N. Inoue

Structure and lithium ionic conduction mechanism in La4/3-yLi3yTi2O6

The solid solutions La4/3−yLi3yTi2O6 (y=0.09∼0.33) have been studied by complex impedance spectroscopy, X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) methods. The ionic conductivity shows a maximum value at around y=0.21, and keeps high values at high y concentrations. The XRD patterns show a single phase for all concentration. The crystal structure is orthorhombic with space groupPmmm for y=0.09∼0.15 and tetragonal with space groupP4/mmm for y=0.17∼0.33. The7Li static NMR spectra show a main central peak with a Lorenzian shape for y=0.09∼0.21. The central peak is divided into two parts for y=0.23∼0.33. The narrow intense peak is a mobile component due to mobile ions, and a small broad central peak is due to less mobile lithium ions which contribute to immobile component. The7Li MAS NMR spectra show negative chemical shifts which decrease with increasing y concentration. In this paper, we discuss the conduction mechanism and the structure from the analysis of conductivity, lattice parameters, occupation, atomic positions and the7Li static/MAS NMR spectra.

Structural disorder in lithium lanthanum titanate: the basis of superionic conduction

High-energy x-ray and neutron diffraction measurements on polycrystalline La(2/3-x)Li(3x)TiO(3) (0.075 < x < 0.165) were performed. The total scattering structure factors were analysed by the reverse Monte Carlo (RMC) modelling technique, resulting in three-dimensional particle configurations. These configurations were then used for revealing the distributions of La and Li ions and to understand the relationship between these distributions and ionic conduction. An alternating arrangement of La-rich and La-poor layers along the c-axis was found in the x = 0.075 composition. Intriguingly, this arrangement has gradually disappeared in samples with higher Li concentration. Furthermore, RMC models exhibit disordered distributions of Li ions, situated mainly on the La-rich layer, and there is a significant probability of Li ions occupying the interstitial sites (T site) between the O-3 triangle plane of the TiO(6) octahedron and an La ion or its vacancy site. It was also found on the basis of the RMC models that the bond valence sum (BVS) for Li ions behaves differently on La-rich and La-poor layers at low Li concentration compositions, but they are similar at high Li concentration compositions. This is consistent with the behaviour of the alternating arrangement of La-rich and La-poor layers. It is also suggested that the Li ions around the bottleneck at (1/2, 0, 0) (bottom layer) can jump to an adjacent bottleneck at (0, 1/2, 0) through the T site and not only Li ions in the La-poor layers but also Li ions in the La-rich layers contribute to the bottleneck-bottleneck Li conduction.

Stochastic effect in grazing ion surface scattering

Abstract The energy distribution of scattered ions is determined by the trajectory and the stochastic effect. In this paper, we discuss the stochastic effect, which originates from the stochastic nature of electronic excitations, and derive a simple relation between the energy loss and the energy straggling associated with the stochastic effect (stochastic energy straggling). For the Firsov model of the inelastic energy loss, the stochastic energy straggling can be calculated directly from the magnitude of the energy loss. We also discuss the ratio of the stochastic to the trajectory energy straggling obtained from recent experiments.

Structure and lithium ionic conduction of B-site Al-ion substitution in La4/3-yLi3yTi2O6

The Al-substitution effect was studied in solid solutions La4/3-yLi3y□2/3-2yTi2O6 (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.

Study of the trajectory effect in grazing ion surface scattering

Abstract The energy distribution observed in ion scattering experiments is determined by two effects. One is the trajectory effect and the other is the stochastic effect. The trajectory effect has been studied quantitatively by means of computer simulations written for low energy Ar beams scattered off an ideal Cu(111) surface. The stochastic effect is briefly discussed within the Firsov model. The present study shows that both the energy loss and the energy straggling are proportional to the primary beam energy and that the stochastic effect is larger than the trajectory effect.

Ionic conduction and chemical bonds of Li ion in La4/3−yLi3yTi2O6

The electronic state of La4/3−yLi3yTi2O6 (y=0.21) was studied by the DV-Xα cluster method. Four model clusters were used to calculate the density of state (DOS), the bond overlap population (BOP) and the net charge (NC). A Li ion in the model cluster was moved from 1b site to another 1b site along the x axis, and the BOP and the NC calculated were discussed. Furthermore, we calculated the potential energy with the movement of the Li ion along the x axis.

Electrical impedance and ultrasonic velocity of sodium ionic conductor Na1+2xZr2−xMgx(PO4)3

Abstract In the complex impedance representation, we observed either one or two semicircles strongly dependent on x, and a transition from one semicircle to two semicircles at x=0.4. Ultrasonic velocity showed an anomaly at x=0.4. Owing to this fact, we observed the bulk conduction and grain boundary diffusion.

A new ultrasonic interferometer for velocity measurement in liquids using optical diffraction

A new ultrasonic interferometer for velocity measurement using optical diffraction and an optical heterodyne system is described. The velocity of pure water at 20 degrees C has been measured in the frequency range 0.5-5 MHz, and the velocity obtained increases with decreasing ultrasonic frequency. In order to clarify the behaviour, a new theory for the ultrasonic interferometer is given and the usefulness of the instrument is shown by using it to measure the velocity dispersion in benzene.

Lattice Distortion and Lithium Ionic Conduction Path in a Superionic Conductor with Perovskite Structure

Three-dimensional structure for La 2/3- x Li 3 x TiO 3 was deduced by the reverse Monte Carlo (RMC) modeling technique on the basis of X-ray and neutron diffractions to reveal the lattice distortion relating to the disorder in the distributions of La ions and the conduction path of Li ions. Our previous results focused on Li ion distribution on the average lattice structure obtained from Rietveld analysis and revealed that the Li ions were mainly situated on the La-rich layer which is completely different from the earlier works. In the present study where physical constraints on La, Ti, and O atoms forming the lattice structure have been relatively released during RMC modeling, we analyzed the distortion of TiO 6 octahedra to check the difference between our study and the earlier studies. In addition of the consistency of our structural model with the earlier studies in terms of the Ti and O positions, and the tilting angle of about 10° for TiO 6 octahedra, it has been analyzed their fluctuations from the...

Mixed ion effect in Li/Na–NaZr2(PO4)3

Abstract The mixed ion effect (MIE) in Li/Na–NaZr 2 (PO 4 ) 3 with a three-dimensional diffusion path was observed. The conductivity minimum at an ionic ratio 0.8 was lower by about three orders of magnitude than for either end member. Hexagonal parameters a , c and 7 Li MAS/NMR spectral intensity against the ionic ratio showed a linear change. The spectral width of 31 P MAS NMR at chemical shift 5.9 ppm against the ionic ratio showed a minimum at the same ionic ratio with the conductivity data. The behavior suggests that the conductivity minimum results from the inhomogeneous distribution of two unlike ions and a blocking of diffusion path.