摘要:

AbstractWe report on a special technique for high‐temperature solution growth (flux‐), which can be used to grow compounds which have only a small solubility in the flux or only exist in a small existence range (concerning temperature and concentration). By two crucibles placed into one another, an inner growth region will be separated from an outer solution region. The regions are connected by holes in the inner crucible. By this method BaSO4crystals of high quality are grown from NaNO3flux and LiCl–KCl flux. Growth experiments using this method were done with the incongruently melting high‐temperature superconductor YBa2

ISSN:0232-1300    

DOI:10.1002/crat.2170300109

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractSingle crystals of corundum were grown by the top‐seeded solution growth technique from a cryolite, Na3AlF6, solvent. The relationship between the growth rate (mg/h) of a crystal and the temperature difference (= supersaturation) or the rotation rate of a seed crystal was investigated, and optimum growth conditions for obtaining single crystals with good quality are discusse

ISSN:0232-1300    

DOI:10.1002/crat.2170300110

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA systematic defect characterization by X‐ray diffraction was carried out on crystalline KCl system with Cd++impurities at various levels, viz. 2, 4, 6, 8, and 10 mole%. Quantitative estimation of the amount and nature of defects was done from the integrated X‐ray intensity measurements of the samples. Further analyses of the experimental data indicate enhancement of the Debye‐Waller factor with concentration of Cd++impurities. The measured density and the cell constant values at room temperature yield vacancy estimations for the system. The observed change of Bravais lattice of the system for Cd++concentrations from 4 mole% with appreciable enhancement of intensity of Bragg reflections of mixed indices are reported and disc

ISSN:0232-1300    

DOI:10.1002/crat.2170300111

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractComparison of phases observed in air at 900–980°C in the Ln–Ba–Cu–O (Ln = Lanthanoid) systems is reported. On the basis of the occurrence of compounds found in these Ln2O3–BaCO3–CuO systems they must be divided into at least three subgroups: the first is characteristic of La, Pr and Nd, the second specific for Sm and Eu, and the third common to the smaller lanthanoids, the Y‐type elements, with some variation wit

ISSN:0232-1300    

DOI:10.1002/crat.2170300112

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractCreation of enantiomorphous forms in sodium chlorate and enantiomorphous nature of surface micromorphology were studied by optical microscopy. It was shown that when the small number of crystals nucleates spontaneously in unstirred, unseeded solutions then exclusively left‐ (L) or right‐handed (D) crystals can be formed. At the large number of nucleated crystals the probability of the creation of L and D form is nearly the same. L and D crystals can be distinguished by the shape of growth or dissolution cent

ISSN:0232-1300    

DOI:10.1002/crat.2170300113

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe crystal structure of methyl‐16, nor‐5‐hydroxy‐6,7,15‐trioxo dehydroabietate has been determined from three‐dimensional X‐ray diffraction data. The compound crystallizes in the orthorhombic space group P21212 with unit cell parametersa= 19.226(3) Å,b= 11.075(3) Å,c= 8.375(2) Å,Z= 4,V= 1783.3(7) Å3,d0= 1.36 gcm−3. The gross structure was determined by direct methods which on refinement yielded a final value ofRindex as 0.038. Ring A is a chair, ring B an envelope whereas the ring C adopts a strictly planar conformation. The rings A and B aretransfused. The ester group at C4 iscisfused to methyl carbon C15 whereas another methyl carbon C18 andoxoO(15) of the isopropyl group at C13 are rotated to positions 0.107(3) Å and 0.179(2) Å out o

ISSN:0232-1300    

DOI:10.1002/crat.2170300114

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractFive salts of KNO3.xNH4NO3with differentxvalues have been synthesized and their structures have been solved and refined.Xvalues obtained from refined fractional occupation number of K atom are in accord withxobtained from chemical analysis. The linear dependence of volume cell on obtainedxhas been given.

ISSN:0232-1300    

DOI:10.1002/crat.2170300115

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe enantiomeric [(S)‐(–)‐MBP3B] and the racemic form [(±)‐MBP3B]of the title compound with the formula C3H5O–C6H4–CO2–C6H4–OC5H11were studied by single crystal analysis at room temperature.(S)‐(–)‐MBP3B crystallizes in the orthorhombic space group P212121witha= 7.835(3) Å,b= 11.093(6) Å,c= 44.820(3) Å and 8 molecules per unit cell. The structure was determined from 966 reflections with intensities>3σ. The refinement with isotropic temperature factors leads toR= 0.094.The crystals of the racemic form are monoclinic, space group P21/a witha= 7.899(5) Å,b= 11.046(6) Å,c= 22.845(12) Å, β = 99.28(3)°,Z= 4.1236 diffractometer data (I>3σ) were refined by least‐squares methods with anisotropic temperature factors for the non‐H atoms toR= 0.070.The packing arrangement for both forms shows a layer‐like structure with very similar packing coefficients,k= 0.7085 for the pure enanti

ISSN:0232-1300    

DOI:10.1002/crat.2170300116

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractTlInSe2and TlInTe2crystallize in a tetragonal cell (space group14/mcm) (MÜLLER et al.). A primitive cell of these ternary crystals contains two formula units. All the Tl atoms in these compounds are univalent. The In atoms are trivalent being in a tetrahedral environment consisting of Se or Te atoms. InSe4or InTe4fragments of a unit cell form the chains extended alongc‐axis coinciding with [001] directions. Such chains are bonded to each other by Tl atoms.TlGaSe2and TlInS2crystals belong to the monoclinic system (space groupC2/c) (MÜLLER, HAHN; WONG‐NG et al.). The primitive cell of these crystals contains eight formula units. The lattice of TlGaSe2crystals consists of strictly periodic two‐dimensional layers arranged parallel to the (001) plane. Each successive layer is turned through a right angle with respect to the previous one. The fundamental structural unit of a layer is the Ga4Se10polyhedron representing a combination of four elementary GaSe4tetrahedra linked together by bridging Se atoms. The Tl atoms are in trigonal prismatic voids resulting from the combination of the Ga4Se10polyhedra into a layer. The Tl atoms form nearly planar chains along the [110] and [110]dir

ISSN:0232-1300    

DOI:10.1002/crat.2170300117

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing a total of 1052 Bragg reflections of silicon, an X‐ray investigation has been carried out to deduce the anharmonic thermal parameter β, apart from the estimation of the harmonic contribution of the thermal vibration at room temperature. Reflections of typeh+k+l= 4n, and 4n± 1 were used to estimate these parameters using MoK α radiation and a Nonius CAD‐4 X‐ray diffractometer. We obtainBsi, = 0.451(0.008) Å2and βsi= 0.279(2.630) eV Å−3withR= 3.12%. The presentBand β values are in very good agreement with the e

ISSN:0232-1300    

DOI:10.1002/crat.2170300118

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY