X‐ray Rotation‐Tilt‐Method — First Results of a new X‐ray Diffraction Technique

That from us as X‐ray Rotation‐Tilt Technique (XRT Method) designated procedure principle represents a world innovation and overcomes essential disadvantages of comparable diffraction techniques known up to now. Starting from the origin and the informational content of the XRT interferences a realization of a special equipment and selected examples of some first applications are presented.     

Synthesis,Crystal Structure and Charge Distribution of InGaZnO4. X‐ray Diffraction Study of 20kb Single Crystal and 50kb Twin by Reticular Merohedry

Synthesis of InGaZnO₄ at 20Kb and 50Kb produced a single crystal and a twinned crystal respectively. The X�ray diffraction crystal structure refinement (R1 = 0.015 and 0.019 respectively) and the Charge Distribution analysis are reported. Space group is R3m; cell parameters in hexagonal axes are a = 3.2990(2)Å, c = 26.1013(25)Å (20kb single crystal) and a = 3.3051(2)Å, c = 26.1029(19)Å (50kb twinned crystal). The cell volume is 246.01(3)ų and 246.94(3)ų respectively. The In is in regular octahedral coordination, whereas Ga/Zn are in trigonal bipyramid co‐ordination. Charge Distribution on cations (2.94 and 2.95 respectively vs. 3.0 for In, and 2.53 vs. 2.5 for Ga/Zn) shows that the structure is well refined. Charge Distribution on oxygens (—1.96 and —2.04 for O1 and O2, vs. —2.0) excludes the presence of valence unbalance effects. A possible structural role of the trigonal bipyramidal coordination is discussed.     

Composition Dependency of Lattice Anisotropy of TlBX2‐type Chain Mixed Crystals

Variation of the lattice parameters of TlTl_1‐xIn_xSe₂ chain mixed crystals with composition have been studied by X‐ray diffraction technique. The lattice anisotropy ( c/a ) of the TlBX₂‐type mixed crystals changes linearly with substitution of the atoms located both at the center and at the vertices of the BX4 tetrahedra. A brief survey of the important features of the effect of isomorphic atom substitution on the lattice anisotropy of TlBX₂‐type mixed crystals with chain structure has been presented.     

Crystal Structure of 6, 6' ‐ Dihydroxy ‐ 2, 2' ‐ biphenyl ‐ 19 ‐ crown ‐ 5 ; Comparison of Some Structural Features among Related Ligands and Compounds

It has been determined the crystal structure of 6,6'‐dihydroxy‐2,2'‐biphenyl‐19‐crown‐5, C₂₂H₂₈O₇ (1a). Likewise, it has been set up a comparison between the results and some features of this structure obtained by molecular mechanics calculations. Due the presence of a hydrogen bond, the crown oxygens have not a geometrical disposition to lead its electronic pairs into the cavity and therefore the system complexation constant decreases, compared to some related ligands and compounds.     

Crystallographic Analysis of Acetyl β ‐boswellic acid

The crystal structure of the title compound (3 α ‐acetoxy‐urs‐12‐en‐24‐oic acid, C₃₂H₅₀O₄) has been determined by X‐ray crystallographic techniques. The compound crystallizes into orthorhombic space group P2₁2₁2₁ with unit cell parameters : a = 12.773(2), b=16.381(4), c=27.929(7)Å. The structure has been solved by direct methods and refined to R = 0.054 for 4930 observed reflections. The structure contains two crystallographically independent molecules in the asymmetric unit which are almost identical in geometry. Rings A, B, D and E have chair conformations while ring C assumes a sofa conformation in both the molecules. The molecules in the structure are linked together by intra‐ and intermolecular O‐H…= and C‐H…O hydrogen bonds.     

Crystal and Molecular Structure of bis[diaaqua(1H‐cyclopenta(2,1‐b:3,4‐b')(dipyridine ‐2,5‐dione))N ickel(II)]dihydrate

The title compound [Ni(CPDD)(H₂O)₂]₂(H ₂O )₂, {]Ni₂(C₄₄H₂₈N₈O₁₂)] (H₂O)₂ }, where CPDD = 1H‐cyclopenta(2,1‐b:3,4‐b')(dipyridine‐2,5‐dione) has been prepared and its crystal structure determined by single crystal X‐ray diffraction at room temperature. The complex crystallizes in the triclinic space group P1 w ith two molecules in the asymmetric unit. The cell dimensions are a=10.452(1),b=14.098(1) & c=16.023 Å; D=110.13(1), E=100.63(1) & J=100.85(1)°. The two independent molecules in the asymmertic unit are related by pseudo two fold symmetry. In both the molecules the coordination environment around the Ni(II) may be best described as a distorted octahedral. Due to some delocalization of charge towards one of the oxygens(O1a) from the O2a atom some degree of bond localization has been observed. The individual diones of both the molecules are almost right angles at the metal atom. A long the y‐axis inversion related molecules are forming pseudo‐dimers through hydrogen bonding.     

A Polymorph Crystal Structure of Hexaphenyl Observed in Thin Films

Highly oriented thin films of hexaphenyl — which are used in organic opto‐electronic applications — are characterised in terms of their crystal structures. Two different crystal structures of hexaphenyl (C₃₆H₂₆) are observed when the films are prepared by physical vapour deposition at various substrate temperatures. If the substrate is kept at room temperature, hexaphenyl crystallises within a structure which is already known from single crystal investigations. However, when the thin films are grown at a substrate temperature of 160°C a new crystalline phase appears. This structure was characterised by X‐ray and transmission electron diffraction. Due to the strong preferred orientation of the crystallites within the thin films, the lattice constants as well as main features of the new crystal structure could be determined. The lattice is indexed as monoclinic with: a = 7.98Å, b = 5.54Å, c = 27.64Å and β = 99.8°. The new crystal structure has high similarity to the already known crystal structure: Both structures are built by layers of hexaphenyl molecules, within one layer the aromatic planes of the hexaphenyl molecules are packed in a herringbone pattern. The characteristic feature of the new structure is that the long axes of the hexaphenyl molecules are arranged absolutely perpendicular to the layers, whereas, within the already known structure the long axes show an tilt angle of 17° to the layer normal direction.     

Quantitative Phase Analysis of Mixtures of Three Components using Rietveld and Rius Standardless Methods. Comparative Results

Eight samples, supplied by the Commission on Powder Diffraction of the International Union of Crystallography, through the Round Robin on quantitative phase analysis, were analized using standardless methods. Samples were mixtures of corundum, zincite and fluorite in different ratios. The Rietveld method, using the DBW 3.2 and FULLPROF software, and the Rius method, using MENGE‐PC software, were used. Results obtained agree well with the real composition supplied (a posteriori) by the IUCr.     

Crystal and Molecular Structure of Desmodin

The crystal structure of the title compound has been determined from X‐ray diffraction. The compound crystallizes from benzene in the orthorhombic system, space group P2₁2₁2₁, with unit cell parameters: a = 8.485(2), b = 9.816(2), c = 22.597(4) Å, Z = 4, V = 1881.9(7) ų. The structure was determined by direct methods and refined to a final R‐factor of 0.04. Six membered rings B and E are planar. Ring A and ring C are in slightly distorted sofa conformation. Ring D is in envelope conformation. The structure is stabilised by weak intermolecular C‐H...O hydrogen bonds.     

Phase Formation and Solid State Structure on Calcination of a Nickel Ferrite Acetate Precursor

The thermal decomposition of a freeze dried Ni‐Fe‐μ‐oxo‐acetate results in the formation of an amorphous nickel ferrite. Crystallization of the spinel NiFe₂O₄ takes place between 300 and 500°C. High disperse amorphous (or less crystalline) products with specific surfaces up to 500 m²/g can be obtained by carful decomposition between 260 and 300°C. Raising the calcination temperature and calcination time effects a decrease of porosity and of the specific surface. The primary nanocrystalline spinel powder is strongly agglomerated. During an annealing process between 300 and 500°C the crystallite size is increased but the mean diameter of agglomerates of about 15 μm does not change. A combination of milling and ultrasonic dispersion allows the adjustment of grain sizes < 1 μm with a narrow grain size distribution.     

Growth and Characterisation of (CuInTe2)1‐x(2 ZnTe)x Solid Solution Single Crystals

The crystal structure as well as the optical properties in the band gap region of (CuInTe₂)_1‐x(2 ZnTe)_x solid solution single crystals grown by directional freezing have been studied. The lattice constants exhibit a linear dependence on crystal composition. The chalcopyrite‐sphalerite phase transition was observed between x = 0.3 and x = 0.4°. The variation of the band gap with respect to crystal composition can be described by a quadratic expression.     

Crystal Structure of Spiro[2‐benzoyl‐cyclohexyl‐4,5‐diphenylpyrrolidine‐3,3'‐chroman‐4‐one]

3‐Phenyl‐chroman‐4‐one is the basic unit of isoflavonoids which are found in the plants of the sub‐family papilionoidae of Leguminosae. They are known to possess antifungal and antibacterial properties. Crystal data of the title compound : Monoclinic, space group P2₁/c, a = 14.021(3), b = 18.682(4), c = 11.362(2) Å, β = 95.75(3)°, R = 0.066. The two phenyl rings directly attached to the pyrrolidine ring are nearly perpendicular to it. The dihydropyrone moiety adopts a half‐chair conformation while the cyclohexane ring attached to the pyrrolidine ring adopts a chair conformation. The best plane passing through the chroman‐4‐one moiety makes a dihedral angle of 82.2(3)° with the pyrrolidine ring. The molecule is stabilized by one intra‐ and two intermolecular C‐H...O hydrogen bonds.     

Estimation and Correction of Effects of Simultaneous Reflections on Intensity Data Collected with the Four‐Circle Diffractometer

A procedure based on the kinematical theory has been developed to estimate and correct the effects of simultaneous reflections on intensity data collected with the four‐circle single crystal X‐ray diffractometer through minimizing the scatter of the corrected structure factor (intensity) values of equivalent reflections.     

Optical characterization and crystal structure of the novel bronzetype CaxBa1‐xNb2O6 (x = 0.28; CBN‐28)

Calcium barium niobate (CBN), also like strontium barium niobate (SBN), belongs to the materials family of partially filled tetragonal tungsten bronzes, which show relaxor‐type ferroelectric phase transitions and large electro‐optic effects. For the first time, it was possible to grow large single crystals of Ca_0.25Ba_0.75Nb₂O₆ (CBN‐25) and CBN‐28 by using different growing techniques. The successful single crystal growth allowed to investigate several physical properties of the novel phase. Herein, we report on measurements of differential thermal analysis (DTA), wavelength dispersion of the refractive indices, temperature dependence of the birefringence and light absorption. Additionally, results of the single crystal X‐ray structure analysis are presented.     

On the effects of Ga3+ and La3+ ions in MgCu ferrite: Humidity‐sensitive electrical conduction

Pure and gallium or lanthanum substituted MgCu ferrites, Mg_0.5Cu_0.5Fe_2‐xM_xO₄ (with x = 0 or 0.2 and M = La or Ga) have been prepared by solid state reaction. Sintering experiments were carried out at different temperatures between 900 and 1100°C. The phase composition and lattice parameters were determined by XRD, while the effect of Ga and La substitutions on the granular structure was studied by SEM. Experimental results revealed that the densification behaviour and some physical properties are in close relation with the structural changes of pure ferrite caused by the presence of La and Ga substitutions. The gallium containing compound, Mg_0.5Cu_0.5Fe_1.8Ga_0.2O₄, is monophasic and contains a great number of pores, whereas the lanthanum containing compound, Mg_0.5Cu_0.5Fe_1.8La_0.2O₄, is biphasic and exhibits a high density. The humidity characteristics show that the gallium ion enhances the humidity sensitivity of the MgCu ferrite sintered at 1000°C. This interesting effect is promising for the future of the Ga‐substituted MgCu ferrite to be used as sensitive material for fabrication of ceramic humidity sensors. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of X‐ray Satellite Reflections Attributed to Antiphase Boundaries in Epitaxial (Ga,In)P Layers grown on (001) GaAs Substrates

We report on the analysis of additional X‐ray reflections that probably arise from antiphase domain boundaries within (Ga,In)P/(001) GaAs heteroepitaxial layers. Due to the preferred cation ordering along the crystallographic directions [1‐1 1] and [‐1 1 1] which belong to the [110] zone the original sphalerite‐type structure of (Ga,In)P changes into a CuPt‐like of the cation sublattice. This ordering phenomenon causes a loss of symmetry, i.e. the cubic structure is converted into a rhombohedral one. The antiphase boundaries between ordered domains are assumed to behave similar to lattice planes at X‐ray diffraction. Therefore, additional reflections may occur spatially neighboured to the [001] direction. The presented results of X‐ray experiments are discussed in relation to TEM experiments published in the literature in order to explain the origin of the satellite reflections. In the case of the investigated samples (grown on GaAs substrates misoriented 2° towards the azimuthal [010] direction) the APBs run preferentially in directions tilted up to angles of 20° with respect to growth direction. A preferential occurrence of satellite reflections in <13 2 1> directions was observed coinciding with {13 2 1} "lattice planes" whose normals enclose the same angle to the [001] growth direction as the normals of the average planes characterized by APBs. The appearence of the phenomenon in other directions that are also spatially neighboured to the <13 2 1> directions was determined on the basis of the shift of the reflection positions due to tilting the sample around an axis geometrically included in the scattering plane.     

Crystal Structure of Diethyl 2‐[2,2,2‐ trifluoro‐1‐(indole‐3‐yl)‐ethyl]‐2‐acetamidomalonate

The title compound (C₁₉H₂₁F₃N₂O₅) has been determined from three dimensional X‐ray diffraction data. The crystals are monoclinic, a = 7.626(4)Å, b = 17.515(4)Å, c = 15.066(3)Å, β = 101.02(3)°, V = 1975(1)ų, Z = 4, D_calc = 1.393g cm^‐3, space group P2₁/c. The structure was solved by direct methods and refined by full‐matrix least‐squares method (R = 0.039).     

Crystallographic shear defect in molybdenum oxides: Structure and TEM of molybdenum sub‐oxides Mo18O52 and Mo8O23

Molybdenum trioxide and molybdenum sub‐oxides are of great interests in catalysis due to their utilities as model system to elucidate the correlations between the structure and the catalytic performance. The suboxides are usually an intermediate phase during catalytic reaction in which the lattice oxygen is involved. We show the identification of the two common molybdenum sub‐oxides Mo₁₈O₅₂ and Mo₈O₂₃, derived from MoO₃ by crystallographic shearing (CS), by means of electron diffraction and High‐Resolution Transmission Electron Microscopy (HRTEM) in combination with image simulation. The coincidence of simulated electron diffraction patterns and high‐resolution images with the experimental ones indicates the feasibility of CS structure determination by these techniques.     

Crystal structure of 2‐(3‐amino‐2,4,4‐tricyano‐buta‐1,3‐dienyl)‐ thiophene

The title compound (C₁₁H₆N₄S) crystallizes in the orthorhombic space group Pbca with a = 23.561(4) Å, b = 7.064(1) Å, c = 13.018(3) Å, Z = 8; D_x = 1.387(1) g.cm^‐3 ; R = 0.073 for 1697 observed reflections [F2 ≥ 2σ(F²)]. The interesting feature is disorder in the crystal structure resulting from the existence of two isomeric molecules with interchangable carbon and sulfur positions, occuring at random but with equal probability in the structure.