Ordered Arrangement Of Atoms Research Articles

The intrinsic Josephson effect of Bi-2212 superconducting thin films prepared by sol-gel method

In this paper, Bi2Sr2Ca1Cu2O8+σ (Bi-2212) superconducting thin films was prepared by using a sol-gel method on a LaAlO3 (LAO) single crystal substrate, with acetates of bismuth, strontium, calcium, and copper as the starting raw materials. A step structure was specifically designed to measure the intrinsic Josephson effect. The microstructure of the Bi-2212 thin films and their epitaxial growth on the LAO substrate were analyzed by a Cs-corrected transmission electron microscope (Cs-TEM) with an atomic-level resolution and the electrical properties were measured. The results showed that the prepared Bi-2212 thin films had good epitaxial growth characteristics and good in-plane and out-plane growth texture and that its critical transition temperature, Tc, was 87 K. The interface between the substrate and the film was well-defined; the films grow epitaxially on the substrate from the CuO layer, with a highly ordered atom arrangement. The I–V characteristic curve of the prepared step micro-bridging sample showed zero-voltage overcurrent phenomenon, and the critical current was 2.3 mA. In addition, multiple current-voltage jumps were observed on the curve, indicating that the prepared biaxial texture thin films showed the intrinsic Josephson effect.

Atomic structure revolution and excellent performance improvement of composites induced by laser ultrafine-nano technology

Carbon nanotubes (CNTs) reinforced high-entropy alloy composites (HEACs) were fabricated on a TA2 titanium alloy by mean of a laser melting deposition (LMD) of the FeCoCrAlCu-(nano-SiB6)-(Ni/Ag-coated CNTs) mixed powders, noting that large quantities of the ultrafine nanocrystals (UNs) were formed, portion of them were able to obtain the enormous energy from laser beam, which were able to permeate into the original ordered atom arrangement due to the high diffusion rates and their ultrafine microstructure. In substance, partial UNs can destroy the balanced state of atoms, increasing significantly the free energy of the crystal boundaries. Such CNTs/UNs modified LMD composites showed the better corrosion/high-temperature oxidation resistance properties than those of the TA2 alloy. Identification of the synthetic UNs in such LMD HEACs, more importantly the UNs transition effect, contributes theoretical/experimental basis to upgrade the quality of the industrial light alloy.

Structure and preferred orientation of primary phases of Ni-Al-Co-based alloy alloyed by Rhenium after annealing and creep exposure

The present paper investigates phase composition and fine structure of Ni-Al-Co-based alloy alloyed by Rhenium (Re) (~3 at.%), as well as studies preferred orientation of the given alloy primary phases by means of scanning electron microscopy and X-ray diffraction analysis. The original state was given as the alloy which underwent a complete cycle of heat treatment: stepwise homogenization, cooling, annealing, and cooling at 100°C/min back to room temperature. The alloy was further subject to annealing at 1000°C for 105 h and 968 h. It was also exposed to creep experiments at the same temperature for 105 h (loading 320 MPa), and for 968 h (220 MPa). γ- and γ′-phases were established to be the primary phases in both states of face-centered cubic crystal lattice. γ′-phase (phase with ordered atom arrangement having L12 superstructure) was the primary phase in all states of the alloy. Investigations showed that Re being able not to dissolve in the primary phases served as a phase-forming element. Phase composition and phase morphology were studied. The influence of high-temperature annealing and creep on superalloy structure and morphology of γ′-phase were defined. The influence of creep on the structure was proven to be different from the annealing effect. First, creep generated larger dissipation of orientations than annealing. Second, anisotropy of γ′-phase cuboids could be observed at meso-level. Cuboids partially joined together. Third, spheroidized cuboids could be often met after creep.

Structure and Phase Composition of Ni–Al–Cr Alloy Alloyed by Rhenium and Lanthanum

The paper presents the transmission and the scanning electron microscope investigations of the phase composition and fine structure of Ni–Al–Cr-based alloy alloyed by rhenium and lanthanum. The alloy is prepared by the directional crystallization technique and then subjected to 1150°С annealing during 1 hour. It is shown that γ- and γ′-phases are major and have a face-centered cubic crystal system. Solid solutions of γ- and γ′-phase have a disordered and an ordered atom arrangement, respectively. The latter has L12 superstructure. It is found that rhenium and lanthanum alloying leads to the structural modification of γ′-phase quasi-cuboids. Not dissolving in major phases, rhenium and lanthanum are phase-formation elements and form σ-phase. The phase composition and morphology of these phases are studied and described.

Electron-density distribution and disordered crystal structure of 12H-SiAlON, SiAl5O2N5

The crystal structure of SiAl5O2N5was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is hexagonal with space groupP63/mmc(Z = 2). The unit-cell dimensions area = 0.303153(3) nm,c = 3.28153(3) nm, andV = 0.261178(5) nm3. The initial structural model was successfully derived by the direct methods and further refined by the Rietveld method. The final structural model showed the positional disordering of two of the four (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF wereRwp = 5.00%,S(=Rwp/Re) = 1.25,Rp = 3.76%,RB = 1.26%, andRF = 0.90%. The disordered crystal structure was successfully described by overlapping four types of domains with ordered atom arrangements. The distribution of atomic positions in each of the domains can be achieved in the space groupP63mc. Two of the four types of domains are related by a pseudo-symmetry inversion, and the two remaining domains also have each other the inversion pseudo-symmetry.

Electron density distribution and disordered crystal structure of 8H-SiAlON, Si3−xAl1+xOxN5−x (x~2.2)

The 8H-SiAlON crystal with general formula Si3−xAl1+xOxN5−x was characterized using laboratory X-ray powder diffraction (CuKα1), transmission electron microscopy and energy dispersive X-ray spectroscopy. The [Si: Al] molar ratios were determined to be [0.21(1): 0.79(1)], corresponding to x=2.2(1). The Si0.8(1)Al3.2(1)O2.2(1)N2.8(1) compound is hexagonal with space group P63/mmc (Z=2). The unit-cell dimensions are a=0.298877(8)nm, c=2.30872(5)nm and V=0.178602(8)nm3. The initial structural model was successfully derived by the charge-flipping method and further refined by the Rietveld method. The final structural model showed the positional disordering of two of the three (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were Rwp=4.74%, S (=Rwp/Re)=1.30, Rp=3.40%, RB=1.04% and RF=0.74%. The disordered crystal structure was successfully described by overlapping four types of domains with ordered atom arrangements. The distribution of atomic positions in each of the domains can be achieved in the space group P63mc. Two of the four types of domains are related by a pseudo-symmetry inversion, and the two remaining domains also have each other the inversion pseudo-symmetry.

Electron density distribution and disordered crystal structure of 15R-SiAlON, SiAl4O2N4

The crystal structure of SiAl4O2N4 was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is trigonal with space group R3̄m. The hexagonal unit-cell dimensions (Z=3) are a=0.301332(3)nm, c=4.18616(4)nm and V=0.3291825(5)nm3. The initial structural model was successfully derived by the charge-flipping method and further refined by the Rietveld method. The final structural model showed the positional disordering of one of the three (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were Rwp=5.05%, S (=Rwp/Re)=1.21, Rp=3.77%, RB=1.29% and RF=1.01%. The disordered crystal structure was successfully described by overlapping three types of domains with ordered atom arrangements. The distribution of atomic positions in one of the three types of domains can be achieved in the space group R3̄m. The atom arrangements in the other two types of domains are noncentrosymmetrical with the space group R3m. These two structural configurations are related by the pseudo-symmetry inversion.

Electron density distribution and crystal structure of 21R-AlON, Al7O3N5

The crystal structure of Al7O3N5was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is trigonal with a space groupR3m(centrosymmetric). The hexagonal unit-cell dimensions (Z = 3) area = 0.305 06(1) nm,c = 5.7216(1) nm, andV = 0.461 11(2) nm3. The initial structural model was derived by the charge-flipping method and refined by the Rietveld method. The final structural model showed the positional disordering of two of the four Al sites. The maximum-entropy method-based pattern fitting method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The disordered crystal structure was successfully described by overlapping five types of domains with ordered atom arrangements. The distribution of atomic positions in one of the five types of domains can be achieved in the space groupR3m. The atom arrangements in the four other domains are non-centrosymmetric with the space groupR3m. Two of the four types of domains are related by a pseudo-symmetrical inversion, and the two remaining domains also have each other in the inversion pseudo-symmetry.

Electron density distribution and crystal structure of 27R-AlON, Al9O3N7

The crystal structure of Al 9 O 3 N 7 was characterized by laboratory X-ray powder diffraction (Cu K α 1 ). The title compound is trigonal with space group R 3̄ m (centrosymmetric). The hexagonal unit-cell dimensions ( Z =3) are a =0.30656(2) nm, c =7.2008(3) nm and V =0.58605(5) nm 3 . The initial structural model was derived by the powder charge-flipping method and subsequently refined by the Rietveld method. The final structural model showed the positional disordering of two of the five types of Al sites. The maximum-entropy method-based pattern fitting method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The disordered crystal structure was successfully described by overlapping five types of domains with ordered atom arrangements. The distribution of atomic positions in one of the five types of domains can be achieved in the space group R 3 ¯ m . The atom arrangements in the four other domains are noncentrosymmetric with the space group R 3 m . Two of the four types of domains are related by a pseudo-symmetry inversion, and the two remaining domains also have each other the inversion pseudo-symmetry. The very similar domain structure has been also reported for 21 R -AlON (Al 7 O 3 N 5 ) in our previous study. A bird’s eye view of electron densities up to 50% (0.074 nm −3 ) of the maximum on the plane parallel to (110) with the corresponding atomic arrangements of Al 9 O 3 N 7 . • Crystal structure of Al 9 O 3 N 7 is determined by laboratory X-ray powder diffraction. • The atom arrangements are represented by the split-atom model. • The maximum-entropy method-based pattern fitting method is used to confirm the validity of the model. • The disordered structure is described by overlapping five types of domains with ordered atom arrangements.

Physical properties of non-centrosymmetric Ni2Zn11

X-ray single crystal data for Ni2Zn11 confirm an ordered atom arrangement with Ni-atoms in the tetrahedral site 8c of space group I4¯3m (a = 0.89110(8) nm; RF = 0.018) as an ordered variant of the non-centrosymmetric γ-brass phases (Cu5Zn8-type). Ultrasonic experiments, a study of the electrical resistivity as well as of the heat capacity of binary Ni2Zn11 reveal a rather brittle metallic compound, with a bulk modulus matching typical intermetallics. The absence of both superconductivity as well as of long range magnetic order in the temperature range from 350 mK to room temperature is considered to be a consequence of the rather low electronic density of states right at the Fermi energy.

The ternary system: silicon–uranium–vanadium

Phase equilibria in the system Si–U–V were established at 1100 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed, U 2V 3Si 4 and (U 1− x V x ) 5Si 3, for which the crystal structures were elucidated by X-ray powder data refinement and found to be isotypic with the monoclinic U 2Mo 3Si 4-type (space group P2 1/ c; a = 0.6821(3), b = 0.6820(4), c = 0.6735(3) nm, β = 109.77(1)°) and the tetragonal W 5Si 3-type (space group I4/ mcm, a = 1.06825(2), c = 0.52764(2) nm), respectively. (U 1− x V x ) 5Si 3 appears at 1100 °C without any significant homogeneity region at x ∼ 0.2 resulting in a formula U 4VSi 3 which corresponds to a fully ordered atom arrangement. DTA experiments clearly show decomposition of this phase above 1206 °C revealing a two-phase region U 3Si 2 + V 3Si. At 1100 °C U 4VSi 3 is in equilibrium with V 3Si, V 5Si 3, U 3Si 2 and U(V). At 800 °C U 4VSi 3 forms one vertex of the tie-triangle to U 3Si and V 3Si. Due to the rather high thermodynamic stability of V 3Si and the corresponding tie-lines V 3Si + liquid at 1100 °C and V 3Si + U(V) below 925 °C, no compatibility exists between U 3Si or U 3Si 2 and vanadium metal.

Crystal Chemistry and Magnetism of Ternary Actinoid Boron Carbides UB 1- xC 1+ x and U 1- xMxB 2C with M = Sc, Lu, and Th

Within the homogeneous range of uranium monocarbide UB 1- x C 1+ x , the crystal structures of stoichiometric UBC and of the carbon-rich solid solution UB 0.78C 1.22, have been refined from single-crystal X-ray counter data. From X-ray analysis crystal symmetry in both cases is consistent with the centro-symmetric space group Cmcm and there are no indications of superstructure formation. In contrast to the fully ordered atom arrangement revealed for stoichiometric UBC ( a = 0.35899(4), b = 1.19781(12), c = 0.33474(3) nm), random occupation by boron and carbon atoms is observed for the boron site in UB 0.78C 1.22 ( a = 0.35752(4), b = 1.18584(3), c = 0.33881(4) nm). For 279(278) reflections (|F 0| > 3σ) the obtained reliability factors R x = ∑|ΔF|/∑| F 0| were R x = 0.069 for UBC and R x = 0.050 for UB 0.78C 1.22. Neutron powder diffraction experiments at 9 and 295 K unambiguously revealed full occupancy by the nonmetal atoms in UB 0.78C 1.22 and prove the statistical occupation of B and C atoms in the B-sites. For the orthorhombic symmetry Cmcm, refinement was not better than R 1 = 0.044. A model calculation in monoclinic symmetry C12/ m1, however, resulted in a significant reduction of the residual value to R 1 = 0.030, releasing spatial constraints on the boron atoms. Thus the boron-boron chain in Cmcm (B-B = 0.1874 nm) is dissolved into boron pairs (B-B = 0.1706 nm) which are loosely bound at a distance of 0.2043 nm. The formation of C-B-B-C groups corresponds to the structure types of ThBC and Th 3B 2C 3. The magnetic behavior has been investigated in the temperature range from 4.2 K to 1000 K for UB 1- x C 1+ x (UBC-type) and U 1- x M x B 2C (ThB 2C-type for the high temperature modification and 1-UB 2C-type for the low temperature modification) with U partially substituted by Th or Sc, Lu. From magnetic susceptibilities, the alloys UB 1- x C 1+ x reveal temperature independent paramagnetism with typical intermediate valence fluctuation behavior ( T SF ∼ 350 K). ThB 2C and 1-UB 2C both are temperature independent paramagnets, whereas h-UB 2C is a ferromagnet with the rather high Curie temperature T M = 80(2) K. T M and the saturation magnetiziation per U atom both successively decrease on substitution of U by Th, Sc, or Lu in UB 2C, whereas the U-moments remain practically unchanged at μ eff(U) ∼ 1.9 μ B. Uranium L 3-XANES (X-ray Absorption Near Edge Structure) spectroscopy revealed increased d-band localization, comparable to uranium-transition metal alloys, in nonmagnetic UB 1- x C 1+ x ( x = 0, 0.22). No superconductivity was observed down to 1.5 K; no hydrogen uptake was observed for UB 2C and ThB 2C even under hydrogen pressures as high as 7 × 10 7 Pa at 670 K.

Crystal structure of the ordered Nb 10Ge 7 phase

The structure of a new ordered phase, Nb 10Ge 7 (or Nb 5Ge 3Ge 0.5; trigonal), is described on the basis of electron microscopic and electron diffraction data. The new phase was found in a Nb Ge tape prepared by the coevaporation technique. The new structure can be derived from the hexagonal D8 8-structure of Nb 5Ge 3 by periodically inserting Ge-atoms at octahedral sites. The lattice parameters of this structure can be described as follows, using the lattice parameters of the D8 8-structure a= √3 ·a Nb 5Ge 3(D 88 and c=C Nb 5Ge 3(D 88) in hexagonal description. The grains of this phase are usually elongated along the c-direction. Structural data of the new phase: Nb 10Ge 7,trigonal, hP51, P 3¯2/ml,a= 1.337nm,c= 0.537nm,Z= 3,V Nb 10Ge 7 ≈ 3V Nb 5Ge 3(D 88) . The structure represents a new structure type with an ordered atom arrangement, intermediate between the Mn 5Si 3 type and the Ti 5Ga 4 type, in which the octahedral sites are only partly occupied.

Some characteristics of an inverted magnetron cold cathode ionization gauge with dual feedthroughs: N T Peacock and R N Peacock,J Vac Sci Technol,A6, 1988, 1141–1144

Phase equilibria in the system Si–U–V were established at 1100 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed, U2V3Si4 and (U1−xVx)5Si3, for which the crystal structures were elucidated by X-ray powder data refinement and found to be isotypic with the monoclinic U2Mo3Si4-type (space group P21/c; a = 0.6821(3), b = 0.6820(4), c = 0.6735(3) nm, β = 109.77(1)°) and the tetragonal W5Si3-type (space group I4/mcm, a = 1.06825(2), c = 0.52764(2) nm), respectively. (U1−xVx)5Si3 appears at 1100 °C without any significant homogeneity region at x ∼ 0.2 resulting in a formula U4VSi3 which corresponds to a fully ordered atom arrangement. DTA experiments clearly show decomposition of this phase above 1206 °C revealing a two-phase region U3Si2 + V3Si. At 1100 °C U4VSi3 is in equilibrium with V3Si, V5Si3, U3Si2 and U(V). At 800 °C U4VSi3 forms one vertex of the tie-triangle to U3Si and V3Si. Due to the rather high thermodynamic stability of V3Si and the corresponding tie-lines V3Si + liquid at 1100 °C and V3Si + U(V) below 925 °C, no compatibility exists between U3Si or U3Si2 and vanadium metal.

An optical neural society of mind: [formula omitted], Center for Applied Optics, University of Alabama in Huntsville, Huntsville, Alabama 35899

Within the homogeneous range of uranium monocarbide UB1-xC1+x, the crystal structures of stoichiometric UBC and of the carbon-rich solid solution UB0.78C1.22, have been refined from single-crystal X-ray counter data. From X-ray analysis crystal symmetry in both cases is consistent with the centro-symmetric space group Cmcm and there are no indications of superstructure formation. In contrast to the fully ordered atom arrangement revealed for stoichiometric UBC (a = 0.35899(4), b = 1.19781(12), c = 0.33474(3) nm), random occupation by boron and carbon atoms is observed for the boron site in UB0.78C1.22 (a = 0.35752(4), b = 1.18584(3), c = 0.33881(4) nm). For 279(278) reflections (|F0| > 3σ) the obtained reliability factors Rx = ∑|ΔF|/∑|F0| were Rx = 0.069 for UBC and Rx = 0.050 for UB0.78C1.22. Neutron powder diffraction experiments at 9 and 295 K unambiguously revealed full occupancy by the nonmetal atoms in UB0.78C1.22 and prove the statistical occupation of B and C atoms in the B-sites. For the orthorhombic symmetry Cmcm, refinement was not better than R1 = 0.044. A model calculation in monoclinic symmetry C12/m1, however, resulted in a significant reduction of the residual value to R1 = 0.030, releasing spatial constraints on the boron atoms. Thus the boron-boron chain in Cmcm (B-B = 0.1874 nm) is dissolved into boron pairs (B-B = 0.1706 nm) which are loosely bound at a distance of 0.2043 nm. The formation of C-B-B-C groups corresponds to the structure types of ThBC and Th3B2C3. The magnetic behavior has been investigated in the temperature range from 4.2 K to 1000 K for UB1-xC1+x (UBC-type) and U1-xMxB2C (ThB2C-type for the high temperature modification and 1-UB2C-type for the low temperature modification) with U partially substituted by Th or Sc, Lu. From magnetic susceptibilities, the alloys UB1-xC1+x reveal temperature independent paramagnetism with typical intermediate valence fluctuation behavior (TSF ∼ 350 K). ThB2C and 1-UB2C both are temperature independent paramagnets, whereas h-UB2C is a ferromagnet with the rather high Curie temperature TM = 80(2) K. TM and the saturation magnetiziation per U atom both successively decrease on substitution of U by Th, Sc, or Lu in UB2C, whereas the U-moments remain practically unchanged at μeff(U) ∼ 1.9 μB. Uranium L3-XANES (X-ray Absorption Near Edge Structure) spectroscopy revealed increased d-band localization, comparable to uranium-transition metal alloys, in nonmagnetic UB1-xC1+x (x = 0, 0.22). No superconductivity was observed down to 1.5 K; no hydrogen uptake was observed for UB2C and ThB2C even under hydrogen pressures as high as 7 × 107 Pa at 670 K.