16. Structural modifications are mainly due to the cation vacancy ordering along the c axis, which disappear gradually when the lithium content increases. In agreement with the structural information, two lithium signals with different quadrupole constants are detected in (7)Li NMR spectra of orthorhombic/tetragonal phases, which have been associated with lithium in two crystallographic z/c = 0 and 1/2 planes of perovskites. In cubic samples, only a single narrow component, indicative of mobile species, was detected. Lithium motion was thermally activated, with activation energies going from 0.35 to 0.38 eV. Evolution of the bulk dc-conductivity preexponential factors along the series showed a maximum that has been first related to the dependence of lithium hopping on the lithium and vacancy concentrations. Finally, changes in the vacancy ordering, produced along the series, affect the dimensionality of the conductivity, indicating that not only the amount of vacancies but also its distribution are relevant.     

The influence of size on phase morphology and Li-ion mobility in nanosized lithiated anatase TiO2

Sustainable energy storage in the form of Li-ion batteries requires new and advanced materials in particular with a higher power density. Nanostructuring appears to be a promising strategy, in which the higher power density in nanosized materials is related to the dramatically shortened Li-ion diffusion paths. However, nanosizing materials also changes intrinsic material properties, which influence both ionic and electronic conductivity. In this work neutron diffraction is used to show that in addition to these two aspects, nanostructuring changes the phase behavior and morphology. Lithiated 40-nm TiO(2) anatase crystallites become single phase, either having the Li-poor original anatase phase, or the Li-rich Li-titanate phase, in contrast to microsized crystallites where these two phases coexist in equilibrium within one crystal particle. In addition, Li(x)TiO(2) compositions occur with stoichiometries that are not stable in micron-sized crystallites, indicating enhanced solid solution behavior. Reduced conduction electron densities at the sites of the Li ions are observed by NMR spectroscopy. This is accompanied by reduced spontaneous Li-ion mobility, suggesting a correlation between the electron density at the Li-ion site and the Li-ion mobility. The present results show that in the case of lithiated anatase TiO(2), significant effects on phase composition, morphology, and electronic configurations are induced, as well as slower intracrystallite Li diffusion.     

Extremely slow Li ion dynamics in monoclinic Li(2)TiO(3)-probing macroscopic jump diffusion via(7)Li NMR stimulated echoes

A thorough understanding of ion dynamics in solids, which is a vital topic in modern materials and energy research, requires the investigation of diffusion properties on a preferably large dynamic range by complementary techniques. Here, a polycrystalline sample of Li(2)TiO(3) was used as a model substance to study Li motion by both (7)Li spin-alignment echo (SAE) nuclear magnetic resonance (NMR) and ac-conductivity measurements. Although the two methods do probe Li dynamics in quite different ways, good agreement was found so that the Li diffusion parameters, such as jump rates and the activation energy, could be precisely determined over a dynamic range of approximately eleven decades. For example, Li solid-state diffusion coefficients D(σ) deduced from impedance spectroscopy range from 10(-23) m(2) s(-1) to 10(-12) m(2) s(-1) (240-835 K). These values are in perfect agreement with the coefficients D(SAE) deduced from SAE NMR spectroscopy. As an example, D(SAE) = 2 × 10(-17) m(2) s(-1) at 433 K and the corresponding activation energy determined by NMR amounts to 0.77(2) eV (400-600 K). At room temperature D(σ) takes a value of 3 × 10(-21) m(2) s(-1).     

Evolution of structure, transport properties and magnetism in ternary lithium nitridometalates Li(3-x-y)M(x)N, M = Co, Ni, Cu

The structures, magnetism and ion transport properties of the ternary nitrides Li(3-x-y)M(x)N (M = Co, Ni, Cu; y= lithium vacancy) were examined by powder X-ray diffraction, solid-state NMR and SQUID magnetometry. Doping levels are achieved up to x approximately = 0.4 for M = Cu and Co, but much higher substitution levels (x approximately =1) are obtained in the Li-Ni-N system. Transition metals substitute for Li at the Li(1) interplanar site and the ensuing lithium vacancies are disordered within the [Li(2)N] planes. High substitution levels in the Li-Ni-N system lead to the formation of ordered phases. Diffusion parameters, including activation energies, correlation times and diffusion coefficients, were obtained from variable-temperature solid-state NMR measurements in several ternary compounds. SQUID magnetometry shows significant variations of the electronic properties with dopant and x. The properties of the ternary nitrides can be rationalised in terms of the identity of the dopant and the structural modifications arising from the substitution process.     

Theoretical study of adsorption of O((3)P) and H(2)O on the rutile TiO(2)(110) surface

The adsorption of oxygen atoms O(3P) on both ideal and hydrated rutile TiO(2)(110) surfaces is investigated by periodic density functional theory (DFT) calculations within the revised Perdew-Burke-Ernzerhof (RPBE) generalized gradient approximation and a four Ti-layer slab, with (2 x 1) and (3 x 1) surface unit cells. It is shown that upon adsorption on the TiO(2) surface the spin of the O atom is completely lost, leading to stable surface peroxide species on both in-plane and bridging oxygen sites with O-binding energies of about 1.0-1.5 eV, rather than to the kinetically unstable terminal Ti-O and terminal O-O species with smaller binding energies of 0.1-0.7 eV. Changes in O-atom coverage ratios between 1/3 and 1 molecular layer (ML) and coadsorption of H(2)O have only minor effects on the O-binding energies of the stable peroxide configurations. High O-atom diffusion barriers of about 1 eV are found, suggesting a slow recombination rate of adsorbed O atoms on TiO(2)(110). Our results suggest that the TiOOTi peroxide intermediate experimentally observed in photoelectrolysis of water should be interpreted as a single spinless O adatom on TiO(2) surface rather than as two Ti-O* radicals coupled together.     

Ionization potentials of small lithium clusters (Lin) and hydrogenated lithium clusters (LinH)

We present accurate ionization potentials (IPs) for small lithium clusters and hydrogenated lithium clusters (n=1-4), computed using coupled-cluster singles and doubles theory augmented with a perturbative correction for connected triple excitations [CCSD(T)] with the correlation-consistent weighted core-valence quadruple-zeta basis set (cc-pwCVQZ). In some cases the full CCSDT method has been used. Comparison of computed binding energies with experiment for the pure cationic lithium clusters reveals excellent agreement, demonstrating that previous discrepancies between computed and experimentally derived atomization energies for the corresponding neutral clusters are due to the use of an inaccurate experimental IP for Li(4). The experimental IP for Li(4) falls 0.43 eV below our theoretical adiabatic value of 4.74 eV, which should be a lower bound to the measured IP. Our recommended zero-point corrected adiabatic IPs for Li, Li(2), Li(3), Li(4), LiH, Li(2)H, Li(3)H, and Li(4)H are 5.39, 5.14, 4.11, 4.74, 7.69, 3.98, 4.69, and 4.05 eV, respectively. Zero-point vibrationally corrected CCSD(T) atomization energies per atom for Li(2) (+), Li(3) (+), Li(4) (+), LiH(+), Li(2)H(+), Li(3)H(+), and Li(4)H(+) are 0.64, 0.96, 0.90, 0.056, 1.62, 1.40, and 1.40 eV, respectively.     

Extensive migration of Ni and Mn by lithiation of ordered LiMg0.1Ni0.4Mn(1.5)O4 spinel

Li(x)Mg(0.1)Ni(0.4)Mn(1.5)O(4) spinel (P4(3)32) was chemically and electrochemically lithiated in the range 1 < x 相似文献   

Trapping of charge carriers in colloidal particles of self-assembled films from TiO(2) and poly(vinyl sulfonic acid)

Self-assembled electrodes consisting of TiO(2) nanoparticles and poly(vinyl sulfonic acid) (PVS) were prepared by the layer-by-layer (LbL) technique. The electrostatic interaction between the TiO(2) nanoparticles and PVS allowed the growth of visually uniform multilayers of the composite, with high control of the thickness and nanoarchitecture. The electrochemical and chromogenic properties of these TiO(2)/PVS films were examined in an electrolytic solution of 0.5 M LiClO(4)/propylene carbonate. The presence of two intercalation sites was noted during the positive potential scan, and they were attributed to different mobilities of charge carriers. Several charge/discharge cycles demonstrated the trapping of charge carriers in the TiO(2) sites. The absorbance change associated with the oxidation of the trapping sites was attributed to electronic transitions involving energy states in the gap band formed due to the strong distortion of the TiO(2) host. Using the quadratic logistic equation (QLE), it was possible to analyze the electronic intervalence transfer from Ti(3+) to Ti(4+). Using the parameters obtained from this fitting, the amount of trapping sites in the LbL film was also determined. Electrochemical impedance spectroscopy (EIS) data gave the time constant associated with diffusion and the trapping sites. The diffusion coefficient of lithium ions changed from ca. 4.5 x 10(-13) cm(2) s(-1) to 3.0 x 10(-14) cm(2) s(-1) for all the potential range applied, indicating that PVS did not hinder the ionic transport within the LbL film. Finally, on the basis of the spectroelectrochemical data and scanning electron micrographs, the trapping effects were attributed to the colloidal particles of Li(0.55)TiO(2).     

Density functional study of the interfacial electron transfer pathway for monolayer-adsorbed InN on the TiO(2) anatase (101) surface

Density functional theory (DFT) in connection with ultrasoft pseudopotential (USP) and generalized gradient spin-polarized approximations (GGSA) is applied to calculate the adsorption energies and structures of monolayer-adsorbed InN on the TiO(2) anatase (101) surface and the corresponding electronic properties, that is, partial density of states (PDOS) for surface and bulk layers of the TiO(2) anatase (101) surface and monolayer-adsorbed InN, to shed light on the possible structural modes for initial photoexcitation within the UV/vis adsorption region followed by fast electron injection through the InN/TiO(2) interface for an InN/TiO(2)-based solar cell design. Our calculated adsorption energies found that the two most probable stable structural modes of monolayer-adsorbed InN on the TiO(2) anatase (101) surface are (1) an end-on structure with an adsorption energy of 2.52 eV through N binding to surface 2-fold coordinated O (O(cn2)), that is, InN-O(cn2), and (2) a side-on structure with an adsorption energy of 3.05 eV through both N binding to surface 5-fold coordinated Ti (Ti(cn5)) and In bridging two surface O(cn2), that is, (O(cn2))(2)-InN-Ti(cn5). Our calculated band gaps for both InN-O(cn2) and (O(cn2))2-InN-Ti(cn5) (including a 1.0-eV correction using a scissor operator) of monolayer-adsorbed InN on the TiO(2) anatase (101) surface are red-shifted to 1.7 eV (730 nm) and 2.3 eV (540 nm), respectively, which are within the UV/vis adsorption region similar to Gratzel's black dye solar cell. Our analyses of calculated PDOS for both surface and bulk layers of the TiO(2) anatase (101) surface and monolayer-adsorbed InN on the TiO(2) anatase (101) surface suggest that the (O(cn2))(2)-InN-Ti(n5) configuration of monolayer-adsorbed InN on the TiO(2) anatase (101) surface would provide a more feasible structural mode for the electron injection through the InN/TiO(2) interface. This is due to the presence of both occupied and unoccupied electronic states for monolayer-adsorbed InN within the band gap TiO(2) anatase (101) surface, which will allow the photoexcitation within the UV/vis adsorption region to take place effectively, and subsequently the photoexcited electronic states will overlap with the unoccupied electronic states around the lowest conduction band of the TiO(2) anatase (101) surface, which will ensure the electron injection through the InN/TiO(2) interface. Finally, another thing worth our attention is our preliminary study of double-layer-adsorbed InN on the TiO(2) anatase (101) surface, that is, (O(cn2))(2)-(InN)(2)-Ti(cn5), with a calculated band gap red-shifted to 2.6 eV (477 nm) and a different overlap of electronic states between double-layer-adsorbed InN and the TiO(2) anatase (101) surface qualitatively indicated that there is an effect of the thickness of adsorbed InN on the TiO(2) anatase (101) surface on both photoexcitation and electron injection processes involved in the photoinduced interfacial electron transfer through InN/TiO(2). A more thorough and comprehensive study of different layers of InN adsorbed in all possible different orientations on the TiO(2) anatase (101) surface is presently in progress.     

Density functional theory study of formic acid adsorption on anatase TiO2(001): geometries, energetics, and effects of coverage, hydration, and reconstruction

We present density functional theory calculations and first-principles molecular dynamics simulations of formic acid adsorption on anatase TiO(2)(001), the minority surface exposed by anatase TiO(2) nanoparticles. A wide range of factors that may affect formic acid adsorption, such as coverage, surface hydration, and reconstruction, are considered. It is found that (i) formic acid dissociates spontaneously on unreconstructed clean TiO(2)(001)-1 x 1, as well as on the highly reactive ridge of the reconstructed TiO(2)(001)-1 x 4 surface; (ii) on both the 1 x 1 and 1 x 4 surfaces, various configurations of dissociated formic acid exist with adsorption energies of about 1.5 eV, which very weakly depend on the coverage; (iii) bidentate adsorption configurations, in which the formate moiety binds to the surface through two Ti-O bonds, are energetically more favored than monodentate ones; (iv) partial hydration of TiO(2)(001)-1 x 1 tends to favor the bidentate chelating configuration with respect to the bridging one but has otherwise little effect on the adsorption energetics; and (v) physical adsorption of formic acid on fully hydrated TiO(2)(001)-1 x 1 is also fairly strong. Comparison of the present results for formic acid adsorption with those for water and methanol under similar conditions provides valuable insights to the understanding of recent experimental results concerning the coadsorption of these molecules.     

Spinel-to-CaFe2O4-type structural transformation in LiMn2O4 under high pressure

A new form of LiMn2O4 is reported. The structure is the CaFe2O4-type and 6% denser than the spinel. The structure transformation was achieved by heating at 6 GPa. Analysis of the neutron diffraction pattern confirmed an average of the structure; the unit cell was orthorhombic at a = 8.8336(5) angstroms, b = 2.83387(18) angstroms, and c = 10.6535(7) angstroms (Pnma). Electron diffraction patterns indicated an order of superstructure 3a x b x c, which might be initiated by Li vacancies. The exact composition is estimated at Li(0.92)Mn2O4 from the structure analysis and quantity of intercalated Li. The polycrystalline CaFe2O4-type compound showed semiconducting-like characters over the studied range above 5 K. The activation energy was reduced to approximately 0.27 eV from approximately 0.40 eV at the spinel form, suggesting a possible enhancement of hopping mobility. Magnetic and specific-heat data indicated a magnetically glassy transition at approximately 10 K. As the CaFe2O4-type transition was observed for the mineral MgAl2O4, hence the new form of the lithium manganese oxide would provide valuable opportunities to study not only the magnetism of strongly correlated electrons but also the thermodynamics of the phase transition in the mantle.     

由钛酸盐纳米带水热制备锐钛矿型TiO2纳米带

研究了水热处理具有层状结构的钛酸钠纳米带或钛酸纳米带转化为锐钛矿型TiO₂的制备过程、难易程度和相转化机理. 实验结果表明, 当水热反应温度和时间分别在160 ℃ 和24 h以内, 钛酸钠纳米带很难完全转化为锐钛矿型TiO₂, 若升高反应温度并延长反应时间, 则可制得纯的锐钛矿型TiO₂, 但纳米带形貌被严重破坏; 当水热反应温度和时间分别为160 ℃ 和16 h时, 1次酸洗的钛酸纳米带能够完全转化为锐钛矿型TiO₂, 若钛酸纳米带经过3次强酸浸泡, 则在160 ℃下相转化时间就会缩短到12 h, 所有钛酸纳米带在转化为TiO₂后的形貌仍为纳米带, 但经3次酸浸后生成的TiO₂纳米带表面更光滑. 讨论了钛酸钠纳米带或钛酸纳米带转化为锐钛矿型TiO₂的相转化机理.     

S(1S) production following electron impact on thiophosgene (Cl2CS)

A special xenon matrix detector has been used to study the production of S(1S) following controlled electron impact on thiophosgene (Cl2CS) targets over an electron energy range from threshold to 400 eV. Time-of-flight spectroscopy has been used to measure S(1S) fragment kinetic energies. Fragments with energies in excess of 1 eV have been observed. The absolute cross section for S(1S) production reaches a maximum of [1.05+/-0.35] x 10(-18) cm2 at approximately 125 eV impact energy. Two different fragmentation processes, involving triplet and singlet excited states of the parent Cl2CS molecule, have been identified.     

水热法合成高功率锂离子二次电池用球形Li4Ti5O12负极材料

以球形TiO2和LiOH溶液为反应物,通过水热法合成了尖晶石型Li4Ti5O12,并使用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、扫描电镜(SEM)和激光粒度分布(PSD)对其结构、形貌和电化学性能进行了表征.结果表明:通过该法得到的产品颗粒大小均匀,粒度分布狭窄,结构与标准Li4Ti5O12谱图一致.实验选定温度下所得的Li4Ti5O12均表现出良好的电化学性能.其中,800°C热处理所得样品的电化学性能最好,室温下,以35mA·g-1的电流密度进行充放电,其可逆容量达到162mAh·g-1,同时这种材料也表现出良好的倍率性能,即使在720mA·g-1的电流密度条件下进行充放电,其可逆容量仍可达到124mAh·g-1.     

Cation mobility and kinetics of ion exchange in zirconium hydrogen monothiophosphate hydrate, Zr(HPO(3)S)(2)x1.5H(2)O

The ion conductivity of zirconium hydrogen monothiophosphate (Zr(HPO(3)S)(2)x1.5H(2)O) has been measured by impedance spectroscopy. The measured value of proton conductivity is 3 x 10(-5) S/cm at 298 K. Conductivity was shown to decrease with increasing temperature due to a dehydration process. Above 450 K, the conductivity is likely governed by proton transport in the anhydrous phase Zr(HPO(3)S)(2). The activation energies of proton conductivity were measured to be 18 +/- 2 kJ/mol for Zr(HPO(3)S)(2)x1.5H(2)O and 60 +/- 3 kJ/mol for the anhydrous compound. The kinetics of ion exchange was studied with the use of potentiometric titration for several ion pairs, H(+)/Na(+), H(+)/Zn(2+), and Na(+)/Zn(2+) in Zr(HPO(3)S)(2)x1.5H(2)O. The diffusion coefficient values for H(+)/Na(+) ion exchange in Zr(HPO(3)S)(2)x1.5H(2)O are lower than those reported in alpha-zirconium phosphate. At the same time, the mobility of zinc ions in Zr(HPO(3)S)(2)x1.5H(2)O is higher than sodium ion mobility. The ion exchange H(+)/Zn(2+) is accompanied by the slow hydrolysis of the initial compound. In all cases, the powdered solids were evaluated by powder X-ray diffraction, and particle sizes were controlled by grinding and sieving the powders.     

Anomalous ionic conductivity increase in Li2S + GeS2 + GeO2 glasses

Numerous studies of the ionic conductivities in oxide-doped chalcogenaide glasses have shown the anomalous result that the ionic conductivity actually increases significantly (by more than a factor of 10 in some cases) by the initial addition of an oxide phase to a pure sulfide glass. After this initial sharp increase, the conductivity then monotonically decreases with further oxide addition. While this behavior is important to the application of these glasses for Li batteries, no definitive understanding of this behavior has been elucidated. To examine this effect further and more completely, the ionic conductivities of 0.5Li(2)S + 0.5[(1 - x)GeS(2) + xGeO(2)] glasses have been measured on disc-type bulk glasses. The ionic conductivity of the 0.5Li(2)S + 0.5GeS(2) (x = 0) glass was observed to increase from 4.3 x 10(-5) (Omega cm)(-1) to 1.5 x 10(-4) (Omega cm)(-1) while the activation energy decreased to 0.358 eV from 0.385 eV by the addition of 5 mol % of GeO(2). Further addition of GeO(2) monotonically decreased the conductivity and increased the activation energy. On the basis of our previous studies of the structure of this glass system, the Anderson and Stuart model was applied to explain the decrease in the activation energy and increase in the conductivity. It is suggested that the "doorway" radius between adjacent cation sites increases slightly (from approximately 0.29(+/-0.05) A to approximately 0.40(+/-0.05) A) with the addition of oxygen to the glass and is proposed to be the major cause in decreasing the activation energy and thereby increasing the conductivity. Further addition of oxides appears to contract the glass structure (and the doorway radius) leading to an increase in the conductivity activation energy and a decrease in the conductivity.     

Ultraslow Li diffusion in spinel-type structured Li4Ti5O12 - a comparison of results from solid state NMR and impedance spectroscopy

The cubic spinel oxides Li(1+x)Ti(2-x)O(4) (0 < or =x< or = 1/3) are promising anode materials for lithium-ion rechargeable batteries. The end member of the Li-Ti-O series, Li(4)Ti(5)O(12), can accommodate Li ions up to the composition Li(7)Ti(5)O(12). Whereas a number of studies focus on the electrochemical behaviour of Li insertion into and Li diffusion in the Li intercalated material, only few investigations about low-temperature Li dynamics in the non-intercalated host material Li(4)Ti(5)O(12) have been reported so far. In the present paper, Li diffusion in pure-phase microcrystalline Li(4)Ti(5)O(12) with an average particle size in the microm range was probed by (7)Li solid state NMR spectroscopy using spin-alignment echo (SAE) and spin-lattice relaxation (SLR) measurements. Between T = 295 K and 400 K extremely slow Li jump rates tau(-1) ranging from 1 s(-1) to about 2200 s(-1) were directly measured by recording the decay of spin-alignment echoes as a function of mixing time and constant evolution time. The results point out the slow Li diffusion in non-intercalated Li(4)Ti(5)O(12) x tau(-1) (1/T) follows Arrhenius behaviour with an activation energy E(ASAE) of about 0.86 eV. Interestingly, E(ASAE) is comparable to activation energies deduced from conductivity measurements (0.94(1) eV) and from SLR measurements in the rotating frame (0.74(2) eV) rather than from those performed in the laboratory frame, E(A)(low-T) = 0.26(1) eV at low T.     

Multiple Li positions inside oxygen octahedra in lithiated TiO2 anatase

Intercalation of Li in TiO2 anatase results in a phase separation in a Li-poor and a Li-rich phase. The local lithium configuration in the coexisting crystallographic phases is resolved by detailed analysis of neutron diffraction data. In each of the phases, two distinct positions within the octahedral interstices are found, with a temperature-dependent occupancy. A combination of quasi-elastic neutron scattering and force field molecular dynamics simulations shows that Li is hopping on a picosecond time scale between the two sites in the octahedral interstices. The results also suggest a specific Li arrangement along the crystallographic a direction, albeit without long range order. It is likely that multiple discrete Li sites within a distorted oxygen octahedron occur not only in intercalated TiO2 anatase but also in other (transition metal) oxides.