Raman scattering and interaction and interference of optical vibrations in a γ-Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> superionic crystal

Polarized Raman spectra of γ-Li₃PO₄ single crystal are investigated at temperatures approximately up to 700 K. It is shown that vibrations of PO₄ tetrahedrons and cations of the lithium sublattice can be separated in the spectra. It is found that an increase in temperature leads to interference of one-phonon optical modes of symmetry B_2g and A _g , which is accompanied by antiresonance in a frequency range near 190 cm^?1. Numerical analysis of the spectrum in the region of interaction of optical modes reveals a strong temperature dependence of the interaction constant, which is determined by anharmonic coupling of optical and acoustic modes.     

Ionic conductivity of isostructural crystals of the superionic conductors Li3Fe2(PO4)4 and Li3Sc2(PO4)3

The results of measurements of the ionic conductivity σ in Li₃M₂(PO₄)₃ (M=Fe, Sc) single crystals along various crystallographic directions are analyzed. Possible causes of the different behavior of σ in the isostructural crystals are discussed: a jump of the conductivity in the transition to the superionic phase in Li₃Sc₂(PO₄)₃ and its absence in Li₃Fe₂(PO₄)₃; the existence of a conductivity maximum in different crystallographic directions (along the c axis in Li₃Sc₂(PO₄)₃ and along the a axis in Li₃Fe₂(PO₄)₃). Fiz. Tverd. Tela (St. Petersburg) 39, 83–86 (January 1997)     

Prediction of transport properties of new functional materials based on lanthanum-strontium cuprates: Molecular mechanics calculations

The method of molecular dynamics is used for prediction of properties of new functional materials based on lanthanum-strontium cuprates La_{2 ? x} Sr _x CuO_{4 ? δ} as new materials of the solid state ionics. The most interesting phases are synthesized to test the obtained calculation data and their electrophysical and thermomechanical characteristics are studied. It is shown that the high values of the oxygen diffusion coefficients are obtained in the La_{2 ? x} Sr _x CuO_{4 ? δ} solid solutions with a high replacement degree of Sr → La (up to x = 1). The calculated values of lattice cell parameters, thermal expansion coefficients and oxygen diffusion coefficients agree with the experimental data. The observed anisotropy of anionic transport for all the studied compositions corresponds to the regularities of crystal structure of complex oxides. Using the molecular dynamics method allows tracing the contribution of separate types of oxygen ions (equatorial and apical) into ionic transport at the microscopic level and also confirming directly that oxygen diffusion occurs according to the usual jump mechanism, mainly in (CuO₂) layers.     

Mechanism of structural phase transitions in the Li4GeO4-ZnGeO4 system: Computer modeling and identification of invariant nanocluster structures in Li4GeO4, LISICON Li6Zn(GeO4)2, and Li4Zn2(GeO4)2 (γ phase)

The cluster modeling of structural phase transitions Li₄GeO₄ ?? LISICON Li₆Zn(GeO₄)₂ ?? ??-Li₄Zn₂(GeO₄)₂ was carried out using computer-assisted methods (the TOPOS program package). The precursor nanoclusters of crystal structures were recognized in an automated data processing mode using an algorithm developed for selecting combinations from nonintersecting suprapolyhedral clusters. 3D macro-structure modeling employed the principle of maximal space filling and, accordingly, took into account the requirement for the maximal complementary connectivity of precursor nanoclusters in crystal structure self-assembly followed by consecutive primary chain-microlayer-microframework assembly. A crystallochemically correct structure model was advanced for superionic LISICON Li₆Zn(GeO₄)₂ as a 2D analogue of Li₄GeO₄ containing only two types of voids in a layer, which are most likely to be sites for Li atoms to reside. A migration map was constructed to characterize the 2D set of conductivity channels in superionic LISICON.     

Synthesis and crystal structure of Li3.17(P0.69Ge0.24Mo0.07)O4

The crystal structure of Li_3.17(P_0.69Ge_0.24Mo_0.07)O₄, which was synthesized by the flux method under the action of an electric field with a potential difference of 0.8 V, was studied by X-ray diffraction on a Nonius Kappa CCD diffractometer (MoK _α radiation, λ = 0.71073 Å, R = 0.0137). The crystal structure is based on a tetrahedral framework typical of γ-Li₃PO₄. The framework of the new compound is formed by (P,Ge,Mo)O₄ and LiO₄ tetrahedra. The positions of additional Li atoms in the structure of Li_3.17(P_0.69Ge_0.24Mo_0.07)O₄ are found to be different from those in the structure of Li_3.31(P_0.69Ge_0.31)O₄, which is synthesized in the absence of an electric field and also belongs to the γ-Li₃PO₄ structure type.     

Analysis of Li<Superscript>+</Superscript> cation migration paths in oxygen-containing compounds

Novel method for the studying of voids and channels in crystal structures is developed on the basis of the TOPOS structure-topology software. The method is using the Voronoi-Dirichlet crystal space partition. All ternary and quaternary lithium-containing inorganic compounds whose structure has been studied (822 compounds of the Li _a X _b O _z composition and 1349 compounds of the Li _a X1 _b X2 _c O _z composition, where X, X1, and X2 is any chemical element) are analyzed for the first time. The dimensionality of systems of the channels capable of transporting lithium ions is revealed. For all compounds, the migration patterns are constructed, which characterize systems of the conductance channels with the dimensionality 1, 2, and 3; the theoretically calculated coordinates of lithium atom positions in the voids’ centers agree well (accurate within 0.06 nm) with the known structure data. It is found, that 275 compounds have infinite channel system. Of this sampling, 249 compounds (125 structural types) have been described as solid electrolytes; the rest (26 compounds) can be thought of as potential ionic conductors with one-dimensional (6 types), two-dimensional (2 types), or three-dimensional (18 types) conductance.     

Growth,Structure, and Electrophysical Properties of Single Crystals of A2TiGeO5 (A = Li and Na)

Crystals of Li₂TiGeO₅ were obtained by solution-melt crystallization, and those of Na₂TiGeO₅ were grown from a melt by pulling. The crystals are isostructural with the natisite mineral Na₂TiSiO₅. The crystal structure of Li₂{TiOGeO₄} was refined by X-ray diffraction analysis (a four-circle diffractometer, 2/ scan mode, MoK radiation, _max = 50°). The unit cell parameters are a = 6.614(4) Å and c = 4.435(4) Å; space group P4/nmm, Z = 2, _calcd = 3.67 g/cm³, R = 0.031, s = 1.128, wR(F ²) = 0.071 (548 reflections with I 2I). The ionic conduction in both crystals was found to be anisotropic in the temperature range 250–600°C;. At 400°C;, the conductivity values are 10^–4 to 10^–5 S/cm along the a axis and 10^–6 to 10^–8 (for Na₂TiGeO₅) and 10^–7 to 10^–9 S/cm (for Li₂TiGeO₅) along the c axis.     

The influence of plasma chemical treatments on the activity of the Li3Fe2(PO4)3 catalyst in butanol-2 transformations

The influence of plasma chemical treatments in oxygen, hydrogen, and argon on the catalytic activity of Li₃Fe₂(PO₄)₃ was studied for the example of butanol-2 transformations. Plasma chemical treatment was found to be an effective method for increasing catalyst activity and changing its selectivity. The character of activation depends on the selection of the plasma-forming gas. The highest activity in the dehydration of butanol-2 was observed after treating the catalyst in hydrogen under glow discharge conditions.