Growth Defects in Langasite Crystals Observed with White Beam Synchrotron Radiation Topography

Langasite single crystal was grown by the Czochralski method and its perfection was assessed by white beam synchrotron radiation topography. It is found that the growth core and the growth striations are the primary growth defects and they show strong X-ray kinematical contrast in the topographs. Another typical defect in LGS crystal is dislocation. The formation mechanisms of these growth defects in LGS crystals were discussed.

Resistivity Measurement of Molten Olivine in a Laser-Heated Diamond Anvil Cell

The electrical conductivity of molten olivine is studied up to 3720K and 13.2 GPa. The results indicate that the electrical conductivity of molten olivine exhibits the perfect Arrhenius behaviour. The activation energy as well as temperature effect is much smaller than that of the solid olivine. It is expected that the high conductivity zone in the mantle is almost independent of the melting based on our experimental data.

Hydrothermal Synthesis of RbLn_2F_7 and VUV Spectroscopy of RbLn_2F_7:Eu^(3+)(Ln=Gd,Y)

RbLn2F7（Ln = Gd, Y, Er, Yb and Lu）, crystallized in the hexagonal RbEr2F7 structure type, is synthesized by a hydrothermal method. The excitation spectra of Eu^3 ＋ -doped RbGd （Y）2F7 suggest that the oxygen content is very low in the samples obtained by hydrothermal synthesis. Only the f-f transitions of Gd^3＋ ions are observed in the excitation spectrum of RbGd2F7：Eu^3＋ （0.5mol%）, while those of Eu^3＋ ions do not appear. When the Gd^3＋ ions are excited, the absorbed energy is transferred efficiently from Gd^3＋ to Eu^3＋ . The spectra show that the doped Eu^3＋ ions are located in non-centrosymmetric sites in hexagonal RbLn2F7.

Design of 3B3 beamline control system

Both structure and design of the control system in BSRF-3B3 beamline, are discussed and the subsystems are described. The LabVIEW software has advantages on data collecting and real time inspecting. In the process of data collecting, some methods are taken to solve the problems that may be met.

High Bulk Modulus of Nanocrystal γ-Fe2O3 with Chemical Dodecyl Benzene Sulfonic Decoration Under High Pressure

Structural transformation in γ-Fe2O3 nanocrystals (about 1Onm) with dodecyl benzene sulfonic (DBS) coated is studied by using high-pressure energy dispersive x-ray diffraction of synchrotron radiation and high-resolution transmission electron microscopy (HRTEM). Relative to the bulk crystal, the transition pressure showed a decrease while the compressibility increases significantly up to 375 (±9 GPa). HRTEM picture confirmed that there is surface cladding surrounding nanocrystals due to DBS, which formed new special boundaries between nanocrystals and should be different from the ordinary grain boundaries. The experimental results imply that the surface layers of γ-Fe2O3 nanocrystals have strong effect on the compressibility.

Investigation of C_(60) Single Crystal by X-Ray Methods

C_(60) single crystals grown by a single-temperature-gradient technique were characterized by synchrotron radiation white beam x-ray topography and x-ray double crystal diffraction with Cu K_(α1) radiation on conventional x-ray source.The results show that the crystal is rather well crystallized.The x-ray topographies give an evidence of dendritic growth mechanism of C_(60) single crystal,and x-ray double crystal diffraction rocking curve shows that there are mosaic structural defects in the sample.A phase transition at 249±1.5K from a simple cubic to a face centered cubic structure is confirmed by in situ observation of synchrotron radiation white beam x-ray topography with the temperature varing from 230 to 295K.

Local Atomic Structure of Piperidyl Nd Dithiocarbamate

The atomic structure of a novel rare earth complex consisting of Nd and the sulfur-containing ligand pipdtc (C5H10NCS-2) has been studied with extended x-ray absorption fine structure (EXAFS} and x-ray diffraction techniques. The complex of formula Nd(pipdtc)4N(CH3)4 crystallizes in the monoclinic space group P21/n with the following lattice parameters, a = 22.685(2), b = 20.332(2), c = 17.1270(10)Å, β = 100.570(10)o, Z = 8. The calculated density is 1.47g/cm3. A new derivative method is used to remove the post-edge absorption background including the multielectron excitation effect. The EXAFS results demonstrate that there are about eight S and four O atoms around Nd with the Nd-S bond length of 2.916Å and the Nd-O bond length of 2.415Å, respectively. This implies that the powder of this complex is not stable and is easy to oxidize in air. The possible change of structure before and after oxidation is discussed.

Single-crystal Structure of ScAlMgO_4

Crystals of scandium magnesium aluminate, ScAlMgO4, were grown from the melt prepared from stoichiometric quantities of Sc2O3, Al2O3 and MgO. Single-crystal X-ray diffraction indicates that ScAlMgO4 crystallizes in the space group R3 m with a = b = 3.2506（9） A, c = 25.152（8）A, V= 230.16（11）A^3, Z= 3, F（000） = 234,μ = 2.424 cm^-1, the final R = 0.0381 and wR = 0.1061 for 1874 observed reflections with I 〉 2σ（I）. In ScAlMgO4, all Sc atoms are coordinated octahedrally, whereas AI or Mg atoms are forming a tetrahedron, or in a triangular bipyramid if one distant O atom is included. The structure of ScAlMgO4 is characterized by { [AlMgO4]^3-}∞^2 layers parallel to the ab plane, and they are further connected into a 3-dimen-sional framework by Sc atoms via O（1） atoms between the layers.

Designing simple non-fused terthiophene-based electron acceptors for efficient organic solar cells

Low-cost photovoltaic materials are essential for realizing large-scale commercial applications of organic solar cells(OSCs).However,highly efficient OSCs based on low-cost photovoltaic materials are scarce due to a deficiency in understanding the structure-property relationship.Herein,we investigated two low-cost terthiophene-based electron acceptors,namely,3TC8 and 3TEH,with 3,4-bis(octan-3-yloxy)thiophene,differing only in the alkylated thiophene-bridges.Both acceptors exhibit low optical gaps(∼1.43 eV)and possess deep highest occupied molecular orbital(HOMO)levels(∼−5.8 eV).Notably,the single-crystal structure of 3TEH demonstrates highly planar conjugated backbone and strongπ-πstacking between intermolecular terminal groups,attributed to the presence of the bulky alkylated noncovalently conformational locks.Upon utilizing both acceptors to fabricate OSCs,the 3TC8-based device exhibited a power conversion efficiency(PCE)of 11.1%,while the 3TEH-based OSC demonstrated an excellent PCE of 14.4%.This PCE is the highest among OSCs based on terthiophene-containing electron acceptors.These results offer a new strategy for designing low-cost electron acceptors for highly efficient OSCs.

Stable structure of Zr_(49)Cu_(44)Al_7 metallic glass matrix composite with CuZr phase under high pressure up to 40.8 GPa

Ternary Zr49Cu44Al7 metallic glass matrix composite rods with CuZr nano-phase,exhibiting an elastic strain of 1.6% and a high strength of 1.78 GPa,have been manufactured. The structural evaluation of the ternary metallic glass matrix composite under high pressure has been investigated using angle dispersive X-ray diffraction with a synchrotron radiation source. The investigation shows that the amorphous matrix structure is stable under pressures up to 40.8 GPa at room temperature. No pressure induced CuZr nano-phase disappearing or growing was detected. According to the Bridgeman equation of state,the bulk modulus B0 =115.2 GPa has been obtained.

Angular dependent NEXAFS study of the molecular orientation of PTCDA multilayers on Au (111) surface

The molecular orientation of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) multilayers adsorbed on Au (111) surface has been investigated using angular dependent O K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The significant angular dependence of important resonant structures (π* and σ*) reveals that PTCDA molecules adopt an ordered geometry on the substrate surface. The average tilt angle of the PTCDA molecular planes is 27°±10° from the Au (111) surface.

Energy transfer and luminescent properties of Pr^(3+) and/or Dy^(3+) doped NaYF_4 and NaGdF_4

The phosphors that are able to convert vacuum ultraviolet（VUV） light into visible light are demanded for the development of novel displaying and lighting devices.NaYF4：Pr3＋,Dy3＋,NaGdF4：Pr3＋,NaGdF4：Dy3＋and NaGdF4：Pr3＋,Dy3＋were prepared by hydrothermal synthesis method and their luminescent properties in VUV-vis spectral region were investigated at room temperature.For NaYF4：Pr3＋,Dy3＋,no energy transfer process from Pr3＋to Dy3＋was observed.However,the introduction of Gd3＋into the fluoride lattice led to intense Dy3＋emissions upon Pr3＋4f5d state excitation.Gd3＋acted as an intermediate,resulting in efficient energy transfer from Pr3＋to Dy3＋in NaGdF4.Pr3＋transferred most of its energy to Gd3＋,and then the energy was transferred from Gd3＋to Dy3＋.So NaGdF4：Pr3＋,Dy3＋not only took full advantage of the intense Pr3＋4f5d absorption,but converted the VUV excitation light into the near-white emission of Dy3＋.

Optical homogeneity of ADP crystals from rapid growth

ADP (NH4H2PO4) crystals were grown through the traditional method and rapid growth technology. The optical homogeneity of rapid grown ADP crystals was analyzed by laser interferometry and X-ray topography. Laser interferometry revealed sector boundaries at which optical homogeneity decreased dramatically. The main defects that seriously reduced the optical homogeneity of the rapid grown ADP crystal were sector boundaries, growth bands and inclusions. The concentration of Fe and Cr impurities was tested by a plasma emission spectrometer. It was found that the preferential incorporation of metallic impurities into the prismatic faces resulted in high density of growth bands and inclusions, thus reducing optical homogeneity of the prismatic sector.