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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Multicell model of La{sub 3}Ga{sub 5}GeO{sub 14} crystal: A new approach to the description of the short-range order of atoms

The multicell model alternative to the model of mixed atomic sites used now is proposed for a single crystal of La{sub 3}Ga{sub 5}GeO{sub 14} belonging to the langasite family. The multicell consists of four unit cells. In three identical cells of the structure, atoms adapt to the Ge atom occupying one of the two 2d positions on the threefold symmetry axis. In the fourth cell, atoms surround the Ge atom located at the 1a position. The multicell model allows one to study the short-range order of atoms by the methods of classical structure analysis based on Bragg scattering. Four high-resolution data sets measured at 295 and 111.5 K are used in the study. The results are obtained with high relative precision (space group P321, Z = 1; at 295 K a = 8.2020(6) Å and c = 5.1065(6) Å, R/wR = 0.81/0.73% for 3829 unique ref lections; at 111.5 K a = 8.1939(1) Å and c = 5.1022(4) Å, R/wR = 0.85/0.76% for 3880 reflections).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Low-Temperature epitaxial growth of InGaAs films on InP(100) and InP(411)A substrates

The structural and electrical characteristics of In{sub 0.53}Ga{sub 0.47}As epitaxial films, grown in the low-temperature mode on InP substrates with (100) and (411)A crystallographic orientations at flow ratios of As4 molecules and In and Ga atoms of γ = 29 and 90, have been comprehensively studied. The use of InP(411)A substrates is shown to increase the probability of forming two-dimensional defects (twins, stacking faults, dislocations, and grain boundaries), thus reducing the mobility of free electrons, and As{sub Ga} point defects, which act as donors and increase the free-electron concentration. An increase in γ from 29 to 90 leads to transformation of single-crystal InGaAs films grown on (100) and (411)A substrates into polycrystalline ones.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Study of the crystal device for deflecting high-energy proton beams using synchrotron radiation diffraction

Currently, bent silicon single crystals are used at large accelerators to extract and collimate proton beams. A device for multiple deflection of a proton beam based on several bent silicon strips operating in the volume reflection mode has recently been developed. In this device, the bending of silicon strips successively located on the surface of a thick plate is implemented due to the internal stress induced by grooves mechanically formed on the crystal surface (Twyman effect). Topography based on angular scanning and synchrotron radiation was applied to measure the bending of individual deflector strips and the crystal as a whole. The measurement results are compared with the data obtained with a proton beam.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Influence of the nonuniform distribution of electronic defects on the physical properties of garnet crystals

The optical and kinetic properties of Y{sub 3}Fe{sub 5}O{sub 12} garnet single crystals have been investigated. A method for determining the conduction electron concentration in the samples using energy-dispersive X-ray fluorescence analysis has been proposed, which makes it possible to estimate the quality of obtained material based on a unified approach.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Temperature-Induced structural phase transformations in Cu{sub 1.50}Zn{sub 0.30}Te and Cu{sub 1.75}Cd{sub 0.05}Te single crystals

The results of studying the temperature-induced polymorphic phase transformations in Cu{sub 1.50}Zn{sub 0.30}Te and Cu{sub 1.75}Cd{sub 0.05}Te single crystals are presented. The single crystals have been investigated in the range of 290–1100 K using X-ray diffraction analysis. The temperature dependences of the unit-cell parameters, X-ray density, and coefficients of thermal expansion for each polymorphic modification of Cu{sub 1.50}Zn{sub 0.30}Te and Cu{sub 1.75}Cd{sub 0.05}Te single crystals are presented. The influence of cationic substitution (replacement of Cu{sup 2+} with Zn{sup 2+} and Cd{sup 2+} cations) on the phase-formation processes, number of polymorphic modifications, and temperature of structural phase transition in single crystals of these solid solutions is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Polymorphism and structure of Nd{sub 2}MоO{sub 6} single crystals

The tetragonal and monoclinic modifications of Nd{sub 2}MoO{sub 6} single crystals have been investigated by X-ray diffraction. The analysis has been on laboratory sources (2D CCD diffractometers: Xcalibur S (Shared Research Center, Institute of Crystallography, Russian Academy of Sciences) and BRUKER Smart APEX 2 (Shared Research Center, Institute of General and Inorganic Chemistry, Russian Academy of Sciences)) and on a synchrotron radiation source (ESRF, Grenoble, PILATUS@SNBL diffractometer). Local displacements of all atoms in the oxymolybdate structure have been revealed for the first time using electron density difference maps. Possible violation of the translational periodicity in the distribution of Mo and Nd atoms over types is indirectly confirmed, and statistical disorder of oxygen atoms is revealed. The results of the study confirm the previous suggestion that polymorphic transformations occur in oxymolybdates at a very low rate and, apparently, continuously in a wide temperature range. With an increase in temperature, layers undergo ordering according to the cation type as a result of the phase transition from the monoclinic to the tetragonal phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Influence of cation substitution on the polymorphic transformation in Ag{sub 2–х}Cu{sub х}S (х = 0.45, 0.8, and 1.07) crystals

The influence of the concentration substitution of Ag ions for Cu ions in the structure of Ag{sub 2–х}Cu{sub х}S (х = 0.45, 0.8, and 1.07) solid solutions on the temperature of polymorphic phase transitions is demonstrated. The phase composition of Ag{sub 2–х}Cu{sub х}S (х = 0.45, 0.8, and 1.07) solid solutions has been investigated by X-ray diffraction at different temperatures. It is shown that the structure of the polymorphic modification of Ag{sub 0.93}Cu{sub 1.07}S composition and the phase transition temperature correspond to the structure and parameters of AgCuS single crystal. The structures of the modifications of compositions with a high silver concentration (Ag{sub 1.55}Cu{sub 0.45}S and Ag{sub 1.2}Cu{sub 0.8}S) and the phase transitions temperatures differ from the structure and corresponding parameters of AgCuS single crystal.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Algorithm and program for precise determination of unit-cell parameters of single crystal taking into account the sample eccentricity

A technique has been developed to refine the unit-cell parameters of single crystals with minimization of the influence of instrumental errors on the result. The corresponding computational procedure HuberUB is added to the software package of Huber-5042 diffractometer with a point detector and closedcycle helium cryostat Displex DE-202. The parameters of unit cell, its orientation, the goniometer zero angles, the sample eccentricity, the distances in the goniometer, and the radiation wavelength were refined by the nonlinear least-squares method, which allows imposition of constraints on the unit-cell parameters, depending on the crystal symmetry. The technique is approved on a LuB{sub 12} single crystal. The unit-cell parameters are determined in a temperature range of 20–295 K, with an absolute error not larger than 0.0004 Å (the relative error is of ~5 × 10{sup –5}). The estimates of the unit-cell parameters obtained by the proposed method are evidenced to be unbiased. Some specific features of the behavior of parameters in the ranges of 120–140 and 20–50 K are revealed, which correlate with the anomalies of the physical properties of the crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Defect structure and ionic conductivity of as-grown R{sub 1–y}Sr{sub y}F{sub 3–y} (R = Ce, Pr, or Nd) crystals with high SrF{sub 2} content

The structure of defect nonstoichiometric phases of Ce{sub 0.88}Sr{sub 0.12}F{sub 2.88}, Pr{sub 0.85}Sr{sub 0.15}F{sub 2.85}, and Nd0.85Sr0.15F2.85 single crystals has been investigated by X-ray diffraction at room temperature. Crystals R{sub 1–y}Sr{sub y}F{sub 3–y} (R = Ce, Pr, or Nd) belong to the tysonite structural type (LaF{sub 3}), which has two forms (α and β). The morphotropic transition from the trigonal β form of the crystals to the hexagonal α form is confirmed, which was previously found for the first time when analyzing the nonstoichiometric phase of La{sub 1–y}Sr{sub y}F{sub 3–y} with a SrF2 content above 10 mol % (y ≥ 0.1). Temperature dependences of fluorine-ion conductivity are obtained. It is established that the conductivity of the α form of Ce{sub 0.88}Sr{sub 0.12}F{sub 2.88} and R{sub 0.85}Sr{sub 0.15}F{sub 2.85} crystals (R = Pr or Nd) is lower than that for the β form of R{sub 0.95}Sr{sub 0.05}F{sub 2.95} (R = La–Nd) by 1–2 orders of magnitude. The sublattice of fluorine atoms in the α-form crystals is characterized by an elevated (in comparison with the β form) content of vacancies and more uniform structural and dynamic properties, which leads to a decrease in the mean diffusion mobility of fluorine ions and an increase in the ion-transport activation enthalpy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Study of the specific features of single-crystal boron microstructure

A complex study of the structure of β-boron single crystal grown by the floating-zone method, with sizes significantly exceeding the analogs known in the literature, has been performed. The study includes X-ray diffraction analysis and X-ray diffractometry (measurement of pole figures and rocking curves), performed on both laboratory and synchrotron sources; atomic-resolution scanning transmission electron microscopy with spherical aberration correction; and energy-dispersive microanalysis. X-ray diffraction analysis using synchrotron radiation has been used to refine the β-boron structure and find impurity Si atoms. The relative variations in the unit-cell parameters a and c for the crystal bulk are found to be δa/a ≈ 0.4 and δc/c ≈ 0.1%. X-ray diffractometry has revealed that the single-crystal growth axis coincides with the [22̄013] crystallographic axis and makes an angle of 21.12° with the [0001] threefold axis. Electron microscopy data have confirmed that the sample under study is a β-boron crystal, which may contain 0.3–0.4 at % Si as an impurity. Planar defects (stacking faults and dislocations) are found. The results of additional measurements of the temperature dependence of the thermal conductivity of the crystal in the range of 50–300 K are indicative of its high structural quality.

36 MATERIALS SCIENCE↗
DOE OSTI2017

New hardware and software platform for experiments on a HUBER-5042 X-ray diffractometer with a DISPLEX DE-202 helium cryostat in the temperature range of 20–300 K

Huber-5042 diffractometer with a closed-cycle Displex DE-202 helium cryostat is a unique scientific instrument for carrying out X-ray diffraction experiments when studying the single crystal structure in the temperature range of 20–300 K. To make the service life longer and develop new experimental techniques, the diffractometer control is transferred to a new hardware and software platform. To this end, a modern computer; a new detector reader unit; and new control interfaces for stepper motors, temperature controller, and cryostat vacuum pumping system are used. The system for cooling the X-ray tube, the high-voltage generator, and the helium compressor and pump for maintaining the desired vacuum in the cryostat are replaced. The system for controlling the primary beam shutter is upgraded. A biological shielding is installed. The new program tools, which use the Linux Ubuntu operating system and SPEC constructor, include a set of drivers for control units through the aforementioned interfaces. A program for searching reflections from a sample using fast continuous scanning and a priori information about crystal is written. Thus, the software package for carrying out the complete cycle of precise diffraction experiment (from determining the crystal unit cell to calculating the integral reflection intensities) is upgraded. High quality of the experimental data obtained on this equipment is confirmed in a number of studies in the temperature range from 20 to 300 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Evolution of the vanadium pentoxide V{sub 2}O{sub 5} crystal surface after vacuum annealing

A complex study of the (001) cleavage surface of a V{sub 2}O{sub 5} single crystal annealed in vacuum at 450 and 550°C has been performed. Tunnel microscopy of the sample surface annealed in vacuum at 550°C showed the formation of a plane with a corundum structure, reconstructed according to the V{sub 2}O{sub 3} (0001)-(1/√3 × 1/√3)R30° type, on the surface. X-ray photoelectron spectroscopy revealed a significant modification of interatomic bonds in the surface layers of V{sub 2}O{sub 5} single crystal after vacuum annealing at 550°C, which is related to the partial reduction of V{sup 5+} ions and formation of lower vanadium oxides. These modifications lead to a decrease in the electrical resistivity of V{sub 2}O{sub 5} and the occurrence of bending at a temperature of 61.5°С in the temperature dependence of the sample resistance, which is indicative of phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Description of the atomic disorder (local order) in crystals by the mixed-symmetry method

An approach to the description of local atomic disorder (short-range order) in single crystals by the mixed-symmetry method based on Bragg scattering data is proposed, and the corresponding software is developed. In defect-containing crystals, each atom in the unit cell can be described by its own symmetry space group. The expression for the calculated structural factor includes summation over different sets of symmetry operations for different atoms. To facilitate the search for new symmetry elements, an “atomic disorder expert” was developed, which estimates the significance of tested models. It is shown that the symmetry lowering for some atoms correlates with the existence of phase transitions (in langasite family crystals) and the anisotropy of physical properties (in rare-earth dodecaborides RB{sub 12}).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Hydrothermal Synthesis, Crystal Structure, and Photoluminescent Properties of Li[UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 3}[Co(H{sub 2}O){sub 6}]

Single crystal of Li[UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 3}[Co(H{sub 2}O){sub 6}] was prepared and found to crystallize in the monoclinic crystal system in the sp. gr. C2/c, with Z = 2, and unit cell parameters a = 22.1857(15) Å, b = 13.6477(8) Å, c = 15.6921(10) Å, β = 117.842(9)°, V = 4201.3(4) Å{sup 3}. The crystal was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The single crystal X-ray diffraction analysis revealed that the crystal has a lamellar structure in which a cobalt hydrate is sandwiched within the Li[UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 3}{sup 2-} chains. Furthermore, the room temperature photoluminescence spectrum of the complex was investigated in the solid state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Synthesis and Crystal Structure of 7,8,9,10-Tetrahydro-2-bromo-cyclohepta[b]indol-6(5H)-one

The title compound, C{sub 13}H{sub 12}BrNO, was synthesized and characterised by IR, {sup 1}H and {sup 13}C NMR spectroscopy. The proposed structure was confirmed by single crystal X-ray diffraction. The single crystal data revealed that the compound crystallizes in the triclinic system, sp. gr. P1, with Z = 2. The sevenmembered ring exhibits a slightly distorted envelope conformation. N–H···O hydrogen bonds form a centrosymmetric dimer, these interactions create a stair-like chain of molecules that interacts only loosely with neighbouring chains via van der Waals interactions, and C–H···π contacts are found in the crystal structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Experimental (X-ray, FT-IR, and UV-Vis Spectroscopy) and Theoretical Methods (DFT Study) of N'-(Dipyridin-2-ylmethylene)-4-methylbenzenesulfonohydrazide

A new hydrazone derivative was synthesized and characterized by IR, UV-Vis spectroscopy, elemental analysis and single-crystal X-ray diffraction. The compound was established to reveal antibacterial activity. The compound (C{sub 18}H{sub 16}N{sub 4}O{sub 2}S) crystallizes in monoclinic crystal system with C2/c space group. The molecular structure is stabilized by a C–H···O intermolecular hydrogen bond. Quantum chemical calculations based on DFT/B3LYP/6-31G(d, p) were carried out and the results were compared with the experimental data. The calculated vibrational frequencies were used to determine the types of molecular motions associated with each of the observed experimental bands. UV-Vis absorption spectra of the compound calculated by TD-DFT have been ascribed to their corresponding molecular structure and electron transitions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Synthesis and Structural Analysis of 2-Cyanophenyl Phenacyl Ether

Molecular and crystal structure of 2-cyanophenyl phenacyl ether, C{sub 15}H{sub 11}O{sub 2}N, have been determined by single crystal X-ray diffraction study. The title compound is monoclinic, with a = 4.4334(4) Å, b = 10.7677(11) Å, c = 12.7779(11) Å, β = 99.806(8)°, Z = 2, sp. gr. P2{sub 1}. The crystal structure is stabilized by C–H···O inter-molecular interactions. In order to clarify the electron delocalization on the whole molecule and determine the active sites of the title compound, DFT calculations and NBO analysis were performed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Synthesis, Spectroscopy, and α-Glucosidase Inhibitory Activity of 3-Substituted Hydrazone Derivatives and Crystal Structure of (1E,2E)-1,2-Bis[1-(3-methoxyphenyl)ethylidene]hydrazone

Six 3-substituted hydrazone derivatives [R = −OCH{sub 3} (1), −NH{sub 2} (2), −NO{sub 2} (3), −F (4), −Cl (5), and −Br (6)] were synthesized by condensation reaction. Their structures were elucidated by {sup 1}H NMR, FT-IR and UV-Vis spectroscopy. The synthesized compounds were further evaluated for their α-glucosidase inhibitory activity. Strong activity was found for 1 and 3. The crystal structure of 1 was determined by single crystal X-ray diffraction: a = 6.9743(1) Å, b = 18.3627(3) Å, c = 12.0207(2) Å, β = 96.087(1)o, sp. gr. P2{sub 1}/c, Z = 4. The molecule of 1 is twisted with the dihedral angle between the two phenyl rings being 51.91(4)°. In the crystal packing, the molecules are linked into chains by C–H···π interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗