Magnetic torque of κ-(BEDT-TTF)2Cu(NCS)2 single crystals

The magnetic torque ofκ-(BEDT-TFF)₂Cu(NCS)₂ was measured as a function of field directionθ with respect to thea ^*-axis under constant magnetic fields,H, up to 8 kOe in the temperature range from 1.3 to 8 K. A sharp cusp, C₁, in the irreversible region was found atθ _c1 near theH∥bc-plane between 1.3 and 7 K. In addition, extra cusps, C₂ and C₃, were observed atθ _c2 andθ _c3, respectively, between 2.5 and 6 K. At each temperature, the perpendicular component ofH giving each cusp is kept constant as $H\cos \theta _{cn} = const \equiv H_{cp_n } (n = 1,2,3),$ i.e., cusps C₁, C₂, and C₃ are ruled by the characteristic field perpendicular to thebc-planeH _cp1,H _cp2, andH _cp3, respectively. These behaviors are almost the same as those we found in the oxide superconductor Bi₂Sr₂CaCu₂O₈. These results suggest that the cusps are intrinsic for irreversible vortex states of these layered superconductors.     

Physicochemical Properties of (CuAlSe2)x(2ZnSe)1 – xSolid Solutions

(CuAlSe₂) _x (2ZnSe)_{1 – x} solid solutions were prepared by a single-zone method. According to x-ray diffraction characterization, the solid solutions had the chalcopyrite structure for x> 0.7 and sphalerite structure for x< 0.7. CuAlSe₂, ZnSe, and (CuAlSe₂) _x (2ZnSe)_{1 – x} crystals were grown by chemical vapor transport and were used for microhardness tests and transmission measurements near the fundamental edge. The results demonstrate that the microhardness and band gap of the solid solutions pass through a maximum and minimum, respectively.     

Crystal Structure of Neptunium(V) Phthalate (NpO2)2(OOC)2C6H4·4H2O

The crystal structure of (NpO₂)₂(OOC)₂C₆H₄·4H₂O [rhombic cell: a = 15.937(3), b = 26.922(5), c = 8.020(2) Å, space group Pbcn, Z = 8, V = 3441.0(12) ų, d _calc = 2.988 g cm^{- 3}, CAD4, MoK , graphite monochromator, 2934 independent reflections; R ₁ = 0.0352, wR ₂ = 0.0951] was studied. The structure consists of NpO₂ ⁺ cations, H₄C₆(COO)₂ ^{2 -} anions, and molecules of coordinated and crystallization water. The crystal lattice involves neutral layers [(NpO₂)₂(OOC)₂C₆H₄(H₂O)₃] _n parallel to the {101} plane. The dioxocations in these layers are bonded to each other to form cationic networks [the Np···Np distance is 3.911(1)-4.202(1) Å]. The coordination polyhedra of Np(1) and Np(2) are pentagonal bipyramids (CN 7). The point group of the neptunyl(V) groups is close to D _h. These groups are bidentate ligands in the cation-cation interaction. The Np = O bond lengths are 1.852(6) [Np(1)-O(1)], 1.849(7) [Np(1)-O(2)], 1.845(7) [Np(2)-O(3)], and 1.841(7) Å [Np(2)-O(4)]; the O = Np = O bond angles are 178.6(3)° [O(2)-Np(1)-O(1)] and 177.4(3)° [O(3)-Np(2)-O(4)]. The equatorial plane of the Np(1) bipyramid consists of two oxygen atoms of adjacent Np(2)O₂ ⁺ dioxocations, two water molecules, and a single oxygen atom of the phthalate anion. The equatorial plane of the Np(2) bipyramid consists of two oxygen atoms of adjacent Np(1)O₂ ⁺ dioxocations, two oxygen atom of the phthalate anion, and a single water molecule. The bond lengths in the equatorial plane of the bipyramid lie in the following ranges: Np-Oyl 2.373(7)-2.437(7) Å (average 2.397 Å) , Np-Ophth 2.360(7)-2.474(7) Å (average 2.431 Å), and Np-Owater 2.534(8)-2.558(9) Å (average 2.544 Å). The phthalate anions are tridentate bridging ligands binding neptunium atoms only within a single cationic network.     

Probing the Upper Critical Field of κ-(BEDT-TTF)2Cu(NCS)2

Studies of heat conduction and microwave absorption in the vortex state of -(BEDT-TTF)₂Cu(NCS)₂ reveal some of the specific aspects of superconductivity in this system. Moreover they allow us to probe the destruction of bulk superconductivity by a magnetic field. The two set of results yield identical magnitudes for the upper critical field with a temperature dependence distinctly different from the one suggested by the onset of resistive transition.     

Microwave response of Josephson plasma in the mixed state of κ-(BEDT-TTF)2Cu(NCS)2

A cavity perturbation technique is used to measure the magnetic-field dependence of surface impedance at 24 and 41 GHz in superconducting -(BEDT-TTF)₂Cu(NCS)₂ single crystals. A peak structure in the surface resistance R_s(H) is observed (1) below T_c, (2) when microwave electric field is perpendicular to the superconducting layer, and (3) at higher magnetic field for the lower measurement frequency (anticyclotronic behavior). These observations are identified as the Josephson plasma mode. The peak field increases as the temperature is lowered even below the irreversibility line in contrast to the case of Bi₂Sr₂CaCu₂O_8+y.     

Experimental investigation of the self- and N(2)-broadened continuum within the ν(2) band of water vapor

We present an experimental study of the self- and N(2)-broadened H(2) O continuum in microwindows within the ν(2) fundamental centered at ~1600 cm(-1). The continuum is derived from transmission spectra recorded at room temperature with a BOMEM Fourier transform spectrometer at a resolution of ~0.040 cm(-1). Although we find general agreement with previous studies, our results suggest that there is significant near-wing super-Lorentzian behavior that produces a highly wave-number-dependent structure in the continuum as it is currently defined.     

The mixed state of theκ-(BEDT-TTF)2Cu(NCS)2 organic superconductor

The quasi-2D organic superconductor -(BEDT-TTF)₂Cu(NCS)₂ presents properties in the superconducting state which are similar to most anisotropic high-T_c compounds. The smaller upper critical fields (100kOe) enable us to study the entire (H, T) phase diagram by electrical transport measurements: large superconducting fluctuations lead to a broadening of the normal-superconducting transition as well as to the presence of a phase transition line between a solid and a viscous liquid phase. In low magnetic fields, the displacement of the vortices in the liquid phase is due to the creation of double kinks in the flux lines.     

Magnetoresistivity in the vortex liquid phase ofκ-(BEDT-TTF)2Cu(NCS)2

We report single crystal magnetoresistivity measurements of the organic superconductor -(BEDT-TTF)₂Cu(NCS)₂ in magnetic fields applied perpendicularly to the superconducting planes. We present an analysis of the behavior of the resistivity in the vortex liquid phase. It turns out, that at high temperatures and sufficiently low fields the vortex liquid phase can be described as a very viscous vortex liquid of 3D vortices with activation energies arising from generations of vortex-doublekinks. Quantitatively a value of the superconducting anisotropy parameter = _ab/_c 80 can be derived from the measurements presented here.     

Photolithography of amorphous films of (η5-C5H5)2Ti(N3)2 on silicon (111) resulting in TiO2: The mechanism of the photodeposition reaction

Photolithography to produce TiO₂ patterns from amorphous films of (⁵-C₅H₅)₂Ti(N₃)₂ has been demonstrated. The efficiency of the reaction has been measured yielding a quantum yield of 0.025. The mechanism of the photoreactions of (⁵-C₅H₅)₂Ti(N₃)₂ has been studied using Fourier transform-infrared spectroscopy in both a low-temperature 1,2-epoxyethylbenzene glass and as surface films. In each case the primary photochemical process was found to be loss of a single azido group. The result of subsequent photolysis was found to be dependent upon medium and temperature. In the low-temperature glass no further photochemistry was observed. The exhaustive photolysis of films at 20 K, or room temperature, under a vacuum or in air led to loss of all ligands and the formation of TiO₂.     

Synthesis of β-Mo(2)C thin films

Thin films of stoichiometric β-Mo(2)C were fabricated using a two-step synthesis process. Dense molybdenum oxide films were first deposited by plasma-enhanced chemical vapor deposition using mixtures of MoF(6), H(2), and O(2). The dependence of operating parameters with respect to deposition rate and quality is reviewed. Oxide films 100-500 nm in thickness were then converted into molybdenum carbide using temperature-programmed reaction using mixtures of H(2) and CH(4). X-ray diffraction confirmed that molybdenum oxide is completely transformed into the β-Mo(2)C phase when heated to 700 °C in mixtures of 20% CH(4) in H(2). The films remained well-adhered to the underlying silicon substrate after carburization. X-ray photoelectron spectroscopy detected no impurities in the films, and Mo was found to exist in a single oxidation state. Microscopy revealed that the as-deposited oxide films were featureless, whereas the carbide films display a complex nanostructure.     

Magnetization anomaly and mixed state phase diagram of κ-(BEDT-TTF)2Cu(NCS)2

Local magnetization measurements using micro Hall probes were carried out on a quasi two-dimensional organic superconductor -(BEDT-TTF)₂Cu(NCS)₂. Peak structures in the local magnetization hysteresis loops were found at around 50 G. We ascribe this anomaly to the field-induced decomposition of vortex lines into pancake vortices, which is found in a high temperature superconductor Bi₂Sr₂CaCu₂O_8+y. Mixed state phase diagram in -(BEDT-TTF)₂Cu(NCS)₂ is compared with that in Bi₂Sr₂CaCu₂O_8+y.     

Interaction of An(VI) (An = U, Np, Pu) and Np(V) with 2,3-pyridinedicarboxylic (quinolinic) acid (H2Quin): Complexation in aqueous solutions, synthesis and structure of the complexes [UO2(HQuin)2], [(NpO2)2(HQuin)2(C6H4NO3)2]·2H2O, and [PuO2Quin(H2O)]

Complexation of An(VI) (An = U, Np, Pu), and Np(V) with 2,3-pyridinedicarboxylic (quinolinic, H₂Quin) acid in aqueous solutions was studied. Np(V) can form 1: 1 and 1: 2 complexes, and An(VI), also 1: 3 complexes (at pH ? 6 and [H₂Quin] ? 0.1 M). Quinolinate ion can coordinate to actinide(VI) and (V) ions in solutions in different modes. The apparent stability constants of the complexes in a wide pH range and the concentration stability constants of the An(VI) complexes were measured. In the series from Pu(VI) to U(VI), the stability of the complexes slightly increases. Crystalline complexes [UO₂(HQuin)₂], [(NpO₂)₂(HQuin)₂(HL)₂]·2H₂O (HL is N-protonated 2-hydroxypyridine-3-carboxylic acid anion), and [PuO₂Quin(H₂O)] were synthesized, and their structures were determined by single crystal X-ray diffraction. Different types of coordination of quinolinate ions to actinide ions are also observed in the crystalline complexes.     

Magneto-Structural Studies of 2-(2-Ammoniumethyl)-1-méthyl Pyrrolidinium Tetrachlorocuprate (II)

The (C₇H₁₈N₂)CuCl₄ compound crystallized in the orthorhombic system with space group P 2₁2₁2₁ and the following unit cell are: a=7.353(3), b=11.608(5), c=16.666(8) Å, and Z=4; R=0.0327, wR=0.085. The crystal structure consists of infinite zigzag one-dimensional chains of 2-(2-ammoniumethyl)-1-méthyl pyrrolidinium dications and distorted [CuCl₄]^2? tetrahedral anions along the b axis. The cohesion of the atomic arrangement is ensured by hydrogen bonding (N–H?Cl). The temperature dependence of the magnetic susceptibility was measured in the temperature range of 2–100 K at different magnetic field intensities. The results indicate that the complex exhibit a weak antiferromagnetic coupling between the copper (II) centers. The ferromagnetic ordering is further confirmed by the magnetic field dependence of the magnetization between 2 and 30 K.     

Soft mechanochemical synthesis of MgFe2O4 nanoparticles from the mixture of α-Fe2O3 with Mg(OH)2 and Fe(OH)3 with Mg(OH)2

Abstract

The influence of long term soft milling of a mixture of (1) Mg(OH)₂ and α-Fe₂O₃ and (2) Mg(OH)₂ and Fe(OH)₃ powders in a planetary ball mill on the reaction synthesis of nanosized MgFe₂O₄ ferrites was studied. Soft mechanochemical reaction leading to formation of the MgFe₂O₄ spinel phase was followed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and magnetisation measurements. The spinel phase formation was first observed after 5 h of milling and its formation was completed after 15 h in case (2). The synthesised MgFe₂O₄ ferrite had a nanocrystalline structure with a crystallite size of about 10 and 15 nm respectively for cases (1) and (2). Measurements after 15 h of milling show magnetisation values of 15·23 and 10·14 J T^–1 kg^–1 respectively for cases (1) and (2).     

Sintering and crystallization of (SrO·SiO2)-(SrO·Al2O3·2SiO2) glass-ceramics

In the ternary SrO-Al₂O₃-SiO₂ system the pseudobinary join composition of 50 wt % SrO·SiO₂–50 wt % SrO·Al₂O₃·2SiO₂ (SS-SA2S) showed a glass melting temperature of 1500 °C and a crystallization peak temperature of 1100 °C. The (SS-SA2S) glass-ceramic pellets prepared by cold pressing and pressureless sintering, showed very low porosity. The (SS-SA2S) glass-ceramics containing B₂O₃ and those containing B₂O₃ and TiO₂ revealed crystallization peak temperatures of 1000 °C and unexpectedly high porosity. By applying Kissinger analyses to the DTA data the activation energy values for crystallization of the three glass-ceramics were determined to range from 196 to 255 kJ/mol. The Ozawa analyses on the DTA data gave the Avrami parameter values at 3.69 to 3.95. The X-ray diffraction (XRD) patterns from the three glass-ceramics revealed formation of the equilibrium crystalline phases of SrO·SiO₂ and SrO·Al₂O₃·2SiO₂ (monocelsian).     

Cobalt-mediated synthesis of 2-(4-pyridyl)benzimidazole. x-ray structures of Co[2-(4-pyridyl)benzimidazole]2(H2O)2(NO3)2 and [Co(isonicotinate)(4-pyridiniumcarboxylate)(H2O)(NO3)]∞

We have observed an unusual example of cobalt-mediated cyclization of 4-pyridinecarboxaldehyde and 2-nitroaniline to afford 2-(4-pyridyl)benzimidazole under hydro(solvo)thermal conditions. Reaction of Co(NO₃)₂·6H₂O with 4-pyridinecarboxaldehyde and 2-nitroaniline in ethanol at 120°C gave a cobalt(II) coordination compound, Co[2-(4-pyridyl)benzimidazole]₂(H₂O)₂(NO₃)₂, 1. In contrast, when the hydro(solvo)thermal reaction was carried out between Co(NO₃)₂·6H₂O and isonicotinic acid in the presence of 2-nitroaniline at 110°C, a one-dimensional Co(II) coordination polymer with the formula of [Co(isonicotinate)(4-pyridiniumcarboxylate)(H₂O)(NO₃)]_∞, 2, resulted. The X-ray single crystal structures of both 1 and 2 are described. Interestingly, the isonicotinic acid in 2 exists as a 4-pyridiniumcarboxylate tautomer, and the pyridinium hydrogen atom forms a very strong hydrogen bond to the carboxylate oxygen of the 4-pyridiniumcarboxylate on an adjacent metal center. 1 forms a three-dimensional polymeric network through hydrogen bonding interactions, while 2 exists as a 2-D bilayer polymeric network through hydrogen bonding interactions.     

Synthesis and Characterization of Sm_xGd_yCe_(1-x-y)O_(2-δ) Nanopowders

SmxGdyCe1-x-yO2-δ (x+y=0.2 and x=0, 0.04, 0.08, 0.12, 0.16, 0.2) nanopowders were prepared by a copre-cipitation method. The zeta potential and sedimentation volume of Ce(OH)4 aqueous dispersions at different pH values were measured. The isoelectric point (IEP) of Ce(OH)4 suspensions is 7.0. The maximum potential value of -18.5 mV and maximum sedimentation volume of 19 ml are reached at pH=10. The evolution behaviors of the xSm(OH)3·yGd(OH)3·(1-x-y)Ce(OH)4 dried powders in the heating process was characterized by DTA/TG and XRO. The powders decompose to ceria based solid solution at a temperature below 300℃ and forms cubic fluorite structure ceria at about 650℃. The properties of SmxGdyCe1-x-yO2-δ solid solutions were characterized by XRD, TEM and BET. The lattice parameter of doped Ce02 increases linearly with increasing Sm3+ substitution (or decreasing Gd3+ substitution). The particle size of the doped ceria powders is from 5 nm to 10 nm.     

One-step solid state synthesis of capped γ-Fe(2)O(3) nanocrystallites

The thermally induced solid state synthesis of soluble organophilic maghemite (γ-Fe(2)O(3)) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt state of Fe(NO)(3)·9H(2)O and RCOOH (R = C(11)H(23), C(15)H(31)) at 240?°C. The method yields well-crystallized nanoparticles of γ-Fe(2)O(3) functionalized with the corresponding aliphatic acid. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations reveal composite particles with faceted magnetic cores and average size of 20?nm, which are well capped with the surrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermal analysis suggest a bimodal configuration of the organic shell including chemically coordinated and physisorbed molecules of aliphatic acid. The chemical bonding of the carboxylate groups to the surface iron atoms is also indicated by a paramagnetic doublet with unchanged area in the variable temperature M?ssbauer spectra. The spinel γ-Fe(2)O(3) particles exhibit perfect structural and magnetic ordering, including the almost ideal ratio of octahedral to tetrahedral positions (5/3) and very low degree of spin canting, as confirmed by in-field M?ssbauer spectroscopy. Magnetic measurements demonstrate the suitable properties required in various (bio)magnetic applications like superparamagnetic behavior at room temperature, high saturation magnetization achievable at low applied fields and suppressed magnetic interactions.