Ionic Sublattice Research Articles

Salt‐Inclusion Synthesis of Two New Polar Solids, Ba6Mn4Si12O34Cl3 and Ba6Fe5Si11O34Cl3.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Thermodynamic Modeling of the Binary Barium–Oxygen System

The phase equilibria and thermodynamic properties of the binary Ba–O system were analyzed. The Gibbs energy functions of individual phases were modeled, and the model parameters were obtained by means of the CALculation of PHAse Diagram (CALPHAD) technique, based on available experimental data in the literature. The liquid phase was described with a two‐sublattice ionic model. For the non‐stoichiometric BaO and BaO2 phases, a two‐sublattice ionic model was applied, and two sets of Gibbs energy functions were obtained by treating them either as separate phases or as a common solution phase with a miscibility gap. The ionic sublattice models used in the present work provide an approach to better describe the physical behavior of the Ba–O binary system such as defect chemistry and doping effects, which will be studied in multicomponent systems.

Salt-Inclusion Synthesis of Two New Polar Solids, Ba6Mn4Si12O34Cl3 and Ba6Fe5Si11O34Cl3

A new family of salt-containing, mixed-metal silicates (CU-14), Ba6Mn4Si12O34Cl3 (1) and Ba6Fe5Si11O34Cl3 (2), was synthesized via the BaCl2 salt-inclusion reaction. These compounds crystallize in the noncentrosymmetric (NCS) space group Pmc2(1) (No. 26), adopting 1 of the 10 NCS polar, nonchiral crystal classes, mm2 (C2v). The cell dimensions are a = 6.821(1) A, b = 9.620(2) A, c = 13.172(3) A, and V = 864.4(3) A3 for 1 and a = 6.878(1) A, b = 9.664(2) A, c = 13.098(3) A, and V = 870.6(3) A3 for 2. The structures form a composite framework made of the (M(4+x)Si(12-x)O34)9- (M = Mn, x = 0; M = Fe, x = 1) covalent oxide and (Ba6Cl3)9+ ionic chloride sublattices. The covalent framework exhibits a pseudo-one-dimensional channel where the extended barium chloride lattice (Ba3Cl1.5)(infinity) resides, and it consists of fused eight-membered meta-silicate rings propagating along [100] via sharing two opposite [Si2O7]6- units to form an acentric lattice. Single-crystal structure studies also reveal the ClBa4 unit adopting an interesting seesaw configuration, in which the lone pair electrons of chlorine preferentially face the oxide anions of the transition metal silicate channel, thus forming the observed polar frameworks. Similar to the synthesis of organic-inorganic hybrid materials, the salt-inclusion method facilitates a promising approach for the directed synthesis of special framework solids, including NCS compounds, via composite lattices.

Phase diagram of the ZrO 2–Gd 2O 3–Al 2O 3 system

Isothermal sections of the phase diagram for the ZrO 2–GdO 3/2–AlO 3/2 system have been constructed based on experimental phase equilibrium data at 1250 and 1650 °C. They are in a good agreement with calculations which have also been performed in the present study. The liquidus and solidus surfaces have been experimentally determined. The temperature of the eutectic reaction liquid = Al 2O 3 + fluorite + GdAlO 3 was measured using differential thermal analysis (DTA) to be 1662 °C. The liquidus surface calculated in this work using a non-zero ternary interaction parameter in the liquid phase agrees with the experimental data. A thermodynamic description of the ZrO 2–GdO 3/2–AlO 3/2 system based on an ionic sublattice model for the solid and liquid phases consistent with the experimental data has been derived.

Atomic resolution imaging of the (001) surface of UHV cleaved MgO by dynamic scanning force microscopy.

The (001) surface of UHV cleaved single MgO crystals was imaged with dynamic mode scanning force microscopy. Large-scale images show various defects, like steps of mostly one atomic height, rectangular holes of nanometer size, and some complex adstructures. First time images with atomic resolution show one square ionic sublattice in its bulklike dimension with a corrugation of up to 40 pm along the <001> direction. Most images exhibit atomic point defects which appear as depressions including a few ionic lattice sites proving that point defects are stable on flat terraces.

Structure-forming components in crystals of ternary and quaternary 3d-metal complex fluorides.

Crystallochemical analysis and classification were performed for 139 ternary and quaternary complex fluorides with the general formula M1(n)M2(m)M3F(6), belonging to 33 structure types. Using coordination sequences and the uniformity criterion the structure-forming ionic sublattices or their combinations were found, which are responsible for the formation of stable periodic frameworks. Analysis of structure-forming motifs allows the interpretation of the crystal structures of complex fluorides as close packings of F ions with M1, M2 and M3 cations, partially occupying tetrahedral and octahedral voids, or as the packings of [M3F(6)] complex ions with M1 and M2 countercations in the voids. Cationic sublattices are noted to play an essential role, while forming crystal structures of complex fluorides. Relationships between the composition of structure-forming sublattices, the composition of compounds, and the size and charge of ions belonging to the sublattices were analysed under normal conditions, with thermal and high-pressure polymorphic transitions. Rules were formulated to predict the crystal structures of complex fluorides with a given chemical composition.

Heterostructured high-Tcsuperconducting nanohybrid:(Me3S)2HgI4−Bi2Sr2CaCu2Oy

We have developed a type of nanohybrid high-$T$ superconductor with periodic stacking of the organic-salt layer and the superconducting cuprate one. Such a hybrid is realized by intercalative complexation, which means that complex formation proceeds in the interlayer space of two-dimensional solid lattice by reacting trimethylsulfonium iodide with the ${\mathrm{HgI}}_{2}$-intercalated bismuth cuprate. The present organic-salt intercalate provides a clue to understand the high-${T}_{c}$ superconductivity in the layered cuprate and, at the same time, the synthetic strategy gives an interesting route to a different class of high-${T}_{c}$ superconducting nanohybrid. The powder x-ray-diffraction pattern shows that the organic-inorganic hybrid material features a stage-I intercalation compound with a basal increment of 12.6 \AA{} compared to the pristine. The micro-Raman analysis reveals that the intercalated ionic sublattice consists of tetrahedral complex anion $({\mathrm{HgI}}_{4}^{2\ensuremath{-}})$ and organic cation ${(Me}_{3}{S}^{+}),$ which is also cross confirmed by the extended x-ray-absorption fine-structure fitting results. In spite of large layer separation, the onset ${T}_{c}$ of the nanohybrid is comparable to that of the pristine compound, unusual phenomena when compared with ${T}_{c}$ depressions in the iodine-, AgI-, and $\mathrm{Hg}{X}_{2}$ $(X=\mathrm{Br}$ and I)-intercalated Bi-based cuprates.

Topological analysis of ionic packings in crystal structures of inorganic sulfides: the method of coordination sequences

Abstract Using the concept of coordination sequences and the uniformity criterion the method of topological analysis of atomic packings and of their classification at any degree of metric distortions is implemented in the computer program IsoTest. The criterion is based on the search for packings topologically similar, but not equal to close packings. The topological analysis of ionic sublattices was employed for the crystal structures of 781 inorganic sulfides. It was shown that no less than in the third of cases the sulfides are constructed on the basis of a distorted close packing, and such packings are constructed with sufficiently large cations, as a rule. The examples of forming close packings by complex thioanions contained in a number of thiosalts were drawn.

Search for isotypism in crystal structures by means of the graph theory

A method for the classification of crystal structures of chemical compounds is proposed, which is based on the representation of the system of interatomic bonds in a crystal as a finite 'reduced' graph. The program IsoTest is described, allowing one to find automatically the topological similarity (isotypism) for large groups of stoichiometrically and structurally different compounds. The analysis of crystal structures of simple and double sulfates and binary inorganic compounds was carried out and numerous examples of topological isotypism of the representatives of these groups of substances were found. It is shown that in many cases the ionic sublattices, constructed according to one of the close packings, can be selected in the sulfate crystal structures.

Dislocation mechanism and kinetics of shock-induced phase transformation in KCl

A high-speed dislocation mechanism of the phase transition in potassium chloride under shock loading is suggested. At shock pressures exceeding the equilibrium pressure of the phase transformation, the shock-induced shear stress provides the generation, motion and multiplication of partial dislocations of the initial lattice B1 (rocksalt-type; two face-centered cubic sublattices of ions of opposite sign). This results in the development of the intermediate B ∗ structure (two ionic sublattices of like sign: unchanged, face-centered cubic, and transformed, base-centered orthorhombic) with further transformation into the final cesium chloride structure B2 (two simple cubic sublattices of ions of opposite sign). Since the unrelaxed shear stress favors an easy dislocation climb, the transformation rate is very high, varying from 1 to 3 nsec −1, for different orientations of the shocked crystal. This rate is typical for the first stage of transformation, B1 → B ∗ . A comparatively low (5–25 μsec −1) transformation rate at the second stage, B ∗ → B2 , is due to the decrease of ability of dislocations to cross the parallel glide planes and to the closure of new phase regions impeding the forward motion of dislocations.

THE NONLINEAR EXCITATIONS AND THEORY OF PROTON TRANSFER IN HYDROGEN BONDED MOLECULAR SYSTEMS

Based on the analysis of properties of protonic excitation and displacements in the hydrogen bonded molecular systems we proposed here a new model Hamiltonian and theory for studying the properties of nonlinear collective excitation and proton transfer resulting from the localized fluctuation of protons and the deformation of structure of heavy ionic sublattice owing to the protonic displacements.We give the equations of motion and corresponding solutions of solitons,discuss the features and meanings of these solutions and the advantages of our model,and explain completely motion of two kinds of defects and proton transfer in the hydrogen bonded molecular systems.

Photoinduced phenomena in RbAg4I5superionic crystals

Abstract We have observed a new phenomena of photoinduced transformation of Raman scattering and photoluminescence spectra in RbAg 4 I 5 superionic crystal. A reversible change of the fine structure in Raman spectra at low temperature and reversible change of the concentration of luninescence centers due to irradiation of sample have been studied. Both of these processes are due to the change of local concentration of mobile silver ions in irradiated region of RbAg 4 I 5. The mechanism of interaction between nonequilibrium electrons and silver disordered ionic sublattice has been proposed. The excess concentration of electrons gives rise to diffusion flow of electrons and ions from irradiated region.

Photoinduced phenomena in RbAg 4I 5 superionic crystals

We have observed a new phenomena of photoinduced transformation of Raman scattering and photoluminescence spectra in RbAg 4I 5 superionic crystal. A reversible change of the fine structure in Raman spectra at low temperature and reversible change of the concentration of luminescence centers due to irradiation of sample have been studied. Both of these processes are due to the change of local concentration of mobile silver ions in irradiated region of RbAg 4I 5. The mechanism of interaction between nonequilibrium electrons and silver disordered ionic sublattice has been proposed. The excess concentration of electrons gives rise to diffusion flow of electrons and ions from irradiated region. A creation of hole trapped centers in irradiated region of γ-RbAg 4I 5 puts additional constraints on Ag site occupancy. Therefore, for irradiated γ-RbAg 4I 5, a “random tetrahedral” model has been used to describe a reversible change of the fine structure in Raman spectra at low temperature.

Ionic Transport in Amorphous Solid Electrolytes

Until recently, electrochemistry has been mainly involved with liquid electrolytes, traditionally molten and dissolved electrolytes. Because their domain of electroactivity is often too narrow and their selectivity is poor with respect to the nature of the charge carrier, these electrolytes have proved unsuitable for energy storage in high density energy storage batteries. Consequently, in recent years a great deal of research has been devoted to another type of electrolyte: crystallized solid state electrolytes. Roughly, there are two types of solid electrolytes. First there are electrolytes conducting through point defects. These include alkali and alkaline earth halides and some oxides. They have a compact crystalline structure, and ion displacement is only possible because of point defects such as vacancies or interstitial ions. These conductors present an intrinsic conduction, associated with the con­ centration of defects of thermal origin, Frenkel or Schottky disorder, and an extrinsic conduction associated with the concentration of point defects in the ionic or cationic sublattice created by impurities. Intrinsic and extrinsic conduction are both characterized by an activation energy. The intrinsic conduction activation energy is always high since it is the sum of two terms-one representing the energy needed to form a point defect, and the second the migration energy of this defect. In the extrinsic domain, at lower temperature, the activation energy is lower since it reflects only the migration energy. The value I eV often constitutes a boundary between the two types of conduction. Secondly, there are solid state electrolytes that conduct through dis­ order of the sub lattice of one of the ions. They include electrolytes such

Abrupt change of ionic conductivity induced by an electric field

A theory of abrupt disordering of one of ionic crystal sublattices in an external electric field is developed. It is shown that it is possible to transfer a crystal into a high-conductivity state without heating by means of a field-induced phase transition.