Oxygen ion concentration in solvents for the growth of garnets

A concentration cell for the determination of the oxygen ion concentration by means of e. m. f. measurements is described which is suitable for oxidic melts with low viscosity and high attack on ceramic materials. Applying this concentration cell binary mixtures of oxides and fluorides used as solvents for the garnet preparation were investigated. The oxygen ion concentration is given in dependence on the composition of the mixtures. By comparison with simple models conclusions on the structure of the melt are made.     

Analysis of the electronic dipole polarizability of ions in cubic oxides,fluorides, and sulfides of alkaline earth elements

A new approach to calculating the electronic dipole polarizability of ions in crystals which is based on an analysis of the relationship between the electronic dipole polarizability of ion and its effective charge has been proposed. It is shown that applying this method to simple cubic oxides, fluorides, and sulfides of alkaline earth elements yields makes the calculation results consistent with the well-known data on the structure and type of bonds in these compounds.     

Nonstoichiometry in Inorganic Fluorides. IV: The Initial Stage of Anionic Nonstoichiometry in RF3 (R = Y,La, Ln)

Crystallography Reports - The anionic nonstoichiometry in inorganic fluorides is at result of substitution of F1– for O2– in the anionic sublattice. All families of fluorides exhibit...     

Geometrical laws in inorganic chemistry

On the basis of an original interpretation of the crystal state, it is shown that most of the structural types are determined by a small set of planar nets densely filled with the heaviest atoms of the structure. These nets are combined into atomic sublattices (matrices of the structure types) by the operations of (pseudo) symmetry, thus reducing the number of the degrees of freedom in the structure, which, in turn, provides structure stability. It is shown on examples of heavy-cation oxides, fluorides, and sulfides that the number of the types of such matrices (F-, I-, etc.) is limited. Each type is characterized by a certain structure-determining complex of mutually intersecting crystallographic planes parallel to the most densely filled atomic nets. Most of the atomic nets considered in crystal chemistry are, in fact, various sections of the sublattices-matrices formed by a limited number of densely filled atomic nets.     

Chemical aspects of crystal growth of multicomponent fluoride materials from the melt

Chemical aspects of crystal growth of fluoride materials from the melt are considered. The high aptitude of fluorides to pyrohydrolysis (reaction with water vapour at high temperatures) to a large extent accounts for the specific chemical features of the conditions of preparing their single crystals. The processes of pyrohydrolysis in the well-known industrial techniques used to prepare crystals of alkaline-earth fluorides (MF₂) are reported. The review provides data on the stage mechanism of fluorite pyrohydrolysis, fluorite being the main fluoride optical material. The forms of external manifestation of pyrohydrolysis in crystals are considered. Classification of the techniques of fluoride purification from the oxygen impurity is given in reference to the extent of purification. The fluorinating atmospheres used in fluoride crystal growth are described. The review reports data on the interaction between gaseous fluorinating agents and fluoride melts with graphite, which is the main construction material used in crystal growth devices.     

Nonstoichiometry in inorganic fluorides: I. Nonstoichiometry in MF m -RF n (m < n ≤ 4) systems

The manifestation of gross nonstoichiometry in MF _m -RF _n systems (m < n ?? 4) has been studied. Fluorides of 34 elements, in the systems of which phases of practical interest are formed, are chosen. To search for new phases of complex composition, a program for studying the phase diagrams of the condensed state (??200 systems) has been carried out at the Institute of Crystallography, Russian Academy of Sciences. The main products of high-temperature interactions of the fluorides of elements with different valences (m ?? n) are grossly nonstoichiometric phases of two structural types: fluorite (CaF₂) and tysonite (LaF₃). Systems of fluorides of 27 elements (M ¹⁺ = Na, K; M ²⁺ = Ca, Sr, Ba, Cd, Pb; R ³⁺ = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; R ⁴⁺ = Zr, Hf, Th, U) are selected; nonstoichiometric M _{1 ? x} R _x F _{m(1 ? x) + nx} phases, which are of greatest practical interest, are formed in these systems. The gross nonstoichiometry in inorganic fluorides is most pronounced in 80 MF₂ ? RF₃ systems (M = Ca, Sr, Ba, Cd, Pb; R are rare earth elements). The problems related to the growth of single crystals of nonstoichiometric phases and basic fields of their application as new fluoride multicomponent materials, the properties of which are controlled by the defect structure, are considered.     

Nonstoichiometry in Inorganic Fluorides. III: Anionic Nonstoichiometry in MF2 (M = Ca,Sr, Ba)

Crystallography Reports - Anionic nonstoichiometry in fluorides (replacement of F1– with O2–) deteriorates the quality of optical materials. Two reviews have been devoted to the initial...     

Peculiarities of the structure of precrystallization state of amorphous and liquid metals

The phase and structural transformations in the molecular dynamics models of iron and Fe-B alloys are investigated using smooth and oscillating potentials for interaction of Fe-Fe pairs. To analyze the changes in the structure of materials during heat treatment, local time-averaged pair distribution functions and time-dependent van Hove functions are calculated, along with the standard functions. When studying the vibrational spectra, specific atoms are chosen from nanocrystals of different sizes or from the amorphous phase. The differences found in the periods of structural changes before the formation of bcc and fcc crystal phases, in the vibrational spectra of nanocrystals of different sizes, and in the distributions of waves over their wavelengths are described. A simple parameter is proposed to characterize the degree of structural quality of nanocrystals.     

On the nature of unique boron sites in borate glasses

The ¹¹B NMR spectra of borate glasses can be accurately computer-simulated using a simple model for the electric field gradient at a boron site in the BO₃ and BO₄ structural units, assuming these structural units are relatively undistorted. Deviations from the average OBO bond angle in these two sites are determined from the simulations to be less than ± 2° in borate glasses. There is no evidence for increasing distortion in the fundamental structural units with increasing metal oxide content.     

Copper in Coloradoite,HgTe: Actual State or Analytical Artifact?

Crystallography Reports - Chemical and structural data of two Cu-rich coloradoite crystals from Kalgoorlie, Australia, are reported. Two grains with simple stoichiometries, i.e.,...     

Electronic structure of arsenic chalcogenide glasses by extended Hückel theory

The electronic structures of arsenic chalcogenide glasses are investigated by the extended Hückel theory which is a simple one-electron LCAO approach. The density of the valence state (DOVS), the optical gap and the imaginary part of the dielectric constant are calculated and found to agree roughly with those observed. Further, the changes in them due to various structural changes are calculated to explain the pressure dependence of the optical gap, the change of DOVS caused by a structural change induced by high pressure and the difference between the DOVSs for the as-deposited and the well-annealed film.     

Contribution to High-temperature Modifications of the Anhydrous Alkaline Earth Metal Sulfates

Large synthetic crystals of alkaline earth metal fluorides, especially fluorite crystals, contain sometimes unknown small inclusions of hexagonal form. Samples of these crystals were investigated by microscope, X-ray, and microprobe analysis to identify the included small crystals. Optical behaviour of these inclusions, morphology, chemical composition, and the reaction with water allow their interpretation as high-temperature modifications of the anhydrous water soluble alkaline earth metal sulfates, partly transformed to the corresponding sulfides.     

Formation and stability of amorphous molecular systems: As the prototype of functional amorphous organic materials

Structural changes in vapor-deposited amorphous states of simple organic compounds were studied by Raman scattering, X-ray diffraction, and light interference in the sample. Two types of processes, namely direct crystallization and structural relaxation leading to glass transition, were observed depending on the flexibility of the molecule. Gradual relaxations were also found to occur in amorphous states of butyronitrile and 1,2-dichloroethane at temperatures much lower than their T_g or crystallization temperature. The observed structural changes are discussed by referring to the high enthalpy of the vapor-deposited amorphous systems.     

New lead-fluorozirconate glasses containing BIF3

New lead-fluorozirconate glasses in the system ZrF₄–PbF₂–BiF₃ were investigated. The stabilizing effect of BiF₃ on the binary system ZrF₄–PbF₂ glasses was established. A complete investigation of this system allowed us to obtain samples of up to 3 mm in thickness. Its further optimization was achieved by introduction of other fluorides resulting in increased resistance to devitrification. Thermal and optical data are reported.     

Reflection Splitting in RHEED Investigations of Vacuum Evaporated GaAs Layers

RHEED-diagrams of vacuum deposited GaAs-films with high density of structural defects often show splitting of matrix reflections into satellites. It can be shown by simple models, for example of {111}-oriented films, that this phenomenon is originated by formation of stacking faults perpendicular to 〈ĪĪĪ〉-B growth directions of the films. The conditions for 〈110〉 and 〈211〉 azimuths are discussed.     

微孔氟化磷酸镓Ga3P3O12F·0.5(1,8-C8H22N2)的水热自组装与晶体结构

采用水热合成法制备了一个三维微孔氟化磷酸镓Ga3P3O12F·0.5(1,8-C8H22N2)(简称Hit-6).反应起始原料摩尔配比为∶GaOOH∶H3PO4∶HF∶1,8-辛二胺∶H2O=1∶2∶1∶1∶555.Hit-6的骨架是由Ga3P3六聚体结构单元通过共顶点联接构成三维纳米孔结构,在[101]方向呈现8-元环孔道.     

Phase fronts at the NaNbO3P-⇌ NaNbO3 R phase transition

The structural phase transition between phase P and phase R in NaNbO₃ single crystals was studied by an optical method. It was found that this transition is similar to the martensitic transformation and that the phase fronts are formed by crystallographic planes having indices close to {0.2.11}. Behind the simple phase front a monodomain state arises. The polydomain state is the resultant of complex phase fronts.     

Thermal Expansion of SrF2 at Elevated Temperatures

The X-ray method was used to determine the linear thermal expansion coefficient of SrF₂ in the temperature range from 301 to 1173 K. A comparison of the thermal expansion coefficients of CaF₂, SrF₂ and BaF₂ at T > 300 K shows that the degree of lattice an–harmonicity in the alkaline earth fluorides decreases with increasing mass of the alkaline earth atom. The results for the thermal expansion of SrF₂ are used to discuss the temperature dependence of the lattice mismatch in the SrF₂/InP film–substrate system.     

Investigation of multicomponent fluoride optical materials in the UV spectral region: I. Single crystals of Ca1−x R xF2+x (R = Sc, Y, La, Yb, Lu) solid solutions

Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca_1?x R _xF_2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region.     

Effects of mixed alkaline earth oxides additive on crystallization and structural changes in borosilicate glasses

The effects of mixed alkaline earth oxides on crystallization and structural changes in a multi-component borosilicate glass system are studied by using X-ray diffraction (XRD) and transmission electron microscope (TEM). It is found that the crystallization is decreased with increasing alkaline earth oxide content and there are also a series changes occurred in TEM images. This paper introduces the conception that alkaline earth ions tend to occupy their preferred sites regardless of glass systems. This conception is assisted to explain the TEM images to some extent by suggesting a simple structural model about non-bridging oxygen in glass network. The conception also indicates a ‘blocking effect’ existing in such a multi-component borosilicate glass system, which may be responsible for XRD results in chief. In addition, the structural model suggested by TEM results refers a new unit of Si–O–M²⁺–O–B, which helps in understanding the minimum exhibits in XRD results. Moreover, a dielectric test is taken to study glass properties in detail.