Interrelation of structural features and vibrational dynamics of atoms in the crystal lattice of lithium orthogermanate in the superionic state

The crystal structure and vibrational dynamics of lithium atoms in Li_3.75Ge_0.75V_0.25O₄ and Li_3.70Ge_0.85W_0.15O₄ solid electrolytes in the superionic state are investigated using neutron diffraction and nuclear magnetic resonance (NMR) spectroscopy. It is found that, in the crystal lattice, lithium ions occupy four nonequivalent positions in the tetrahedral and octahedral oxygen ion environment with vacancies in the octahedra. These findings are in good agreement with the NMR data on the dynamic inhomogeneity of lithium cations in the lattice. It is shown that the origin of the superionic state in the studied compounds is associated primarily with the geometric factor, i.e., with an increase in the size of cavities in the oxygen polyhedra surrounding lithium cations.     

Electron transition in intercalated disulfide CuCrS<Subscript>2</Subscript>

Electrical, resonant, and magnetic properties of intercalated copper chromium disulfide CuCrS₂ are studied. It is established that CuCrS₂ is an antiferromagnetic semiconductor with Néel temperature T_N=40.7 K and an effective magnetic moment of 4.3µ_B. Anomalies in the electrical, magnetic, and resonant properties of CuCrS₂ are found at T_c=110 K, which suggest an electron transition accompanied by alteration of the valences of the 3d-metal ions.     

Investigation of superionic phase transition in the CuCr1−x VxS2 system by x-ray diffraction and magnetic methods

The unit cell parameters and the distribution of copper atoms over different crystallographic sites in the CuCr_1?x V_xS₂ superionic conductors have been determined by x-ray diffraction. It is demonstrated that a jumpwise change in the copper occupancy of different crystallographic sites for the compositions with x=0, 0.05, 0.1, and 0.15 is associated with the transition to the superionic phase. The two-dimensional character of the ion transfer in the studied compounds is confirmed. No considerable anomalies in the temperature dependences of the paramagnetic susceptibility are revealed at temperatures of the superionic transition.     

Structural studies and ionic conductivity of CuCr1−xVxS2 (0 ≤ × ≤ 0.3)

CuCr_1−xV_xS₂ (0 ≤ × ≤ 0.3) is isostructural with CuCrS₂. The substitution of Cr by V results in the partial transition of Cu atoms into the disordered state and in an increasing Cu⁺ ion conductivity.     

Anomalous Raman phenomenon of CuCrS2

Structural dynamics of the layered CuCrS₂ is investigated for the first time by using the Raman scattering method in 78–295 K temperature range on the samples synthesized by different methods. The Raman and IR spectra of CuCrS₂ were simulated within the valence force field model with the LADY program. The results presented indicate that the lattice dynamics of CuCrS₂ depends strongly on the real microstructure and technology of the sample preparation. The anomalous splitting of the A₁ phonon mode might be due to presence of the α‐ and β‐domains. Copyright © 2010 John Wiley & Sons, Ltd.     

Superstructure Ga4InAs5

An epitaxial layer of the Ga_0.82In_0.18As solid solution is investigated. The coordination of arsenic atoms in the structure of this compound is determined by x-ray diffractometry. The ratio of arsenic atoms in the coordination 4Ga, 3Ga + In, and 2Ga + 2In corresponds to the superstructure in which an In atomic chain along the [110] direction alternates with four Ga chains. An ideal composition for this superstructure is Ga₄InAs₅. New specific features of the domain structure formed as a result of temperature-induced changes in the configuration of tetrahedral bonds are revealed.     

Structural study of CuCr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>2</Subscript> substitutional solid solutions

The local structure and charged state of metal atoms in the CuCrS₂ matrix and CuCr_{1 − x} V _x S₂ solid solutions of substitution of vanadium for chromium (0 < x < 0.25) are studied by x-ray absorption spectroscopy (XAFS) using synchrotron radiation. According to XANES spectra (near-edge fine structures), introducing vanadium does not change the charged state of matrix elements and they exist as Cu(1+), Cr(3+), V(3+), and S(2−) in the solid solution. According to EXAFS spectra (extended fine structures), introducing vanadium slightly distorts the local structures of both Cr and Cu atoms (to a greater extent for copper than for chromium). The XAFS analysis data show that vanadium only partially filled vacant positions (specified by the composition of the initial mixture) in the chromium sublattice, the majority of them being located in irregular positions of slightly distorted octahedrons consisting of sulphur atoms. It is shown that the substitution effect leads to deformation (compression) of the lattices of CuCr_{1 − x} V _x S₂ samples without changing their crystallochemical structures and symmetries, but changes their magnetic structures.     

Self-organization of particles in the superionic phase of lanthanum trifluoride

When a laser beam (λ = 396.3 nm) propagates through a nonuniformly heated superionic LaF₃ crystal in the direction of lattice constant c, alternating bright and dark fringes arise on the screen. The fringes run from the warmer face to the colder one. The number and width of the fringes are found to depend on the temperature gradient in the crystal: the smaller (greater) the temperature difference between the faces, the smaller (greater) the number of moving fringes. It is the author’s opinion that this effect is due to the wave transfer of applied heat and reflects the self-organization and collective displacements of the ions of the “quasi-liquid” sublattice in a nonuniform temperature field. A qualitative model of heat wave transfer in the LaF₃ superionic phase is suggested.     

Dielectric properties,ionic conductivity and phase transitions in La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics

The dspersion dielectric permeability and ion conductivity of La₂Mo₂O₉ ceramics was studied. It was established that the observed low-frequency dielectric dispersion is due to relaxation effects related to high ion conductivity. It is shown that the phase transition in La₂Mo₂O₉ has characteristic features of a superionic phase transition.     

Investigation of ionic conduction in the mixed AgI-PbI2 system

Study of ionic conductivity in AgI-PbI₂ system has a function of composition and temperature shows that PbI₂ has a definite role in the process of superionic phase transition. It has been found that at 80 mole % of AgI, superionic phase transition temperature passes through a minimum value of as low as 105°C. The maximum conductivity (at room temperature) is also obtained in this region. The results are discussed qualitatively in terms of a lattice loosening model.     

RDF studies of the superionic conductor RbAg4I5 using EXAFS

Measurements of the extended X-ray absorption fine structure (EXAFS) on the Ag K-shell absorption in RbAg₄I₅ show that in all three crystalline phases the equilibrium position of the Ag ions is near the center of tetrahedra formed by the iodine atoms. In addition, Ag-Ag correlations, which persist into the superionic α-phase, are observed.     

熔融Rb2ZnCl4的分子动力学模拟研究

采用在RbCl模拟和ZnCl₂模拟中选用的两体有效势，进行了晶态和熔融态Rb₂ZnCl₄的分子动力学模拟.模拟给出了Rb₂ZnCl₄ 6种径向分布函数，Zn-Cl和Rb-Cl间径向分布函数与新近的广延X射线吸收精细结构实验结果很好相符.在模拟产生的瞬态构型基础上进行了键序参数分析，研究了晶态和熔融态中的局部结构.模拟结果表明，Zn原子与其近邻Cl原子构成相当稳定的正四面体结构，并且熔融Rb_关键词：     

129I-Mössbauer spectroscopic study of iodide-containing chalcogenide glasses

¹²⁹I-Mössbauer spectroscopy was used to study the short-range order in I-containing chalcogenide glasses. It was found that AsXI glasses, where X=S or Se, are molecular solids composed from molecular units of arsenic iodide and arsenic chalcogenide. The local environment of iodide ions in ternary superionic conducting glasses AgI?Ag₂S?As₂S₃ is similar to that in the crystalline superionic conductor Ag₃SI and differs distinctly from iodide local order in binary vitreous alloys AgI?As₂S₃ and crystalline AgI.¹²⁹I-Mössbauer spectra of all glasses were fitted satisfactory, when a distribution of the electric-quadrupole coupling constant is taken into account.     

Point defect parameters for β-PbF2 from a computer analysis of measurements of ionic conductivity

The conductivity of four crystals of β-PbF₂ has been measured. The results for three of these crystals, one doped with La³⁺ and two doped with Na ⁺ impurity, have been analysed with a non-linear least squares programme to yield the thermodynamic parameters of defect formation and migration below the superionic transition. These parameters are compared with previous values and are used to provide estimates of the defect concentrations in the superionic phase. This work suggests that the superionic phase is not massively disordered and that β-PbF₂ is not significantly different from other fluorites.     

Density functional study of low-lying isomers of SiO<Subscript>4</Subscript>, GeO<Subscript>4</Subscript> and CO<Subscript>4</Subscript>, and their relation to tetrahedral solid phases

In silica (SiO₂) and in most silicates, atomic associations exist with composition SiO₄ and a structure with four O atoms in tetrahedral coordination around the Si atom. A similar feature is observed in germania (GeO₂) and some solids containing Ge instead of Si, although the number of phases containing GeO₄ tetrahedra is smaller. In contrast, and in spite of the fact that C is in the same column of the periodic table as Si and Ge, CO₂ is a molecular solid, and crystalline and amorphous phases of CO₂ showing CO₄ tetrahedra are only obtained under extremely high pressures. We have investigated the relation between free SiO₄, GeO₄ and CO₄ clusters and the tetrahedral associations found in the solids mentioned above. The lowest energy structure of those three free clusters is planar, but they have near-tetrahedral and distorted-tetrahedral isomers. The promotion energy from the planar structure to the distorted tetrahedral is low in SiO₄, large in CO₄, and intermediate in GeO₄. This correlates with the facility to form tetrahedral associations in the solids.     

New approach to treating the energetics of activation processes in the lattice of superionic conductors with intrinsic structural disorder

Using LaF₃-type superionic trifluorides as an example, it is shown that the intrinsic thermal structural disorder not affecting the symmetry of the lattice is embodied in light inelastic scattering spectra. Tools for analyzing the Arrhenius-like temperature dependence of the activation energy of disordering in the superionic conductor lattice are discussed. It is found that activation energy ΔEa found from the temperature dependence of the Raman line width is many times lower than energy Ea responsible for LaF₃ lattice disordering.     

The ionic Seebeck effect and heat of cation transfer in Cu2−δSe superionic conductors

The ionic Seebeck coefficients of Cu_2?δSe superionic conductors are measured in the temperature range 340–380°C. The data obtained are used to determine the heat of transfer Q _i of copper ions as a function of the degree of nonstoichiometry and the temperature. The heat of transfer of copper cations increases from 0.19 to 0.22 eV as the degree of nonstoichiometry δ increases from 0.015 to 0.050. It is noted that the heat of transfer Q _i tends to increase with an increase in the temperature. Assumptions regarding the specific features of the cation diffusion in the Cu_2?δSe superionic conductors are made from the observed closeness of the heat of transfer and the activation energy for ionic conduction.     

Site dependent hardening of the lanthanum metal lattice by hydrogen absorption

The compressibility of lanthanum (La) metal and its hydrides were measured at room temperature by high pressure synchrotron X-ray diffraction. La metal pressurized in a hydrogen medium forms a hydride with an fcc metal lattice, which likely contains hydrogen at a concentration close to 3.0 and persists over the measured pressure span up to 21 GPa. Equations of state have been determined by helium compression experiments for LaH₂ with tetrahedral interstitial sites fully occupied with hydrogen atoms and for LaH_2.46 with octahedral interstitial sites partially occupied with hydrogen atoms and tetrahedral sites fully occupied. Both hydrides possess fcc metal lattices. The bulk modulus values B₀ are 66.7 ± 1.2 GPa for LaH₂ and 68.4±1.0 GPa for LaH_2.46. These values are three times larger than that of La metal and are very close to each other despite the difference in hydrogen occupation states. The hardening of the metal lattice by hydrogenation is attributed predominantly to hydrogen-metal interactions at the tetrahedral sites and is most pronounced for La, which has the largest ionic radius among rare-earth metals.     

Magnetic resonance in a Cu-Cr-S structure

A layered Cu-Cr-S structure composed of single-crystal CuCrS₂ layers and thin CuCr₂S₄ plates embedded in them has been investigated by the magnetic resonance and scanning electron microscopy methods. The Curie temperature and saturation magnetization of the spinel phase of the investigated samples have been determined. The thickness of the CuCr₂S₄ layers has been estimated. The dependence of the growncrystal topology on synthesis conditions has been established. An interpretation of the anomalous behavior of the magnetostatic oscillation intensity is offered.     

Ion dynamics and sublattice melting in the superionic conductor PbF2

The F¹⁹ relaxation rates in PbF₂ exhibit anamolous changes as the temperature is increased into the superionic phase. These changes confirm the concept of a continuous melting of the fluorine sublattice and show that the fluorine motion in the superionic phase is highly correlated.