The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as‐grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30 °C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH4)2C2O4 · H2O molecules are in excellent agreement with the low‐index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph. 相似文献
Two new malonate-containing uranyl complexes with carbamide of the formulas [UO2(C3H2O4)(Urea)2] (I) and [UO2(C3H2O4)(Urea)3] (II), where Urea is carbamide, and one uranyl oxalate complex of the formula [UO2(C2O4)(Urea)3] (III) were synthesized, and their crystals were studied by X-ray diffraction. The main structural units in crystals I are the electroneutral chains [UO2(C3H2O4)(Urea)2]∞ belonging to the crystal-chemical group AT11M21 (A = UO22+, T11 = C3H2O42-, M1 = Urea) of uranyl complexes. Crystals II and III are composed of the molecular complexes [UO2(L)(Urea)3], where L = C3H2O42- or C2O42-, belonging to the crystal-chemical group AB01M31 (A = UO22+, B01 = C3H2O42- or C2O42-, M1 = Urea). The characteristic features of the packing of the uranium-containing complexes are discussed in terms of molecular Voronoi–Dirichlet polyhedra. The effect of the Urea: U ratio on the structure of uranium-containing structural units is considered. 相似文献
The crystal and molecular structure of 1-Ethyl-3[tris(trimethylsiloxyl)silyl]pyrrolinium hydro-chloride (C15H38N+O3Si4 · C1−) has been determined by direct methods. The title compound crystallizes in the monoclinic space group C2/c with a = 20.640(3), b = 19.494(2), c = 27.34(3) Å, β = 90.60(4)°, V = 11000(13) Å3, Z = 16, Dx = 1.034 Mg m−3. There are two molecules with different conformations in the crystal. The pyrroline rings are non-planar.-The Si O Si angles range from 149(1)° to 163(1)°. Two of the SiMe3 groups are disordered. All molecules are connected by C1− – N+ contacts and C1− - HN+ hydrogen bonds to form double chains. 相似文献
The paper deals with the solubility of (YSmLuCa)3 (FeGe)5O12 garnet in PbO—B2O3 flux. An anionic model explaining the effect of B2O3 on the solubility of rare earth garnet is suggested. This model is based on the assumption that PbO in the melted mixture of PbO, B2O3, Fe2O3, R2O3, CaO, GeO2 dissociates into Pb2+ and O2−. The oxygen anions react with the other oxides under the formation of BO33−, FeO33−, RO69−, CaO22− and GeO32− anions, until the equilibrium is established. The garnet is dissociated into the anions mentioned above. The validity of the model is verified by an agreement of the experimentally determined saturation temperatures of the melts for LPE of garnet layers with the Arrhenius-type expression of the solubility product of garnet where xi denotes the equilibrium concentrations of the anions in the melt and x° is the Ge content of the garnet film. 相似文献
The experimental results of the effect of concentration of Mn(II) ions on the growth kinetics of different faces of ammonium oxalate monohydrate single crystals from aqueous solutions at a constant temperature and different predefined supersaturations are described and discussed. It was observed that: (1) at a given supersaturation σ, Mn(II) ions lead to a decrease in the growth rates of different faces of AO crystals, (2) the growth of a particular face of the crystals occurs above a critical supersaturation σd but there is also another supersaturation barrier σ* when the rate abruptly increases with σ, (3) the values of σd and σ* increase with increasing concentration of the impurity, and (4) the values of σd depend on the growth kinetics of a face but those of σ* are independent of face growth kinetics. The experimental R(σ) data for different Mn(II) concentrations ci were analysed according to the model involving complex source of cooperating screw dislocations and concepts of instantaneous and time‐dependent impurity adsorption. It was found that: (1) for a given face the differential heat of adsorption Qdiff is higher during instantaneous impurity adsorption than that during time‐dependent adsorption, and (2) the values of Qdiff involved during instantaneous adsorption are related with face growth kinetics but those during time‐dependent adsorption are independent of face growth kinetics. 相似文献
The synthesis and X-ray diffraction analysis of K2(H5O2)[UO2(C2O4)2(HSeO3)] single crystals have been performed. This compound crystallizes in the triclinic system with the unit-cell parameters a = 6.7665(4) ?, b = 8.8850(4) ?, c = 12.3147(7) ?, α = 94.73°, β = 90.16°, γ = 92.11°, sp. gr. P[`1]P\bar 1, Z = 2, and R = 0.019. The basic structural units are island [UO2(C2O4)2(HSeO3)]3− groups, which belong to the AB201M1 crystallochemical group of uranyl complexes (A = UO22+, B01 = C2O42−, and M1 = HSeO3−). Uraniumcontaining complexes are linked through K+ and H5O2+ ions and via a system of hydrogen bonds with the participation of oxonium hydrogen atoms in this structure. 相似文献
The results of experimental studies of the electrophysical and magnetic properties of solid solutions based on the AB compounds with anion (Zn3(PxAs1−x)2 and cation (ZnxCd1−x)3 P2 substitution are reported. The Zn3(AsxP1−x)2 solid solutions are characterized by p-type conductivity (∼ 1015 1017 cm−3), low Hall mobility and conductivity of ∼ 10−2 — 10−3 ohm−1 cm−1. In the (ZnxCd1−x)3P2 solid solutions the samples rich in zinc are p-type, those rich in cadmium — n-type, the carrier concentration is ∼ 1016 — 1018 cm−3. From the measurements of the magnetic properties of the above mentioned alloys it is shown that in the investigated solid solutions a transition from the structure with direct optical transition to those with indirect optical transition occurs. 相似文献
Compounds K2[UO2(C3H2O4)2] · H2O (I) and Rb2[UO2(C3H2O4)2] · H2O (II) are synthesized and their crystal structures are determined by X-ray diffraction. The compounds crystallize in the monoclinic
crystal system; for I, a = 7.1700(2) ?, b =12.3061(3) ?, c = 14.3080(4) ?, β = 95.831(2)°, space group P21/n, Z = 4, and R = 0.0275; for II, a = 7.1197(2) ?, b = 12.6433(4) ?, c = 14.6729(6) ?, β = 96.353(2)°, space group P21/n, Z = 4, and R = 0.0328. It is found that I and II are isostructural. The main structural units of the crystals are the [UO2(C3H2O4)2]2− chains, which belong to the AT11B01 (A = UO22+, T11, and B01 = C3H2O42−) crystal chemical group of uranyl complexes. The chains and alkali metal ions R (R = K or Rb) are connected by electrostatic interactions and hydrogen bonds. Some specific structural features of [UO2(C3H2O4)2]2− complex groups are discussed. 相似文献
First-principles calculations of the geometry and electronic structure of the impurity center in SrTi1 − xMnxO3 have been performed. Neutral and negatively charged defects are considered. It is found that the doubly charged impurity
center is polar; it has C4v symmetry and electronic state 4B1 with electron polaron localized at one of the neighboring titanium atoms. It is shown that this state is due to the spontaneous
breaking of the defect local symmetry: Oh(4A1g) → D4h(4B1g) → C4ν(4B1). 相似文献
Three heteroacidoligand uranyl complexes M4[(UO2)2C2O4(SO4)2(NCS)2] (M = K+ (I), Rb+ (II)) and K4[(UO2)2C2O4(SeO4)2(NCS)2] (III) have been synthesized and their crystal structure has been determined by X-ray diffraction analysis. The compounds I–III are isostructural and crystallized in the monoclinic system, sp. gr. P21/c, Z = 2, a = 11.5548(3) ?, b = 7.0847(1) ?, c = 13.5172(3) ?, β = 93.130(1)°, V = 1104.90(4), R = 0.015 (I); a = 11.5854(9) ?, b = 7.3841(6) ?, c = 13.9072(9) ?, β = 95.754(3)°, V = 1183.74(15), R = 0.0235 (II); a = 11.6715(3) ?, b = 7.1418(2) ?, c = 13.8546(1) ?, β = 93.539(1)°, V = 1152.66(5), R = 0.0126 (III). Basic structural units of these crystals are [(UO2)2C2O4(XO4)2(NCS)2]4− chains, which belong to the crystallochemical group A2K02B22M21 (A = UO22+, K02 = C2O2−4, B2 = SO42− or SeO42−, M1 = NCS−) of uranyl complexes. Uranium-containing chains are connected into a 3D framework via a system of electrostatic interactions
with potassium or rubidium cations from outer spheres.
Original Russian Text ? I.V. Medrish, E.V. Peresypkina, A.V. Virovets, L.B. Serezhkina, 2008, published in Kristallografiya,
2008, Vol. 53, No. 3, pp. 495–498. 相似文献
Single crystals of the compound K8[(UO2)2(C2O4)2(SeO4)4] · 2H2O (I) are synthesized, and their structure is investigated using X-ray diffraction. Compound I crystallizes in the monoclinic system with the unit cell parameters a = 14.9290(4) ?, b = 7.2800(2) ?, c = 15.3165(4) ?, β = 109.188(1)°, V = 1572.17(7) ?3, space group P21/n, Z = 2, and R = 0.0297. The uranium-containing structural units of crystals I are dimers of the composition [(UO 2)2(C2O4)2(SeO4)4]8−, which belong to the crystal-chemical group AB01B2M1 (A = UO22+, B01 = C2O42−, B2 = SeO42−, M1 = SeO42−) of the uranyl complexes. The [(UO2)2(C2O4)2(SeO4)4]8− dimers are joined into a three-dimensional framework through electrostatic interactions with the outer-sphere potassium cations.
Original Russian Text ? L.B. Serezhkina, E.V. Peresypkina, A.V. Virovets, A.G. Verevkin, D.V. Pushkin, 2009, published in
Kristallografiya, 2009, Vol. 54, No. 1, pp. 68–71. 相似文献
The effect of excess W and La3+, Y3+, and Mo6+ impurities on the luminescence spectra and the thermally stimulated luminescence of PbWO4 crystals is studied. A high tungsten content (up to 1 at %) in the charge mixture results in a high luminescence intensity in the green spectral region. Lanthanum impurity decreases the transmission in the short-wavelength (k > 29 000 cm?1) spectral region. Lanthanum and yttrium impurities decrease the luminescence intensity. At low (102 ppm) concentrations, Mo impurity can somewhat increase the light yield. However, the presence of Mo in PbWO4 shifts the absorption-band edge to longer wavelengths, while an increase in the Mo concentration above 102 ppm decreases the luminescence intensity. 相似文献
The single-crystal X-ray diffraction analysis of K2[Co(H2O)6](C8H5O4)4 ? 4H2O has been carried out. The K2[Co(H2O)6](C8H5O4)4 ? 4H2O single crystals are obtained in attempting to grow the KAP crystals with the maximum possible content of Co2+ impurity cations. The crystals are isostructural to the earlier-studied similar crystals with Ni(II). The structure is formed by double layers of biphthalate anions and the Co2+ and K+ cations in between. The Co2+ cations are coordinated only by water molecules, whereas the coordination of the K+ cations involves both the biphthalate anions and water molecules. A detailed crystal chemical analysis, together with the data on the growth kinetics of KAP crystals in the presence of Co2+ and the mass-spectrometric data obtained earlier for the KAP crystals, leads to the conclusion that the Co2+ impurity cations should be located in the form of the [Co(H2O)6]2+ cationic complexes in the interblock layers of the KAP crystals. 相似文献
Single crystals of the compound {NH2(C2H5)2}2[(UO2)2C2O4(CH3COO)4] · 2H2O (I) are synthesized, and their structure is investigated using X-ray diffraction. Compound I crystallizes in the monoclinic system with the unit cell parameters a = 9.210(2) ?, b = 14.321(3) ?, c = 12.659(3) ?, β = 105.465(13)°, V = 1609.2(6) ?3, space group P21/c, Z = 2, and R = 0.0198. The structural units of crystals I are binuclear groups of the composition [(UO2)2C2O4(CH3COO)4]2− with an island structure, which belong to the crystal-chemical group A2K02B401 (A = UO22+, K02 = C2O42−, B01 = CH3COO−) of the uranyl complexes, diethylammonium cations, and water molecules. The uranium-containing groups are joined into a three-dimensional
framework through electrostatic interactions with diethylammonium cations and a system of hydrogen bonds, which are formed
with the participation of the atoms involved in the composition of the water molecules, oxalate ions, acetate ions, and diethylammonium
cations.
Original Russian Text ? L.B. Serezhkina, A.V. Vologzhanina, N.A. Neklyudova, V.N. Serezhkin, 2009, published in Kristallografiya,
2009, Vol. 54, No. 1, pp. 65–67. 相似文献
EPR spectra are studied of X-irradiated sodium dichromate crystals grown from an aqueous solution by evaporation at 31°C. Doublet lines of EPR-absorption are attributed to the Cr5+ ions in the CrO43− and CrO3− radicals resulting from radiation decomposition of Cr2O72− and being in the lattice in two unequivalent positions. Hyperfine structure caused by interaction of an unpaired electron with Cr53 nucleus were observed both at liquid nitrogen and room temperatures. For the line, caused by CrO43− radical, gy and Ay directions coincide and angles both between Ax, gx and Az, gz make up ∼ 25°. The spectrum is described by usual spin Hamiltonian for S = 1/2 with following parameters (T = 77 K): for CrO: gz = 1.984, gy = 1.970, gx = 1.961, |Az| = 8.2 · 10−4 cm−1, |Ay| = 13.7 × 10−4 cm−1, |Ax| = 36.1 · 10−4 cm−1; for CrO3−: gz = 1.915, gy = 1.975, gx = 1.985, |Az| = 32.2 · 10−4 cm−1. 相似文献