Structure types – a review

Structures of binary inorganic A_xB_y compounds with A and B on two Wyckoff positions are characterized by the self‐coordination numbers T_i, i = 1–3, of A and B atoms. The T₁ = 0–12 values of 122 structure types can be correlated with different topologies, A–A interactions and densities. High T₁ values like T₁ = 12 are obtained for fcc or hcp sphere packing with maximum density of A atoms and interstitial B atoms. Hexagonal or tetragonal layered compounds are recognized by the T_i values 6 6 6 or 4 4 4. The T₁ = 2 values are found for chains, T₁= 1 for ordered molecules like N₂ or Br₂. The A and B atoms of few compounds like NaCl or CsCl form a pc or bcc sphere packing. The T₁ = 0 values of Na or Cs atoms indicate repulsive Na–Na or Cs–Cs interactions. Distorted structures of a structure type are recognized, if atoms with slightly different A–A or B–B distances are included in the proper coordination shells. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of phase equilibria and heterojunctions in Ga–In–As–Sb quaternary system

The phase diagram of the Ga–In–As–Sb quaternary system has been determined experimentally and also has been treated on the base of thermodynamic calculations. The liquidus data were obtained by DTA and solidus data were determined using electron microprobe analysis on LPE-layers of Ga_xIn_1–xAs_ySb_1–y on GaSb and InAs substrates. Isolattice-parameter heterostructures prepared on these substrates were free of mismatch dislocations and suitable for application to light-emitting diodes and semiconductor lasers.     

Phase Equilibrium of the Ga–Al–Sb system

Employing the method of liquid-phase epitaxy (LPE) solid-solutions of Ga_1–xAl_xAl_xSb (0 ≦ x ≦ 0.8) have been obtained. The dependence of Sb solubility on Al concentration in the liquid phase at 403°C, 452°C, 500°C has been established. The dependence of AlSb concentration in the solid phase on the composition of the liquid phase has been investigated at 452°C. Using the chemical constants equilibrium method, the phase equilibrium of the Ga–Al–Sb system in the region of liquid phase composition near the Ga-rich corner of the phase diagram has been calculated. The comparison of experimental and calculated data for the liquid and solid phases shows their agreement within the limits of experimental error.     

Crystal structure of R(–)–1–Tosyl–2–methylpyrrolidine

The crystal structure of R(–)-1-tosyl-2-methylpyrrolidine has been determined by X-ray structure analysis. The compound crystallizes in the monoclinic space group P2₁ with cell parameters a = 7.858(1), b = 14.929(6), c = 11.128(1) Å, β = 105.42(1)°. The structure has been solved by direct methods and refined to R = 0.046. There are two crystallographically independent molecules A and B in the asymmetric unit. The pyrrolidine ring of molecule A is disordered with atom C4 occupying two possible sites. The S atom has a distorted tetrahedral coordination in both the molecules. Two bifurcated hydrogen bonds are observed. Molecules are held together by hydrogen bonds.     

The Dielectric and Optical Properties of the Homologous Series of Cyano-Alkyl-Biphenyl Liquid Crystals

The electric permittivities, refractive indices and densities of the homologous series of alkyl-cyano-biphenyls (C_nH_2n+1.φ.φ.CN) have been measured as a function of temperature in the nematic phases for n = 5 to 9, and in the smectic phases for n = 8 and 9. The results have been analysed in terms of the Maier and Meier theory to yield values for the molecular dipole moments and polarizabilities. Kerr effect measurements on dilute solutions of 44′-n-pentyl-cyano-biphenyl at different temperatures are reported, and in conjunction with similar dielectric and optical measurements have provided results for the free molecule dipole moment and polarizabilites; values for the higher homologues are predicted using a bond additivity model. Bordewijk's theory is applied to the permittivity measurements, and using appropriate molecular parameters, dipole-dipole correlation factors are calculated.     

Study of InxGa1–xP/GaAs Films Formation on the Basis of In–Ga–P Liquidus Precised Investigation

It is shown that the In–Ga–P melt which is prepared by contacting with the GaP seed becomes supersaturated in reality. Some peculiarities of In_xGa_1–xP/GaAs films formation at quasi-equilibrium conditions are described. It is observed that the saturated In–Ga–P melt dissolves the GaAs substrate when isothermally contacting if the In_xGa_1–xP equilibrium solid has the lattice parameter less than that of GaAs. As a result some InGaAsp deposit arises on the substrate. This phenomenon takes place if the In–Ga–P melt is just supercooled. This instability of the liquid-solid interface is explained on the basis of the relaxation theory of non-equilibrium liquid-solid contact which has been created by the author in previous papers.     

Double Salt Formation in the Cu(HCOO)2–Sr(HCOO)2–H2O System

The solubility in the Cu(HCOO)₂–Sr(HCOO)₂–H₂O system has been studied by the method of physico-chemical analysis at 25 and 50 °C. It has been established that two double salts are formed in the system: CuSr₂(HCOO)₆ · H₂O at 25 °C and CuSr(HCOO)₄ · 4 H₂O at 50 °C. The latter salt has not yet been described in the literature. It has been characterized by X-ray powder diffraction and DT and TG analysis. CuSr(HCOO)₄ · 4 H₂O crystallizes in the triclinic system with lattice parameters a = 12.376(6) Å, b = 13.394(4) Å, c = 11.508(6) Å, α = 93.38(3)°, β = 94.01(3)°, γ = 75.04(3)°. Dehydration proceeds in two stages.     

Crossover temperature (TCO) and temperature gradient of refractive indices and length to breadth ratio of 4O.m mesomorphic compounds – an optical study

Refractive indices as a function of temperature are measured in a number of liquid crystals which belong to the N-(p-n-butoxy benzylidene)-p-n alkyl anilines, 4O.m compounds of the famous Schiff’s base nO.m liquid crystal compounds with m = 4 to 10 and 12. The temperature gradient of refractive indices, dn_e/dT and dn_o/dT, of these compounds are estimated. It is well known that in the case of dn_o/dT, there exists a crossover temperature, T_CO, which exhibits an odd–even effect with the alkyl chain length as expected. Further, using the birefringence data, the length to breadth ratio, k, for these compounds is estimated, which shows not exactly even–odd effect but irregular change with the chain number. The results are discussed with the body of the data.     

Optical Properties of TGS Crystal with <Emphasis Type="Italic">L</Emphasis>-Valine Admixture

The thermal expansion and temperature and the spectral dependences of the refractive indices and birefringence of triglycine sulphate (TGS) crystals with a 5% L-valine admixture have been investigated. It is established that the introduction of L-valine weakens the temperature dependence of the refractive indices and the birefringence and thermal expansion of TGS crystals. The parameters of the Sellmeier formula, refractions, and electronic polarizabilities are calculated. The changes observed may be related to the increase in hardness of admixture-containing crystals, the decrease in the spontaneous polarization, the replacement of the refraction components of the valine bond, or the spontaneous electro-optic effect.     

Determination of refractive index and electronic polarisability of oxygen for lithium-silicate melts using ellipsometry

The refractive index of Li₂O–SiO₂ melts has been measured using the ellipsometer constructed for high-temperature use. Measurements were carried out on four samples having different compositions over a wide temperature range (1300–1800 K). The standard deviation for the values measured was within ±0.0005. Additions of Li₂O were found to cause increases of refractive index in the temperature range investigated. At Li₂O concentrations <25 mol% the refractive indices of the melts increased with increasing temperature, similar to SiO₂. However, this temperature dependence became smaller with additions of Li₂O and at Li₂O concentrations more than 30 mol% the refractive indices of the melts decreased with increasing temperature. The temperature dependence of the refractive indices has been discussed from those of the density and the molar electronic polarisability on the basis of the Lorentz–Lorenz equation. In addition, the electronic polarisability of oxygen derived from the molar electronic polarisability increased with increasing temperature in each melt, suggesting that the ionicity of oxygen increases as temperature increases. Furthermore, additions of Li₂O were found to cause increases in the electronic polarisability of oxygen, due to the formation of non-bridging oxygen ions.     

Phase transitions from density and order parameter from polarisabilities in symmetric dimeric liquid crystals

As a part of our systematic studies on liquid crystal dimers, we present in this article the nature of phase transitions across isotropic–nematic and nematic–smectic-A exhibited by DLCs, α,ω-bis-(4-n-alkylaniline benzylidene-4?-oxy) alkanes. Further, the orientational order parameter in the nematic phase of these DLCs are estimated from the molecular polarisabilities calculated using the experimental refractive indices and density results. The molecular polarisabilities α_e and α_o are obtained for the compounds using the above results for both Vuks and Neugebauer local field models applicable to nematic liquid crystal. α_e and α_o calculated in this way are used to obtain Δα. The polarisability anisotropy in the perfect order (absolute K) is calculated semi-empirically using the δ-function model developed by Lippincott et al. and molecular vibration method. The values of polarisability anisotropy for both local electric field models differ significantly. No criterion is known to decide which value is correct. To avoid the determination of uncertain α and Δα values considering different local field models, a simple procedure developed by Kuczynski et al. was used for evaluation of S, based solely on birefringence δn = (n_e-n_o) and this value of S is compared with those obtained from field models.     

Positronenannihilationsuntersuchungen zur Elektronenstruktur des Systems Pd1–xAgxHn unter besonderer Berücksichtigung von Kristallbaufehlern

From angular correlation measurements in the system Pd_1–xAg_xH_n and in Pd_1–xAg_x alloys after the desorption of H as well as in the recrystallized and deformed state the following conclusions are obtained: the observed change of the angular correlation curve of PdH_0,65 compared with Pd is caused by crystal lattice defects introduced during the absorption of H. For Pd_0.80Ag_0.20H_0.43 and Pd_0.60Ag_0.40H_0.20 such a deformation effect is not observed. The results for the alloys can be explained with the help of the band structure calculations of SWITENDICK .     

Dielectric Anisotropy and the Order Parameter of HXBBA

Abstract

Measurements of dielectric anisotropy (Δ?), refractive indices (n _e , n _o), birefringence (Δn) and density (ρ) have been made in the nematic and smectic phases of N(-p-hexyloxybenzylidene)-p-butylaniline (HXBBA). The results indicate that the various transitions are of the first order type except smectic B-smectic G, which may be a second order transition. The order parameter S has been determined using the isotropic internal field model (Vuks approach) and the anisotropic internal field model (Neugebauer's approach) and both the values agree fairly well. The dielectric anisotropy (Δ?) increases strongly in the smectic phases whle S increases only slowly. It is interpreted by an increase of dipole-dipole correlations.     

On the Density of Synthetic Glasses in the System Soda Melilite – Gehlenite/Ákermanite

The solid density has been determined at 25°C by hydrostatic weighing along the binary systems Sm–Ge₅₀Åk₅₀ and Sm–Ge₇₀Åk₃₀. The molar volume V decreases linearly with increasing mole fraction of Ge_mÅk_n, x_B, according to δV/δx_B = −5.08 cm³ mol⁻¹ and −4.40 cm³ mol⁻¹ for Ge₅₀Åk₅₀ and Ge₇₀Åk₃₀, respectively. The results enable the molar fraction x_B to be determined from density measurements with an absolute error of ±5 mol%.     

Growth of InAs1–ySby solid solutions for obtaining decreased lattice mismatch in the InAs-GaSb (AlxGa1–nSb) system

This paper presents the results of investigation of the technological conditions of LPE growth of InAs_1–ySb_y solid solutions on InAs substrates. It is shown that the chosen regions of composition of InAs_1–ySb_y solid solutions and experimentally determined technological conditions allow the obtaining of InAs_1–ySb_y solid solutions with lattice parameter values close to those of the Al_xGa_1–xSb (0 ≦ x ≦ 0.2) solid solutions.     

Growth of Heterostructures Based on InAs–AlxGa1–xSb

It is reported on the liquid phase epitaxial (LPE) growth of heterostructures on the base of InAs–Al_xGa_1–xSb. The paper includes the investigation of epitaxial layers of Al_xGa_1–xSb alloys on InAs substrates and results of experiments for the determination of optimum growth regimes.     

Effective electro‐optic coefficient of (1–x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

Refractive indices and effective electro‐optic coefficient γ_c of (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PZN‐xPT, x = 0.05, 0.09 and 0.12) single crystals were measured at 532 nm wavelength. Orientation and temperature dependences of the electro‐optic coefficient were investigated. Large electro‐optic coefficient (γ_c = 470 pm/V) was observed in [001]‐poled PZN‐0.09PT crystal. More importantly, γ_c of tetragonal PZN‐0.12PT is almost unchanged in a temperature range −20 ∼ 80 °C. The γ_c of PZN‐xPT single crystals are much higher than that of widely used electro‐optic crystal LiNbO₃ (γ_c = 20 pm/V). These results show that PZN‐xPT single crystals are very promising materials for electro‐optic modulators in optical communications.     

A study of a fast ionic conductor–Ag1−xCuxI

The Conductivity of AgI–CuI system has been studied. Two molar ratios of the system Ag_1–xCu_xI with x = 0.05 and 0.15 have been taken. The transition temperatures are observed with conductivity measurements.     

Determination of the Effective Vacancy Concentrations and the Vacancy Losses after the Quench of Al–Zn–Mg Alloys

On the basis of

• 1 the experimental observation of dislocation loops by means of TEM,
• 2 the conclusion from this that the concentration of vacancies in the dislocation loops exists at the cost of the vacancy concentration primarily present at T_q, and
• 3 the inversion of the decomposition kinetics of Al–Zn–Mg alloys found out by means of resistivity and microhardness measurements, the effective vacancy concentration c_v.eff being at disposal for the GP-zone formation was found out by means of the relation t_R,max (t_R,max being the time required to reach the maximum of resistivity) and the Arrhenius plot In t_R,max = f(1/T_q) of the isothermal resistivity measurements. From the comparison of c_v.eff with the theoretical V concentration at T_q it is possible to derive statements about the loss of vacancies during and after the quench through loop formation, building-in of vacancies in GP-zones and annealing of vacancies at lattice defects. From this comparison follows:
  • The ideal ZnV concentration at T_q (calculated by means of the Lomer equation) is sufficiently great to account for the effective vacancy concentration.
  • The part of c_MgV in the loss concentration is rising with increasing c_Mg.
  Both these statements support the hypothesis that the initial process of the decomposition in Al–Zn–Mg alloys is caused by the ZnV diffusion.

     

Structure of (dimethyl sulfoxide‐S){glyoxylic acid thiosemicarbazonato(2–)‐O,N,S }platinum(II)

A crystal of the title complex [Pt(DMSO)(GT)] ( 1a ), where H₂GT = glyoxylic acid thiosemicarbazone, has been characterized by X‐ray crystallography and its structure has been compared with that of the recently described cytotoxic complex [Pt(DMSO)(GT)]·DMSO (1). The crystal of 1a is monoclinic; space group P 2₁/n; unit cell dimensions: a = 7.3270(10), b = 10.313(2), c = 13.706(3) Å, β = 101.92(3)°; V = 1013.3(3) ų; Z = 4. The Pt(II) ion is approximately planar tetragonal coordinated by the carboxylato oxygen, azomethine nitrogen and thiolato sulfur atom of the doubly deprotonated H₂GT molecule, and the sulfur atom of DMSO. The two five membered chelate rings are almost coplanar. In distinct with 1 , the sulfoxide oxygen atom and thiolato sulfur atom are in gauche position. A system of hydrogen bonds of the type N–H···O involving the amino, carboxylato and sulfoxide groups links the complex molecules within the unit cells. The π ‐π stacking pattern between the chelate rings in 1a involves centrosymmetric pairs of complex molecules and differs from that in 1 . (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)