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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Mononuclear gallium complexes with the redox-active dmp-bian ligand (dmp-bian is 1,2-bis[(2,6-dimethylphenyl)imino]acenaphthene): synthesis and reactions with alkynes

The direct reduction of 1,2-bis[(2,6-dimethylphenyl)imino]acenaphthene (dmp-bian (1)) with gallium metal in toluene affords the solvent-free bis-ligand complex [(dmp-bian){sub 2}Ga] (2), in which two diimine ligands are in different oxidation states (radical-anionic and dianionic). The addition of phenylacethylene to the Ga–N–C moiety of the dianionic ligand of compound 2 gives the complex [(dmp-bian)Ga(HC=CPh)(dmp-bian)] (3), in which new Ga–C and C–C bonds are formed. The reaction of 2 with hex-1-yne produces the gallium dialkynyl complex [(dmp-bian)Ga(C≡C–Bu){sub 2}] (4), with the metal atom bonded to the dmp-bian radical anion. Paramagnetic compounds 2–4 were characterized by ESR spectroscopy and X-ray diffraction. The known compound dmp-bian was structurally characterized for the first time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Spin transition characteristics of molecular solvates of Cu{sup II} complexes with nitroxides: sensitivity to the packing type

A method for the synthesis of solvates of dinuclear heterospin complexes of bis(hexafluoroacetylacetonato)copper(II) with 2-(4-methylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L{sup Me}) and 2-(4-ethylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L{sup Et}) of the composition [Cu(hfac){sub 2}L{sup R}]{sub 2} · Solv (Solv = benzene, bromobenzene, toluene, o-xylene, p-xylene) was developed. It was found that a decrease in temperature induces structural transformations of the solid phases of the complexes followed by significant changes in the distances between the paramagnetic centers in the intramolecular exchange clusters {Cu"2"+-O"·-} from 2.321 to 1.974 Å. As a result, the temperature dependences of the effective magnetic moment μ{sub eff}(T) exhibit magnetic features similar to spin transitions. An analysis of the shape of the μ{sub eff}(T) curves suggested that the magnetic properties of the compounds under study depend primarily on the molecular packing. A comparison of the magneto-structural correlations typical of the [Cu(hfac){sub 2}L{sup R}]{sub 2} · Solv complexes studied in this work with the data obtained earlier for analogous solvates of heterospin polymer chain complexes showed that the spin transition characteristics of the [Cu(hfac){sub 2}L{sup R}]{sub 2} · Solv systems are much less sensitive to the change of the solvent than the corresponding characteristics of the heterospin polymers containing solvate molecules in the interchain space. The magnetic characteristics of the heterospin dimer molecules depend primarily on which cavity between the dimers is filled with solvate molecules. For solvates with monoclinic symmetry, changes in the solvent molecules occupying same-type cavities have almost no effect on the spin transition characteristics in the heterospin exchange cluster.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Influence of Dynamic Three Point Bending on the Work Hardening Capacity of T105Mn120 Manganese Steel

The paper analyzes work hardening behavior of T105Mn120 Hadfield steel under dynamic conditions. The specimens were investigated under two states: (a) untreated (as cast) and (b) solution treated to 1100 °C. Dynamic flexural behavior was examined by means of three-point-bending tests performed with a dynamic mechanical analyser (DMA), and structural analysis was done by x-ray diffraction, optical and scanning electron microscopy; DMA tests were performed under two variants: (a) temperature scans, between − 150 and 400 °C and (b) isothermal strain sweeps, up to 0.15% strain amplitudes. The former emphasized the critical temperatures of thermally induced reversible martensitic transformation and antiferromagnetic–paramagnetic phase transition, while the latter enabled to monitor the storage modulus increase due to the work hardening caused by dynamic bending. Strain sweeps tests revealed the effects of both dynamic bending frequency and number of cycles. The largest work hardening effect, obtained after five strain sweep cycles applied at the frequency of 5 Hz, was associated with the finest distribution of precipitated carbides, observed by differential scanning calorimetry and the formation of slip micro-bands, illustrated on OM micrographs and SEM energy dispersion spectroscopy maps.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evaluation of the Microstructure and Performance of Fe-21Cr-15Ni-6Mn-Nb Nonmagnetic Stainless Steel Welded Joints

In the present study, double-sided gas shield welding (GSW), in a single pass, was applied to Fe-21Cr-15Ni-6Mn-Nb nonmagnetic stainless steel plate. The microstructure and performance of the welded joint were investigated via microstructural and phase analysis, mechanical testing and magnetic analysis. The results showed a satisfactory micrographic appearance with full penetration, and no solidification defects observed in the welded joint, which showed typical epitaxial growth characteristics in the welding solidification. Slight grain growth, with an average size of ~ 18.9 μm, occurred in the heat-affected zone (HAZ). The primary dendrite arms, on both sides of welding joint, grew along the direction of the temperature gradient and met at the centerline of the weld with no parting microstructure in evidence. The secondary dendrite arm spacing was stable in all parts of the weld zone (WZ). The hardness of the weld zone was higher than that of the HAZ and the base metal (BM), with the lowest hardness occurring in the HAZ. The results of tensile testing showed a higher strength of the welded metal (WM) compared to the BM, and a good strength-ductility balance of the welded joint. The impact energy of the HAZ was higher than that of the WZ, corresponding to 60.5 J at room temperature and 52.7 J at − 196 °C. Microvoid coalescence, concurrent with crack propagation along the direction of the long axis of the dendritic sub-grains, was observed during plastic deformation in the WZ. Additionally, the excellent paramagnetic characteristics of the welded specimens were revealed.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Quantum critical behavior in three-dimensional one-band Hubbard model at half-filling

A one-band Hubbard model with hopping parameter t and Coulomb repulsion U is considered at half-filling. By means of the Schwinger bosons and slave fermions representation of the electron operators and integrating out the spin–singlet Fermi fields an effective Heisenberg model with antiferromagnetic exchange constant is obtained for vectors which identifies the local orientation of the spin of the itinerant electrons. The amplitude of the spin vectors is an effective spin of the itinerant electrons accounting for the fact that some sites, in the ground state, are doubly occupied or empty. Accounting adequately for the magnon–magnon interaction the Néel temperature is calculated. When the ratio t/U is small enough (t/U ≤0.09) the effective model describes a system of localized electrons. Increasing the ratio increases the density of doubly occupied states which in turn decreases the effective spin and Néel temperature. The phase diagram in the plane of temperature (T{sub N})/U and parameter t/U is presented. The quantum critical point (T{sub N}=0) is reached at t/U =0.9. The magnons in the paramagnetic phase are studied and the contribution of the magnons’ fluctuations to the heat capacity is calculated. At the Néel temperature the heat capacity has a peak which is suppressed when the system approaches a quantum critical point. It is important to stress that, at half-filling, the ground state, determined by fermions, is antiferromagnetic. The magnon fluctuations drive the system to quantum criticality and when the effective spin is critically small these fluctuations suppress the magnetic order. -- Highlights: •Technique of calculation is introduced which permits us to study the magnons’ fluctuations. •Quantum critical point is obtained in the one-band 3D Hubbard model at half-filling. •The present analytical results supplement the numerical ones (see Fig. 7)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Localization of disordered bosons and magnets in random fields

We study localization properties of disordered bosons and spins in random fields at zero temperature. We focus on two representatives of different symmetry classes, hard-core bosons (XY magnets) and Ising magnets in random transverse fields, and contrast their physical properties. We describe localization properties using a locator expansion on general lattices. For 1d Ising chains, we find non-analytic behavior of the localization length as a function of energy at ω=0, ξ{sup −1}(ω)=ξ{sup −1}(0)+A|ω|{sup α}, with α vanishing at criticality. This contrasts with the much smoother behavior predicted for XY magnets. We use these results to approach the ordering transition on Bethe lattices of large connectivity K, which mimic the limit of high dimensionality. In both models, in the paramagnetic phase with uniform disorder, the localization length is found to have a local maximum at ω=0. For the Ising model, we find activated scaling at the phase transition, in agreement with infinite randomness studies. In the Ising model long range order is found to arise due to a delocalization and condensation initiated at ω=0, without a closing mobility gap. We find that Ising systems establish order on much sparser (fractal) subgraphs than XY models. Possible implications of these results for finite-dimensional systems are discussed. -- Highlights: •Study of localization properties of disordered bosons and spins in random fields. •Comparison between XY magnets (hard-core bosons) and Ising magnets. •Analysis of the nature of the magnetic transition in strong quenched disorder. •Ising magnets: activated scaling, no closing mobility gap at the transition. •Ising order emerges on sparser (fractal) support than XY order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Raman scattering of photons by hydrogenlike ions I: A semirelativistic and nondipole approach

Going beyond the usual nonrelativistic treatments of Raman scattering of light by a ground-state electron in hydrogenic ions, we propose in this work a semirelativistic and nondipole approach in the case of inelastic process under the ionization threshold. This scheme is based, on the one hand, on the discrete semirelativistic Coulomb Sturmian basis sets, and on the other hand, on the direct Foldy–Wouthuysen interaction Hamiltonian derived recently from the Dirac equation with electromagnetic potentials (Hinschberger and Hervieux 2012) and confirmed by us to seventh order in powers of 1∕m. It includes the paramagnetic, the diamagnetic, the magnetic field–spin and the electric field–spin interactions. Moreover, the photon fields are expanded in electric and magnetic multipoles and nondipole effects are fully taken into account. On utilizing these ingredients, we build in detail the multipole expansion of the semirelativistic Raman scattering cross section when the photon energy is under the ionization threshold. For each type of the allowed multipole components, namely EE, MM and EM in the standard notations, suitable closed forms of total scattering cross sections are calculated for numerical computations. Such analytical expressions enable the evaluation of the contribution of each of these interaction operators and field multipoles in the scattering process.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Synergistic enhancement of iron oxide nanoparticle and gadolinium for dual-contrast MRI

Highlights: Black-Right-Pointing-Pointer MR contrast agents exert influence on T{sub 1} or T{sub 2} relaxation time of the surrounding tissue. Black-Right-Pointing-Pointer Combined use of iron oxide and Gd-DTPA can improve the sensitivity/specificity of lesion detection. Black-Right-Pointing-Pointer Dual contrast MRI enhances the delineation of tumor borders and small lesions. Black-Right-Pointing-Pointer The effect of DC-MRI can come from the high paramagnetic susceptibility of Gd{sup 3+}. Black-Right-Pointing-Pointer The effect of DC-MRI can also come from the distinct pharmacokinetic distribution of SPIO and Gd-DTPA. -- Abstract: Purpose: The use of MR contrast agents allows accurate diagnosis by exerting an influence on the longitudinal (T{sub 1}) or transverse (T{sub 2}) relaxation time of the surrounding tissue. In this study, we combined the use of iron oxide (IO) particles and nonspecific extracellular gadolinium chelate (Gd) in order to further improve the sensitivity and specificity of lesion detection. Procedures: With a 7-Tesla scanner, pre-contrasted, IO-enhanced and dual contrast agent enhanced MRIs were performed in phantom, normal animals, and animal models of lymph node tumor metastases and orthotopic brain tumor. For the dual-contrast (DC) MRI, we focused on the evaluation of T{sub 2} weighted DC MRI with IO administered first, then followed by the injection of a bolus of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). Results: Based on the C/N ratios and MRI relaxometry, the synergistic effect of coordinated administration of Gd-DTPA and IO was observed and confirmed in phantom, normal liver and tumor models. At 30 min after administration of Feridex, Gd-DTPA further decreased T{sub 2} relaxation in liver immediately after the injection. Additional administration of Gd-DTPA also immediately increased the signal contrast between tumor and brain parenchyma and maximized the C/N ratio to -4.12 {+-} 0.71. Dual contrast MRI also enhanced the delineation of tumor borders and small lesions. Conclusions: DC-MRI will be helpful to improve diagnostic accuracy and decrease the threshold size for lesion detection.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Biophysical characterization of the structural change of Nopp140, an intrinsically disordered protein, in the interaction with CK2α

Nucleolar phosphoprotein 140 (Nopp140) is a nucleolar protein, more than 80% of which is disordered. Previous studies have shown that the C-terminal region of Nopp140 (residues 568–596) interacts with protein kinase CK2α, and inhibits the catalytic activity of CK2. Although the region of Nopp140 responsible for the interaction with CK2α was identified, the structural features and the effect of this interaction on the structure of Nopp140 have not been defined due to the difficulty of structural characterization of disordered protein. In this study, the disordered feature of Nopp140 and the effect of CK2α on the structure of Nopp140 were examined using single-molecule fluorescence resonance energy transfer (smFRET) and electron paramagnetic resonance (EPR). The interaction with CK2α was increased conformational rigidity of the CK2α-interacting region of Nopp140 (Nopp140C), suggesting that the disordered and flexible conformation of Nopp140C became more rigid conformation as it binds to CK2α. In addition, site specific spin labeling and EPR analysis confirmed that the residues 574–589 of Nopp140 are critical for binding to CK2α. Similar technical approaches can be applied to analyze the conformational changes in other IDPs during their interactions with binding partners. - Highlights: • Nopp140 is intrinsically disordered protein (IDP). • Conformation of Nopp140 became more rigid conformation due to interaction with CK2α. • smFRET and EPR could be applied to analyze the structural changes of IDPs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Spectroscopic investigation of historical uranium glasses

Here, we present spectroscopic investigations of uranium in two historical glasses. A 1920's-1930's Art Deco (Bagley Carnival) green soda-lime-silica uranium glass bowl and a 1930's-1940's (Thomas Webb) yellow full lead crystal uranium glass vase were studied using optical absorption spectroscopy, XRF and SEM-EDX, X-band EPR and High- Energy Resolution Fluorescence-Detected (HERFD)-XANES. Uranium speciation may be different in the two glasses. Uranium occurs as uranyl groups (UO 2 2+ ) with minority reduced uranium species, mostly as U(V), more important in the Webb glass than in the Bagley glass. The differences between the two glasses arise from the fining procedure and result from the presence of other multivalent elements and differences in base glass composition. Electron Paramagnetic Resonance (EPR) spectra show the presence of an incipient signal close to g~2, partially annealed by heating to 550 °C, which we assign to a small concentration of radiation-induced defects caused by uranium decay. The presence of multivalent glass components in addition to U (As + Cu + Fe in the Bagley glass and Sb + Fe in the Webb glass) can trap the electron-hole pairs generated by the presence of uranium. This may explain the weakness of this signal in these glasses that anyway received a limited radiation dose since their fabrication. The low activity of these glasses, close to the background radiation, confirms that there is no danger to exhibiting them in museums.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Comparison of Nodal Risk Formula and MR Lymphography for Predicting Lymph Node Involvement in Prostate Cancer

Purpose: To compare the nodal risk formula (NRF) as a predictor for lymph node (LN) metastasis in patients with prostate cancer with magnetic resonance lymphography (MRL) using Ultrasmall Super-Paramagnetic particles of Iron Oxide (USPIO) and with histology as gold standard. Methods and Materials: Logistic regression analysis was performed with the results of histopathological evaluation of the LN as dependent variable and the nodal risk according to the NRF and the result of MRL as independent input variables. Receiver operating characteristic (ROC) analysis was performed to assess the performance of the models. Results: The analysis included 375 patients. In the single-predictor regression models, the NRF and MRL results were both significantly (p <0.001) predictive of the presence of LN metastasis. In the models with both predictors included, NRF was nonsignificant (p = 0.126), but MRL remained significant (p <0.001). For NRF, sensitivity was 0.79 and specificity was 0.38; for MRL, sensitivity was 0.82 and specificity was 0.93. After a negative MRL result, the probability of LN metastasis is 4% regardless of the NRF result. After a positive MRL, the probability of having LN metastasis is 68%. Conclusions: MRL is a better predictor of the presence of LN metastasis than NRF. Using only the NRF can lead to a significant overtreatment on the pelvic LN by radiation therapy. When the MRL result is available, the NRF is no longer of added value.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2025

Structural basis of heme scavenging by the ChtA and HtaA hemophores in Corynebacterium diphtheriae

Corynebacterium diphtheriae causes diphtheria, a potentially fatal infectious disease that damages tissues in the upper respiratory tract. In order to proliferate, this pathogen acquires the essential nutrient iron from heme (iron-protoporphyrin IX) primarily found in human hemoglobin (Hb). C. diphtheriae secretes ChtA and HtaA hemophore proteins that bind ferric heme (hemin) via conserved region (CR) domains. Here, we demonstrate that their CR domains scavenge hemin after it is spontaneously released from Hb, and define the structural basis of hemin binding to ChtA and the N-terminal CR domain from HtaA by determining X-ray crystal structures of their protein-hemin complexes. Resonance Raman and electron paramagnetic resonance experiments demonstrate that the CR domains from ChtA and HtaA engage in pentacoordinate hemin binding through a conserved iron-tyrosyl linkage, though variations in their hemin pockets alter the way they stabilize the axial tyrosine and mask hemin’s metal. The importance of these interactions is probed using isothermal titration calorimetry experiments, which represent the first quantitative assessment of CR-hemin affinity and reveal that ChtA binds hemin via an enthalpically driven process. Hemin partitioning experiments using native mass spectrometry demonstrate that the cohort of CR domains within C. diphtheriae ’s hemin-uptake system have dissociation constants for hemin between 0.8 and 22 nM, raising the possibility that affinity differences contribute to the directional flow of hemin into the cell. Collectively, the results of this work provide insight into how C. diphtheriae and other pathogenic and commensal corynebacterium species utilize CR domains to scavenge iron rich hemin from their environment.

Corynebacterium diphtheriae↗
DOE OSTI2013

Structure-Activity Relationships in NH3-SCR over Cu-SSZ-13 as Probed by Reaction Kinetics and EPR Studies

Cu-SSZ-13 catalysts with various Cu loadings were prepared via solution ion exchange. The hydrated samples were studied with Electron Paramagnetic Resonance (EPR). Cu2+ ion coordination numbers were obtained by analyzing the hyperfine structures while Cu-Cu distances were estimated from line broadening of the EPR features. By coupling EPR and temperature-programmed reduction (TPR) results, two Cu2+ ion locations were suggested. Standard and fast NH3-SCR, as well as non-selective NH3 oxidation reactions were carried out over these catalysts at high space velocities. For the SCR reaction, intra-particle diffusion limitation was found throughout the reaction temperatures investigated. Although clear structure-activity relationships cannot be derived, the reaction results allow for reactant diffusivities and Cu2+ ion locations to be estimated. The slower NH3 oxidation reaction, on the other hand, is kinetically limited at low temperatures, and, therefore, allows for a correlation between Cu2+ ion location and reaction kinetics to be made. Furthermore, the dynamic Cu2+ ion motion as a function of temperature could also be derived from the NH3 oxidation kinetics.

Cu-SSZ-13↗
DOE OSTI2019

Effect of X-ray beam on the molecular–topological structure of the surface of kynar® polyvinylidene fluoride resin

Thermomechanical analysis of poly(vinylidene fluoride) (PVDF) film shows that, unlike the completely amorphous structure of the native polymer, after irradiation with X-rays, the weight fraction of the crystalline modification in the polymer is 0.5. The initial PVDF film had a linear thermal expansion coefficient of α 1 = 11.33х10 5 K -1 and a glass transition temperature of T g =256 K. An efficient conversion of the amorphous structures of the polymer pseudo-network into crystalline networks occurs under X-ray irradiation. The irradiated polymer exhibits amorphous ( T g =239 K) and crystalline topological blocks ( T m =385 K). The presence of polyenyl and alkyl radicals is found in the electron paramagnetic resonance (EPR) spectra of the irradiated polymer. Lines with a splitting of 3.3 m T can be observed at the edges of the EPR spectra, consistent with radical centers like -CF 2 -C • H-CF 2 - . At high doses of radiolysis, polyenyl radicals are the main observed radicals. The macromolecular chains contain all three (α, β, γ) morphologies of the polymer. The Raman spectra show that X-ray irradiation can lead to carbonization and the formation of unsaturated bonds. Electronic structure calculations were used to aid in the analysis of the observed spectra.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Terahertz EPR spectroscopy using a 36-tesla high-homogeneity series-connected hybrid magnet

Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as Mn II (3d 5 ) or Gd III (4f 7 ), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive “Keck” magnet at the NHMFL. Herein, we report the first EPR experiments performed using the SCH magnet capable of reaching the field of 36 T, corresponding to an EPR frequency of 1 THz for g = 2. The magnet’s intrinsic homogeneity (25 ppm, that is 0.9 mT at 36 T over 1 cm diameter, 1 cm length cylinder) was previously established by NMR. We characterized the magnet’s temporal stability (5 ppm, which is 0.2 mT at 36 T over one-minute, the typical acquisition time) using 2,2-diphenyl-1-picrylhydrazyl (DPPH). This high resolution enables resolving the weak g-anisotropy of 1,3-bis(diphenylene)-2-phenylallyl (BDPA), Δg = 2.5 × 10 –4 obtained from measurements at 932 GHz and 33 T. Subsequently, we recorded EPR spectra at multiple frequencies for two Gd III complexes with potential applications as spin labels. In conclusion, we demonstrated a significant reduction in line broadening in Gd[DTPA], attributed to second order zero field splitting, and a resolution enhancement of g-tensor anisotropy for Gd[sTPATCN]-SL.

47 OTHER INSTRUMENTATION↗
DOE OSTI2011

Structure and properties of a novel cobaltate La{sub 0.30}CoO{sub 2}

The layered cobaltate La{sub 0.30}CoO{sub 2} was prepared from Na{sub x}CoO{sub 2} precursor by a solid-state ionic exchange and was characterized by means of X-ray and neutron diffraction, magnetic, thermal and electric transport measurements. The compound consists of hexagonal sheets of edge-sharing CoO{sub 6} octahedra interleaved by lanthanum monolayers. Compared to Na{sup +} in the parent system, the La{sup 3+} ions occupy only one-third of available sites, forming a 2-dimensional superstructure. The deviation from the ideal stoichiometry La{sub 1/3}CoO{sub 2} introduces extra hole carriers into the diamagnetic LS Co{sup 3+} matrix making the sample Pauli paramagnetic. The temperature dependence of the electrical conductivity in La{sub 0.30}CoO{sub 2} follows Mott's T{sup -1/3} law up to about 400 K, which is in contrast with the standard metallic behavior in the Na{sup +} homolog possessing the same formal doping. The experiments are complemented by electronic structure calculations for La{sub 0.30}CoO{sub 2} and related Na{sub x}CoO{sub 2} systems. - Graphical abstract: Optimized superstructure of La{sub 0.3}CoO{sub 2} obtained by LDA calculation. Highlights: > A novel layered cobaltate La{sub 0.30}CoO{sub 2} was prepared by a solid-state ionic exchange. > La{sup 3+} ions are ordered and form a 2-dimensional superstructure. > Electrical conductivity of variable range hopping type up to 400 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Crystallographic and magnetic properties of (Cu{sub 1-x}V{sub x})V{sub 2}S{sub 4} (x{approx}0.3) single crystals with the layered defect NiAs structure synthesized under high pressure

We report on the reproducible growth of (Cu{sub 1-x}V{sub x})V{sub 2}S{sub 4} single crystals of sizable dimensions ({approx}0.3 mm) and homogeneous composition (x{approx}0.3) by means of high-pressure synthesis. The refinement of single crystal X-ray diffraction data indicates that the crystal structure is of the monoclinic defect NiAs-type, which consists of a stacking of VS{sub 2} layers with CdI{sub 2}-type structure and chains of edge-sharing (Cu{sub 1-x}V{sub x})S{sub 6} octahedra. Layers and chains form a network of face-sharing octahedra with no Cu-V intra-chain ordering. A combined X-ray photoelectron spectroscopy and bond valence sum analysis indicates that the valence of the V and Cu ions are 3+ and 1+, respectively. Magnetic susceptibility measurements unveil the coexistence of a large Pauli-like and of a small Curie-like paramagnetic contributions, with no evidence of any long range order down to 2 K. This result suggests a picture of predominantly itinerant 3d V electrons with significant electron-electron correlations. - Graphical Abstract: Crystallographic structure of (Cu{sub 0.69}V{sub 0.31})V{sub 2}S{sub 4}. For clarity, the octahedral environment of (Cu{sub 0.69}V{sub 0.31}) site is not shown. Highlights: > Synthesis of new single-crystals in the Cu-V-S system using high pressure and high temperature. > Structural analysis revealed the single-crystals to be of the defect NiAs-type structure. > Bond valence sum analysis combined to X-ray photoemission spectroscopy revealed Cu{sup 1+} and a majority of V{sup 3+}. > Magnetic susceptibility has been measured. > Charge carriers are of two types, localized and itinerant.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗