Mechanism of the 2H → 6H solid state transformation in SiC

Single crystals of 2H SiC transform directly into the 6H (ABCACB) structure when the transformation nucleates at temperatures above 2000°C. The 2H close-packed structure may be transformed to the 6H structure by displacing every third layer. The theory of X-ray diffraction from one-dimensionally disordered crystals undergoing the 2H to 6H structural transformation by such a layer displacement mechanism has been developed. The fact that all the observed solid state transformations in SiC crystals commence with the random insertion of stacking faults and then proceed further to create a statistically ordered structure, permits such a theory to be developed. Exact expressions for the diffracted intensity from such crystals have been obtained and the different diffraction effects observable on single crystal X-ray photographs predicted. A comparison of the theoretically predicted diffraction effects with those visible on the X-ray photographs of SiC crystals undergoing the 2H to 6H transformation shows that the structural transformations in SiC occur by the layer displacement mechanism.     

X-ray investigation of the mechanism of phase transformation in single crystals of ZnS,ZnxCd1−xS and ZnxMn1−xS (I). Calculation of diffraction effects by a three parameter model

Hexagonal close-packed (2H) single crystals of ZnS, Zn_xCd_1−xS and Zn_xMn_1−xS are known to undergo solid state transformation to the cubic close-packed (3C) and 6H-structures on annealing at elevated temperatures. The transformations occur by the non-random nucleation of stacking faults on individual close-packed layers parallel to (0001). The nature of the faults involved and their probability distribution during transformation determine the diffraction effects produced along the 10. L reciprocal lattice row by a crystal quenched in an intermediate state of transformation. We have investigated the mechanism of the transformation by comparing the diffraction effects recorded from such crystals on a single crystal diffractometer, with those calculated for an assumed model of the transformation. It is known that in these materials the faults involved in the transformation are deformation faults. To explain the observed diffraction effects we develop a three parameter theoretical model employing a fult probability α for the radom insertion of a deformation fault in the 2H structure, a fault probability β for the deformation faults to occur at three layer separations and a fault probability γ of their occcurrence at 2-layer separations. The probability α corresponds to the development of a fresh nucleus, the probability β to the growth of the 6H nucleus and the probability γ to the growth of a 3C nucleus. This paper develops the necessary theory of X-ray scattering for such a model of the transformation and predicts the diffraction effects for different values of α, β, and γ. The next paper compares these results with experimental observations.     

Keggin型多酸基超分子化合物H3[{H(4-AP)}6(PMoⅤ6MoⅥ6O40)]的结构和电催化性能

通过水热合成方法,以钼酸铵、氯化镍和4-氨基吡啶为原料成功合成了一个Keggin型多酸基超分子化合物H₃[{H(4-AP)}₆(PMo^V₆Mo^VI₆O₄₀)] (4-AP=4-氨基吡啶)。该化合物的结构单元包含一个[PMo^V₆Mo^VI₆O₄₀]^9-阴离子和6个质子化的配体。而[PMo^V₆Mo^VI₆O₄₀]^9-阴离子与配体之间通过N(1)—H(1)…O(3)、N(2)—H(2A)…O(5)和N(2)—H(2B)…O(1)三种氢键相互作用,进而形成二维超分子层。通过X射线单晶衍射、IR和粉末X射线衍射对其进行表征。晶体结构分析表明:该标题化合物属于三方晶系,R-3空间群,a=2.191 2 (10) nm, b=2.191 2 (10) nm, c=1.042 3(5) nm, α=β=90°, γ=120°, V=4.333 8(4) nm³, Z=3, R₁=0.036 2, wR₂=0.095 6, 电催化性质研究表明该标题化合物对H₂O₂和K₂Cr₂O₇具有良好的电催化还原效果,以及对抗坏血酸具有良好的电催化氧化效果。     

An X-ray investigation of growth and deformation faults in a vapour grown 2H SiC crystal

Single crystals of 2H SiC grown by hydrogen reduction of methyltrichlorosilane at 1400°C frequently contain a high concentration of random stacking faults in their hexagonal closepacked | AB | AB | … structure. This given rise to diffuse streaks along reciprocal lattice rows parallel to the c¹ axis for h ? k ≠ 0 mod 3. To investigate the nature of stacking faults in these crystals, the intensity distribution along the 10. l reciprocal lattice row of a 2H SiC crystal was recorded on a 4-circle computer-controlled single crystal diffractometer. The halfwidths of 10. l reflections with l even and l odd were found to be 0.36 and 0.24 reciprocal units respectively. It is observed (i) that the 10. l reflections with l even are highly broadened and (ii) that the halfwidths of l even and l odd reflections are in the ratio of 3 : 2. This suggests that the stacking faults present are predominantly growth and deformation faults. Since the fault concentration is very high, exact theoretical expressions for the halfwidths of 10. l reflections were used to calculate the growth and deformation fault probabilities (α and β) from the observed half widths, without neglecting the second and higher order terms in α and β. It is found that α = 0.11 and β = 0.20. The deformation fault probability (β) is surprisingly high for hard and brittle material like SiC which does not undergo plastic deformation easily. It is suggested that several deformation fault configurations have resulted from a clustering of growth faults.     

Investigation of one‐dimensionally disordered structures of AIIBVI crystals by Monte Carlo technique III. 4H structure with different kinds of stacking faults

To investigate one‐dimensionally disordered (ODD) structures in close packed (cp) crystals, the Monte Carlo computer simulation technique has been applied. Calculations of diffraction intensity distributions along the 10.L reciprocal lattice row from 4H structure with four different kinds of stacking faults (SFs): growth, deformation, layer displacement and extrinsic fault are presented. In particular, using simple frequency function of fault to fault distances, both random and non‐random distributions of SFs are considered. Distinctive features of the diffraction patterns corresponding to the chosen examples of transformations from the parent 4H structure into another small‐period polytypes are discussed in detail.     

基于有机羧酸配体的Co(Ⅲ)/Cu(Ⅱ)配合物的合成、结构及表征

在溶剂热条件下,以含卤素有机羧酸3-溴-吡啶-2,6-二甲酸(H₂L)为配体,以硝酸钴、硝酸铜为金属源,合成了两例配合物:[Co(L′)₃](1)和[Cu(L′)₂]_n(2)(HL′=5-溴-吡啶-2-甲酸),通过元素分析(EA)、X射线单晶衍射(SXRD)、X射线粉末衍射(PXRD)、红外光谱(IR)和热重分析(TGA)进行结构表征。X射线单晶衍射结果表明,配体H₂L在反应过程中发生脱羧现象,生成单羧酸配体5-溴-吡啶-2-甲酸。在配合物1中,每个Co(Ⅲ)都位于略微扭曲的八面体几何构型中,不对称单元中含有两个单核单元,单核单元通过C—H…O氢键形成三维超分子结构。配合物2的不对称单元中含有一个Cu(Ⅱ),两个脱质子的L′^-配体,每个Cu(Ⅱ)都是六配位的,位于扭曲的八面体几何构型中。Cu(Ⅱ)由配体连接生成1D链结构,通过C—H…O氢键形成三维超分子结构。此外,研究了两例配合物的热稳定性能。     

Synthesis,Characterization and Crystal Structure of Ethyl 2-amino-4-(4-fluorophenyl)-6-phenylcyclohexa-1,3-diene-1-carboxylate

Ethyl 2-amino-4-(4-fluorophenyl)-6-phenylcyclohexa-1,3-diene-1-carboxylate was synthesized from ethyl 6-(4-bromophenyl)-4-(4-fluorophenyl)-2-oxocyclohex-3-ene-1-carboxylate and ammonium acetate in glacial acetic acid. The synthesized compound was characterized by elemental analysis, FT-IR, thermogravimetric analysis (TGA), differential thermal analysis (DTA), UV-Visible, and single-crystal X-ray diffraction. The title compound, ethyl 2-amino-4-(4-fluorophenyl)-6-phenylcyclohexa-1,3-diene-1-carboxylate, C₂₁H₂OFNO₂, crystallizes in the orthorhombic space group Pbca with the following unit-cell parameters: a = 17.417(2), b = 9.7287(9), c = 21.014(2) Å, and Z = 8. The crystal structure was solved by direct methods using single-crystal X-ray diffraction data collected at room temperature and refined by full-matrix least-squares procedures to a final R-value of 0.0644 for 1616 observed reflections. An intramolecular N–H…O hydrogen bond generates an S(6) graph-set motif. In the crystal, molecules are linked by N–H…O hydrogen bonds, forming a two-dimensional network.     

Synthesis,Characterization, Crystal Structure,and Thermal Analysis of 4-[(3-acetylphenyl)amino]-2-methylidene-4-oxobutanoic Acid

4-[(3-Acetylphenyl)amino]-2-methylidene-4-oxobutanoic acid (1) is synthesized by a ring opening reaction of itaconic anhydride with 3-aminoacetophenone and characterized by FT-IR, ¹H NMR, UV-Vis, TGA, DTA, and single crystal X-ray diffraction. The crystal of 1 belongs to triclinic unit cell in the P-1 space group with the unit cell dimensions a = 4.9485(3), b = 5.3614(6), c = 22.457(2) Å, α = 88.295(8), β = 89.379(7), γ = 84.495(7), and Z = 2 The crystal structure is solved by direct methods using single-crystal X-ray diffraction data collected at room temperature and refined by full-matrix least-squares procedures to a final R-value of 0.0467 for 1623 observed reflections. Intermolecular N&;sbnd;H?…O and O&;sbnd;H?…O hydrogen bonds links the molecules into chains along [010] direction. In addition the thermal stability of the 1 is determined by using DTA, TGA analysis, and wavelength absorption at λ_max = 297 nm is determined by UV-Vis spectrophotometer.     

Solid-phase synthesis and crystal structure of 5(3-nitrophenyl)-3,7-diphenyl-4H,6H-1,2-diazepine

The title compound, 5-(3-nitrophenyl)-3,7-diphenyl-4H,6H-1,2-diazepine (C₂₃H₁₉N₃O₂), was synthesized, in 76% yield, by one-pot multicomponent solid-phase reaction of 3-nitrobenzylidene phenyl ketone, acetophenone and hydrazine, using the catalyst bismuth nitrate, co-catalyst ZnCl₂, adsorbed on neutral alumina, at 110°C. The compound was characterized by spectral methods and X-ray diffraction studies. The crystals are monoclinic, space group P2₁/c: a = 12.186(2), b = 14.769(3), c = 11.046(2) Å, β = 115.023(3)°, Z = 4; R = 0.0418 for 2576 observed reflections. The diazepine ring assumes a twist chair conformation. The dihedral angles between the mean planes through the diazepine ring and the nitrophenyl rings and two phenyl are: 89.19(5)°, 45.85(5)° and 20.80(6)°, respectively. The crystal structure is stabilized by C-H…N, C-H…O, C-H…π hydrogen bonds and π-π-stacking interactions.     

A model for the growth of anomalous polytype structures in vapour grown SiC

A number of polytype structures observed in vapour grown SiC crystals have a unit-cell which is an integral multiple of the unit-cell of the basic 6H, 15R or 4H structure. The growth of such anomalous structures cannot be understood in terms of spiral growth round a single screw dislocation in a basic matrix. However many of these polytype crystals display a single growth spiral on their (0001) face indicating that they have resulted from spiral growth round a single screw dislocation. It is shown that this anomaly can be resolved if the basic matrix is assumed to contain stacking faults near the surface at the time of the origin of the screw dislocation ledge. This possibility, overlooked in the earlier deduction of polytype structures, must be taken into consideration since vapour grown SiC crystals frequently contain a high concentration of random stacking faults, producing continuous streaks on their X-ray diffraction photographs. The most probable fault configurations that can occur in 6H, 15R and 4H structures of SiC have been deduced from a calculation of their stacking fault energy. These fault configurations are then considered to lie at different distances from the surface at the time of the origin of a screw dislocation ledge. Such a faulted ledge gives rise to polytype structures during subsequent spiral growth even if the screw dislocation has an integral Burgers vector. The most probable series of polytype structures that can result from such a faulted matrix model are deduced. It is shown that nearly all the polytype structures of SiC hitherto regarded as anomalous (such as 36H, 54H, 66H, 45R, 90R etc.) are among the expected structures and there is no need to postulate a complicated configuration of cooperating dislocations to account for their growth.     

Hirshfeld Surface Analysis and Crystal Structure of [2-Bromo-4-(4-Fluoro-Benzoyl)-Phenoxy]-Acetic Acid Ethyl Ester

The title compound C₁₇H₁₄BrFO₄ was synthesized using 3-Bromo-4-hydroxy-phenyl-(4-fluoro-phenyl)-methanone, ethyl chloroacetate, and anhydrous potassium carbonate. Its structure was established using elemental analysis, NMR, and single crystal X-ray diffraction techniques. The compound crystallizes in orthorhombic crystal system and space group Pbca. The cell parameters are a = 10.1444(13) Å, b = 8.2781(10) Å, c = 38.423(5) Å, Z = 8, V = 3226.6(7) ų. The dihedral angle between two least squares planes of two phenyl rings bridged by keto carbonyl group is ?28.2(5)°. The molecule exhibits intermolecular interactions of the type C?H…F and C?H…O. The intercontacts in the crystal structure are studied using Hirshfeld surface analysis.     

Modelling diffraction patterns from one‐dimensionally disordered structures of AIIBVI crystals by Monte Carlo Technique IV. The 6H structure with different kinds of stacking faults

To investigate the one‐dimensionally disordered structures (ODDS) in the close packed (cp) crystals, the Monte Carlo computer simulation technique has been applied. Calculations of the diffraction intensity distributions along the 10.L reciprocal lattice row from the 6H(33) structure with the four different kinds of the stacking faults (SFs): growth, deformation, layer displacement and extrinsic fault are presented. In particular, using the simple frequency functions of the fault to fault distances, both random and non‐random distributions of the SFs are considered. Distinctive features of the diffraction patterns corresponding to the chosen examples of the transformations from the parent 6H(33) structure into another small‐period polytypes are discussed in detail. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mesophase-Preceding Crystal Packing of 4,4'-Dialkyl-Substituted Salicylideneanilines; C10H21O–C6H3(OH)–CH=N–C6H4–С7Н13) Structure

Crystallography Reports - The crystal structure of 4,4'-substituted salicylideneaniline C10H21O–C6H3(OH)–CH=N–C6H4–C7H13 has been investigated by X-ray diffraction. A...     

1,3,5-三(羧基甲氧基)苯镍配位聚合物的合成、晶体结构及性质研究

采用溶剂热法,1,3,5-三(羧基甲氧基)苯为定向配体和乙酸镍反应构筑了一个新型的金属配位聚合物[Ni(TB)₂(H₂O)₂]_n·2H₂O,其中H₃TB=1,3,5-三(羧基甲氧基)苯,通过元素分析、IR及X射线单晶衍射对配合物结构进行表征,并研究其荧光性质、热稳定性及Hirshfeld表面作用力。单晶结构分析表明,该配合物属于三斜晶系,空间群$P \overline{1}$,配合物中心离子Ni(Ⅱ)分别与来自两个水分子上的氧原子及四个不同1,3,5-三(羧基甲氧基)苯配体的羧酸氧原子配位,形成六配位的NiO₆八面体构型,并通过与1,3,5-三(羧基甲氧基)苯配体的氧原子配位不断延伸形成具有孔洞结构的一维链状构型。配合物具有良好的荧光性能和热稳定性。Hirshfeld表面作用分析表明配合物分子中O…H/H…O作用占主导且占比为39.0%,而H…H的作用力占比为25.9%,O…O的作用力占比为13.6%。     

TEM-Untersuchungen von Gitterfehlern in ZnSiP2-Einkristallen

Results are dealt with concerning TEM investigations of lattice defects in ZnSiP₂ single crystals. After the crystal growth dislocations or stacking faults were found in a few cases only. More frequently twins were present in the microstructure. The crystallographic elements of twinning are {112} 〈111〉. After plastic deformation by bending at 900 °C local dislocation arrangements with high defect density (N_v ≈ 10⁶…︁ 10⁷ cm⁻²) were observed. By means of the diffraction contrast one Burgers vector b = 1/2 〈111〉 could be identified. In some cases the crystals also contained wide deformation stacking faults, which were limited by partial dislocations. The density of twins was not increased under the conditions of deformation reported here. As it can be concluded from investigations of Oettel et al. and from the results of the twin analysis, slip and generation of stacking faults take place on {112}-planes in ZnSiP₂ crystals. Crystallographic considerations on both processes are dealt with.     

The structure,perfection and annealing behaviour of SiC needles grown by a VLS mechanism

Over 50 different single crystals of SiC, grown by a vapour-liquid-solid mechanism, have been examined by optical and X-ray diffraction methods to determine their structure, perfection and annealing behaviour. All the crystals studied had either the hexagonal close-packed 2H (ABAB…) structure or the cubic close-packed 3C (ABCABC…) structure or a combination of both, and invariably contained a random distribution of stacking faults on their basal planes. The thermal stability of the structures was studied by annealing them between 1300–2200 °C in an inert argon atmosphere, and reexamining the structure of the crystals after each annealing run. Structural transformations were found to commence in different crystals at different temperatures between 1400 and 1800 °C. The transformations were found to be irreversible, not martensitic and appear to involve the nucleation of the new phase by the insertion of stacking faults followed by its growth during the annealing. The mechanism of the solid-state transformations, the influence of faults and impurities, and the thermal stability of different SiC structures are discussed.     

Investigation of One‐Dimensionally Disordered Structures of AIIBVI Crystals by Monte Carlo Technique. II. 2H Structure with Different Kinds of Stacking Faults

To investigate 2H disordered structures in A^IIB^VI compounds, the Monte Carlo computer simulation technique has been applied. Calculations of diffraction intensity distributions along the 10.L reciprocal lattice row from 2H structure with four different kinds of stacking faults (SFs) are presented. In particular, both random and non‐random distributions of SFs are considered. The chosen examples of transformations from the parent 2H structure into another small‐period polytypes due to simple frequency function of fault to fault distances are discussed in detail.     

Crystal structure of 17α‐acetoxyprogesterone,C23H32O4

The crystal structure of the title compound (C₂₃H₃₂O₄) has been determined by X‐ray diffraction methods. It crystallizes in the orthorhombic space group P2₁2₁2₁ with cell parameters: a = 10.86(1), b = 11.95(2), c = 15.65(5) Å and Z = 4. The structure has been refined to an R‐value of 0.045 for 1610 observed reflections. Ring A exists in sofa conformation, Ring B adopts a distorted chair conformation while as Ring C assumes a chair conformation. The five membered ring D adopts a half‐chair conformation. The crystal structure is stabilized by intra‐ and intermolecular C‐H…O interactions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of Crystalline Polymeric Solids at Reduced Beam Damage in the High Voltage Electron Microscope

A special technique was used for investigating polymers in the electron microscope at essentially reduced radiation damage. The method is based on a high voltage electron microscope (accelerating voltage of 1 MV) and the use of highly sensitive X-ray films. Compared with the conventional transmission electron microscopy this technique reduces the specimen damage by a factor of 50 … 100. Diffraction contrast can therefore be used to investigate the structure of semi-crystalline polymers. Using samples of polyethylene, the arrangement of the lamellae was determined by bright field and dark field images and diffraction patterns. There are further advantages concerning the improved possibility of investigating very thick specimens (thicknesses above 5 μm). Thus, a better stereoscopic analysis of extended structures is possible, and in-situ deformation tests of polymers can be performed in the electron microscope.     

[Co(H2O)6](C18H15O4SO3)2·4H2O的合成和晶体结构

以芒柄花素为先导化合物,合成了水溶性的[Co(H2O)6](C18H15O4SO3)2·4H2O,并采用IR, 1H NMR, TG-DTA, XRD和单晶X射线衍射法对其结构进行了表征.单晶X射线衍射结果表明:[Co(H2O)6]2+、C18H15O4SO 3和H2O之间存在多种氢键,形成晶体结构中的亲水区.异黄酮骨架间反平行排列,面对面和边对面芳香堆积作用同时存在于其中,构成晶体结构中的疏水区.磺酸根是连接亲水区和疏水区的桥梁.氢键、芳香堆积作用以及阴阳离子之间的静电引力共同将标题化合物组装成具有三维网络结构的超分子.