共查询到20条相似文献,搜索用时 250 毫秒
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采用顶部籽晶法,以NaF为助熔剂生长非线性光学晶体材料β-BaB2O4(简称BBO)晶体.在生长过程中发现挥发物掉落在晶体表面并严重腐蚀晶体.通过X射线粉末衍射分析,发现挥发物的主要成分是NaF,它不仅腐蚀晶体表面,而且引起晶体内部包裹物的形成.X射线衍射分析和质谱分析表明包裹物的主要成分是BaB2O4,另有少量Na+存在.探讨了由挥发物引起晶体内部形成包裹物的机理. 相似文献
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Rachid Essehli Brahim El Bali Mohammed Lachkar Michael Dusek Fejfarova Karla Michael Bolte 《Journal of chemical crystallography》2006,36(10):655-660
(C2N2H10)2Mg(HP2O7)2·2H2O, is a new inorganic organic hybrid structure. It has been synthetized using wet chemistry. Its crystal structure consists of cis- and trans-edge sharing [MgO4(H2O)2] octahedra resulting in chains, which are linked via [HP2O7] units to form [Mg(HP2O7)2(H2O)2]4− layers. The Mg2+ cations and the ethylendiammonium cations are located on centers of inversion. The ethylendiammonium cations are alternately located in the interlayer space. The cohesion of the crystal is well ensured by coulombic interactions between anions and cations and by several hydrogen bonds. The diphosphate anion shows an eclipsed conformation. 相似文献
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S. I. Troyanov A. V. Kostrikin F. M. Spiridonov B. E. Zaĭtsev S. V. Tarasova O. V. Kosenkova 《Crystallography Reports》2006,51(3):414-418
Single crystals of Rb2[GeO2(OH)2] · 2H2O are studied by X-ray diffraction. The crystals belong to the orthorhombic system, sp. gr. Pna21, a = 13.523(6) Å, b = 8.143(4) Å, c = 13.407(6) Å, Z = 8, R 1 = 0.0506. In [GeO2(OH)2]2? anions, the Ge-O distances (1.71–1.73(1) Å) are shorter than the Ge-OH distances (1.76–1.80(1) Å). Anions are linked to each other by pairs of hydrogen bonds to form infinite chains. The chains are linked by hydrogen bonds involving water molecules to form a 3D structure. The assignment of the bands in the IR spectrum of the compound under study is performed. 相似文献
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The optical unpolarized absorption spectra of Hg2Cl2 and Hg2Br2 single crystals were measured in the spectral range 230–400 nm. A sharp exciton peak and other absorption bands of both halides were observed near the fundamental absorption edge. The absorption peaks due to the splitting of the halogen doublet were also observed. Positions of the exciton peaks are characteristic for the Frenkel (localized) type of excitons. Possible interpretations of the other observed bands are discussed. 相似文献
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S. Haussühl 《Crystal Research and Technology》1994,29(1):119-124
Single crystals of the title compounds having optical quality and dimensions of several cm were grown from aqueous solutions. The elastic and thermoelastic constants were determined from ultrasonic resonance frequencies of thick plates. The true point symmetry of K2S2O6 and Rb2S2O6, which is screened by a hexagonal hypermorphy, could be clearly revealed to be trigonal (32) by the existence of the elastic constant c14. In the case of CaS2O6 · 4H2O and SrS2O6 · 4H2O the constant c14 of the specimens appeared too small to confirm the trigonal symmetry group required from electrooptic and non-linear optic effects unambiguously. The isotypy of K2S2O2 and Rb2S2O6 as well as that of CaS2O6 · 4H2O and SrS2O6 · 4H2O is confirmed by their elastic behaviour. The mean elastic stiffness of dithionates is closely related to that of the corresponding sulphates. In the vicinity of the second-order phase transition of K2S2O6 near 235 K weak anomalies of the temperature derivatives of the longitudinal elastic stiffnesses are observed. 相似文献
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Refractive indices and their dispersion in the wavelength range from 365 nm to 2325 nm and transmission ranges of the tetragonal melilite‐type germanates Sr2MgGe2O7, Sr2ZnGe2O7 and Ba2ZnGe2O7 were determined. The uniaxial positive crystals Sr2MgGe2O7 and Ba2ZnGe2O7 both offer the possibility for phase matched second harmonic generation, a detailed analysis of phase matching conditions is given. The refractive indices of Sr2ZnGe2O7 show an isoindex (isotropic) point at 467 nm. The investigation was performed on Czochralski grown large single crystals. The crystal structure of all three germanates were determined by means of X ‐ray diffraction. The results corroborate unmodulated melilite‐type structures at room temperature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Jamal Bennazha Fatima Erragh Ali Boukhari Elizabeth M. Holt 《Journal of chemical crystallography》2000,30(11):705-716
Syntheses and single-crystal X-ray structural results are reported for three new mixed diphosphates of the family AI
2BII
3(P2O7)2; Ag2Co3(P2O7)2 (I), Ag2Mn3(P2O7)2 (II), and Na2Cd3(P2O7)2 (III). All crystallize in the triclinic system, space group P1 bar: (I) a = 5.351(4), b = 6.375(4), c = 16.532(4) Å, = 80.83(6) = 81.45(4), = 72.87(5)°, V = 528.9(6) Å3, Z = 2, D
calc = 4.649 mg/m3, R/Rw = 0.0428/0.0548 for 3949 obs. reflns; (II) a = 5.432(7), b = 6.619(6), c = 16.51(3) Å, = 80.78(8) = 82.43(9), = 72.82(7)°, V = 557.7(13) Å3, Z = 2, D
calc = 4.338 mg/m3, R/Rw = 0.0679/0.1303 for 2100 obs. reflns and (III) a = 5.67(3), b = 7.08(4), c = 7.90(4) Å, = 77.0(2), = 82.5(2), = 67.8(2)°, V = 286(3) Å3, Z = 2, D
calc = 4.249 mg/m3, R/Rw = 0.0307/0.0342 for 1945 obs. reflns. (I) and (II) are isostructural but (III) is of a different type. All three structures are characterized by layers of P2O7 groups alternating with layers of mixed metal atoms. Differences are seen in the conglomerate bonding patterns of B atoms and in the irregular geometry of Ag in (I) and (II) compared to the octahedral bonding seen for Na in (III). The differences in structure may be understood in terms of the ratios of the ionic radii of A and B atoms. 相似文献
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Z. Elaoud S. Kamoun T. Mhiri A. Daoud A. Driss 《Journal of chemical crystallography》2004,34(5):337-341
The salt bis 4-benzyl piperidinium monohydrogenmonophosphate pentahydrate is orthorhombic with the following unit cell dimensions: a = 11.235(2) Å, b = 27.924(6) Å, c = 9.321(4) Å space group Pca21 with Z = 4. The structure was solved by the Patterson method and refined to final R value of 0.049 for 1802 independent reflections. The flack parameter is 0.14 with an e.s.d. of 0.23. The structure consists of infinite parallel two-dimensional [110] planes built of mutually connected ions and water molecules by strong O—H,...,O and N—H,...,O hydrogen bonding. There are no contacts other than normal van der Waals interactions between the layers. 相似文献
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G. Amirthaganesan M. A. Kandhaswamy V. Srinivasan 《Crystal Research and Technology》2005,40(3):212-216
Single crystals of a new compound, (NH4)2CuBr2Cl2.2H2O, were grown from saturated aqueous solution at room temperature by slow evaporation method. The grown crystals were characterized through elemental, powder XRD, thermal and DSC analyses and FTIR and far IR spectra. The elemental analysis and the decomposition pattern formulated using the TG‐DTG studies confirm the stoichiometry of the compound. The crystallinity of the compound is confirmed from the powder XRD pattern. A preliminary single crystal X‐ray diffraction structural analysis reveals that the title compound belongs to the orthorhombic system with a = 7.7466 Å, b = 7.783 Å and c = 8.1211 Å. The low temperature DSC shows thermal anomalies at –161.1, –156.5, –152.4, –145.2, –134, –18.5, and 1.4°C during the heating run and at –4.3, –54.8, –66.1, –90.6, –109.7 and –147.2 °C during the cooling run. The thermal hysterses indicate first order phase transitions in the title compound at these temperatures. The FTIR spectra were used to assign the characteristic vibrational frequencies due to NH4+, CuX42– ions and other chemical bonds. The effect of substitution of two bromine atoms on the phase transitions of a closely related crystal, diammonium tetrachloro cuprate dihydrate is also discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Optical transmittance and reflectance spectra of MnIn2S2Se2 single crystals are measured in the wavelength range from 0.5 to 30 μm. The interference method is used to determine the refractive index of the compound for wavelengths between 0.8 and 12 μm. From an analysis of the absorption spectrum it follows that the fundamental edge is due to forbidden indirect transitions between parabolic bands for the polarization E ⊥ c with a gap energy of 1.50 eV at room temperature. 相似文献
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Polycrystalline samples in the ternary system La2Mo2O9-Sm2W2O9-Sm2Mo2O 9 + were synthesized in air. The region of the existence of compounds with the lanthanum molybdate (La2Mo2O9) structure in this system was determined. The polymorphism of the synthesized compounds was studied. Doping with samarium or with samarium and tungsten was shown to lead to the suppression of the transition between the monoclinic and cubic phases α → β and the appearance of the transition β ms → β between two cubic phases. In samples with a high samarium content, the phase transition β ms → β manifests itself as significant anomalies in the temperature dependences of the dielectric permeability and electric conductivity. An increase in the concentration of samarium in the samples leads to a substantial decrease in the conductivity compared with the nondoped compound La2Mo2O9. 相似文献