Zur Kristallographie der martensitischen ε → α-Gitterumwandlung

Many iron and cobalt alloys transform to the martensitic reaction γ → ε → α. The platelets of the hex. ε-martensite are very thin. Thus the growth of the crystals is limited in the direction [0001]_ε and the transformation ε → α can be treated as a plane problem. Metallographic investigations demonstrated the size, form and orientation of the α-crystals after cooling without and with external tension. On the basis of connection of the hex. and the bcc. lattice formulae are discussed of the directions of the lattices, and the changes of the volume and the shape, resp.     

Bildung und Untersuchung von SixAl1−xAs-Kristallen

Si_xAl_1−xAs is formed by chemical transport reaction of AlAs using iodine as transporting agent. The experiments are performed in sealed silica tubes in the temperature range from 900 to 1000°C. The grown platelet-shaped crystals and whiskers are investigated with x-ray diffraction, light microscopy, electron microscopy and electron-probe microanalysis. The mechanism of growth is discussed.     

The crystal and molecular structure of 5α,8α-epidioxyergosta-6,22-dien-3β-acetate

From the mushroom species Tricholoma populinum LANGE which shows interesting pharmaceutical effects the steroid 5α,8α-epidioxyergosta-6,22-dien-3β-ol has been isolated. The acetate of this compound crystallizes in the monoclinic space group P 2₁ with two molecules in the unit cell of dimensions a = 19.788, b = 7.241, c = 9.914 Å, β = 103,97°. The final R-value is 0.079 for 1082 reflections.     

Crystal and Molecular Structure of 6α-Methyl-3,20-Dioxo-5β-Pregnan-17α-yl Acetate

The title compound 6α-methyl-3.20-dioxo-5β-pregnan-17α-yl acetate crystallizes in the monoclinic space group P 2₁ with two molecules in the unit cell and the lattice parameters a = 10.889, b = 11.056, c = 9.8029 Å, β = 101.51° The crystal structure is isostructural with medroxyprogesterone acetate and refined by full matrix least squares calculations up to the discrepancy factor R = 0.051.     

3 β ‐Acetoxy‐5 α ‐cholestan‐6‐one: A Steroid

The crystal and molecular structure of 3 β ‐Acetoxy‐5 α ‐cholestan‐6‐one has been determined by X‐ray crystallographic techniques. The compound crystallizes in the space group P2₁ with cell parameters : a = 13.060(3), b=6.299(2), c=17.152(6)Å; β =96.47(3)o, V = 1402.02ų, Z = 2, R = 0.072 for 1921 observed reflections. The six‐membered rings (A, B and C) exist in the chair conformations while the five‐membered ring‐d assumes half‐chair. All rings of the steroid skeleton are trans connected.     

Untersuchung der Korngrenzendiffusion von Zn-65 in α-Aluminium-Zink-Legierungen

The diffusion of Zn-65 in large angle grain boundaries in Al and in 8-Al Zn alloys was investigated. p_K = γδD_K rises exponentially up to a Zn content of 7 at-%, then at a lower rate with concentration. Above 40 at-% Zn p_K is almost independent of concentration. At the solidus temperature, D_K is of the order of 10⁻⁵ cm²/sec. A simple vacancy model for the diffusion in large angle grain boundaries is being discussed. From the model, the following parameters for the grain boundary self diffusion in Al and Cu that have not been investigated so far can be estimated: The activation energies for the electromigration in thin polycrystalline Al films and for the superplasticity at the eutectoid composition are compatible with the results of this investigation. The kinetics of the discontinuous precipitation and the eutectoid transformation in Al Zn alloys is governed by the phase boundary diffusion.     

Synthesis of spindle‐shaped α‐FeOOH and α‐Fe2O3 nanocrystals

Spindle‐shaped α‐FeOOH nanocrystals were facilely synthesized using a poly (vinyl pyrrolidone) (PVP)‐assisted route under hydrothermal conditions. The chemical compositions and morphol‐ogies of the as‐prepared samples were characterized in detail by X‐ray power diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The experimental results reveal that these spindle‐shaped α‐FeOOH nanocrystals have self‐organized into assemblies with hierarchical nanostructures. The crucial roles of PVP in the hydrothermal synthesis of hierarchical α‐FeOOH nanostructures were discussed. The possible formation mechanism was also suggested. Moreover, the spindle‐shaped α‐Fe₂O₃ nanocrystals could be easily obtained after calcining the α‐FeOOH prepared by the PVP‐assisted hydrothermal process. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallographic Investigations of 3β‐acetoxy‐5α‐cholestan‐6‐one‐semicarbazone ‐ A Steroid

The crystal structure of 3b‐acetoxy‐5a‐cholestan‐6‐one‐semicarbazone (C₃₀H₅₁O₃N₃) has been determined by X‐ray diffraction methods. It crystallizes in the orthorhombic space group P2₁2₁2₁ with cell parameters a = 11.641(1), b = 16.552(1) c = 31.181(4) Å and Z = 8. The structure has been refined to an R‐value of 0.050 for 4407 observed reflections. Two molecules in the asymmetric unit have been observed. In both the crystallographically independent molecules, all the three six‐membered rings (A, B and C ) of steroid nucleus exist in chair conformation, while the five‐ membered ring D exists in 13β distorted‐envelope in molecule‐I and 13β, 14α half‐chair conformation in molecule‐II. Three intermolecular N‐H … O hydrogen bonds have been observed.     

Photochrome Eigenschaften von γ-bestrahlten Claciumfluoridkristallen mit Lanthan-Dotierung

The preparation of La-doped CaF₂ crystals is described. Their photochromic properties in the UV and visible spectral range are investigated. Furtheron their use for information storage is discussed and their capacity compared with the reported characteristics of additively coloured crystals.     

Zum Nachweis von Versetzungen in β-Kupferphthalocyanin-Einkristallen

An etching technique was developed to investigate dislocations in β-copper phthalocyanine single crystals. Considering the expected content of dislocations and the etch pit symmetry the symmetric etch pits are correlated to [010]-edge dislocations on {201 }- and {001}-lattice planes with (001)- and (201 )-slip planes. Asymmetric etch pits on {001}- and {201 }-planes are connected with [010]-edge dislocations related to (100)- and (101 )-slip planes. The dislocation density on growth planes and cleavage planes is commonly lower than 100 cm⁻². [010]-screw dislocations are not observed, but their existence could not be excluded.     

Zur Gleichgewichts- und Wachstumsform von β-Kupferphthalocyanin-Einkristallen

The equilibrium shape of β-copper-phthalocyanine single crystals is obtained by the method of the PBC-vectors according to HARTMAN and PERDOK . These results agree well with the experimentally found growth shape of single crystals grown in the vapour phase. The crystals are of needle-like shape. The crystal surfaces are lattice planes of the kind {001}, {201 }, {100}, {101 } and {110}. The ratio of length to width of the crystals is influenced by the inert gas pressure during the growth process. This dependence is caused by the diffusion of the nutrient.     

The effect of impurities on the β → α transformation process in tin

This article presents data on the impurities influencing the β → α transformation of high purity tin (99.9995%): temperature of the α → β transition-T₀, nucleation and α-crystal growth.     

On the coexistence of phases at the α–β transition in quartz

The character of the α–β transition in crystals of natural and synthetic quartz has been studied by measuring the refractive index. The coexistence of two different crystallographic modifications over some temperature range has been established. The α–β phase transition is supposed to be attributed to the near-critical phase transitions. In synthetic quartz with Al and Fe structural impurity the α–β transition consists of two successive transitions. First the transition from the α-phase to an intermediate one takes place, then the intermediate phase is transformed into the β-Phase. Within a certain temperature range there exists only the intermediate phase.     

Characterization of α and γ polymorphs of glycine crystallized from water‐ammonia solution

Crystallization of metastable α and stable γ polymorphs of glycine was carried out from aqueous solution in the presence of ammonia. Pure aqueous solution and solution with lower concentration of ammonia yield α nucleation and solution with a critical concentration of ammonia yield γ nucleation. Variation in the solubility of glycine in double distilled water and pH of the resulting solution due to the ammonia incorporation was studied in a range of temperatures. The induction period for the α and γ nucleation in the solution was determined and its variation due to the ammonia incorporation was also studied. Single crystals of both the polymorphs were grown by slow evaporation method. Effect of ammonia concentration and the resultant pH of the solution on the nucleation, growth and morphology of the grown polymorphs were investigated. The unidirectional growth of the γ polymorph along the polar axis was revealed. X‐ray powder diffraction method was employed to distinguish both the polymorphs structurally. Their thermal stability above room temperature was studied by differential scanning calorimetry which revealed that the as‐grown γ polymorph transforms to α at 179.6 °C while the as‐grown α retains its phase until melting. The optical transmittance of the grown γ polymorph was studied in the UV‐Vis‐Near IR region. The second harmonic generation (SHG) efficiency of the grown γ polymorph was studied with a Nd:YAG laser source and is about 6.8% higher than that of the inorganic standard KDP. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bildung von paramagnetischen Defekten in SiO2-Glas nach Oberflächenbehandlung im Niederdruckplasma

Low pressure plasma treatment of SiO₂-glass produces paramagnetic defects in SiO₂ volume. The defects are similar to those created in quartz (glass or crystal) by neutrons or γ-radiation. As a cause of defect formation taking place only in glassy and not in crystalline samples plasma radiation is proved. From dependence of defect concentration on conditions of formation (plasma parameters, time of treatment) a complex mechanism of formation will be concluded. The depth distribution of defects refers to their diffusion in SiO₂ volume.     

Mechanism of nucleation and growth of crystals under α → β transformation of tin

This article presents data on the mechanism underlying the nucleation and growth of α-Sn crystals in mono- and polycrystal β-Sn tin. It is demonstrated that the low temperature deformation and thermocycling (subjection to the cyclic changes of temperature) of the samples of tin (99.9995% Sn) brings to the increase in the α-Sn crystal nuclestion rate. Kinetics of the nucleation is characterised by the presence of the non-steady State period t_n. On analysing the temperature dependencies of the rate of the α-Sn centre growth obtained for the planes (100), (001) and (110) it was shown that the mechanism of movement of the interphase boundary depends on the value of the motive force ΔF.     

The Morphology of Some Hydrothermally Synthesized Li-Minerals: A-Zeolite, α-Eucryptite, β-Spodumene and β-Eucryptite

The hydrothermal treatment of glass with the composition 2 LiF, Al₂O₃, 3 SiO₂ at 1 kbar in the range of 150 °C to 850 °C gave rise to the formation of A-zeolite with orthorhombic unit cell with å = 10.31 Å/b̊ = 8.18 Å/c̊ = 5.0 Å (space group Pna2₁), α-eucryptite, trigonal, å = 13.4 Å/bº = 13.4/Å/cº = 9.0 Å (space group R 3 ), β-spodumene, pseudocubic/tetragonal, å = 7.53 Å/b̊ = 7.53 Å/c̊ = 9.15 Å (space group P4₃2₁2), β-eucryptite, monoclinic, å = 7.75 Å/b̊ = 5.2 Å/c̊ = 11.16 Å (space group P6₂22). The morphology and development of the mineral phases depend on the temperature of formation.     

Crystal structure of 4-(2-hydroxyethyl)-4-aza-5α-androstan-17β-ol “HS-478”

The crystal structure of HS-478 (aqueous solvate) has been determined by direct method and refined by block diagonal least squares to R₀ = 0.043. The intensity was measured in a four-circle diffractometer in the ω/2θ scanning mode, CuKα radiation. The crystals are triclinic P1, a = 6.721(3), b = 66.532(3), c = 12.188(5) Å, α = 96.86(2)°, β = 82.82(2)°, and γ = 114.68(2)°. Rings A, B, C are chair whereas ring D is envelope. Rings A/B and B/C are trans fused, whereas rings C/D are quasi trans. The hydroxyethyl side chain connected to N(4) has conformation of (−t, t).