High Field X-ray Diffraction Research Articles

Dendrimer-encapsulated PtSn bimetallic ultrafine nanoparticles supported on graphitic mesoporous carbon as efficient electrocatalysts for methanol oxidation

Catalytic performance of Pt based nanocatalysts significantly depends on their morphologies, compositions and structures. In this work, the generation-4 phenylazomethine-tetraphenylmethane dendrimer (TPMG4)-encapsulated PtSn bimetallic ultrafine nanoparticles with tunable ratio of Pt and Sn (PtnSn60-n@TPMG4/GMC, n = 56, 48, 32) supported on graphitic mesoporous carbon (GMC) were fabricated through co-reduction method by using the phenylazomethine dendrimer as a template. The morphologies, compositions, and structures of resulting PtnSn60-n@TPMG4/GMC were detected by UV–vis absorption spectra (UV–vis), inductively coupled plasma-optical emission spectroscopy (ICP-OES), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements. These physical characterizations show that dendrimer-encapsulated PtnSn60-n nanoparticles are anchored on the surface of graphitic mesoporous carbon with highly dispersion and uniformly ultrafine size of ∼1 nm, The atomic ratio of Pt and Sn in PtnSn60-n bimetallic nanoparticles can be accurately controlled. The electrochemical characterizations demonstrate that all PtnSn60-n@TPMG4/GMC samples exhibit more excellent electrocatalytic performance for methanol oxidation than single metal Ptm@TPMG4/GMC and commercial carbon supported platinum catalyst (Pt/C). Especially, the Pt56Sn4@TPMG4/GMC displays the highest catalytic activity with 1.6 times higher than Pt60/GMC and 1.9 times higher than Pt/C. Also, the Pt56Sn4@TPMG4/GMC exhibits the high carbon monoxide (CO) tolerance and superior catalytic stability towards methanol oxidation. Consequently, constructing Pt based bimetallic nanoparticles with controllable compositions and structures is an effective way to improve the catalytic performance and reduce the amount of Pt used in the catalysts, which will be widely concerned in the field of direct methanol fuel cells.

Nanocrystalline silver coatings on steel by electrodeposition from non-polluting aqueous baths and its antibacterial activity

BackgroundAntimicrobial coatings are one way that could help inhibit the spread of germs. Despite significant research into a variety of antimicrobial coatings with varied formulas, silver-based coatings appear to be the most effective. Electrodeposition is a promising technology to synthesize nanocrystalline silver coatings which have a wide range of applications such as in microelectronics, aerospace, automotive, biotechnology, nanobiotechnology, bioengineering sciences, in addition to its antimicrobial characteristics. Regrettably, cyanide electrolyte which is commonly applied in industry for silver coatings is one of the most hazardous substances, raising serious health and environmental hazards. It is important that seek high environmentally friendly electrolytes alternative to cyanide electrolytes. MethodsThe nanocrystalline silver coatings were successfully synthesized via galvanostatic deposition on stainless steel surface from an environmentally friendly novel bath. The electrochemical measurements were made utilizing linear sweep voltammetry (LCV), and cyclic voltammetry (CV). A high field emission scanning electron microscope (FESEM) and X-ray diffraction analysis (XRD) were used to characterize the obtained silver coatings. Significant findingsBright and adherent nanocrystalline Ag coatings (nano-size ranging between 14.8 and 67.6 nm) were synthesized by direct galvanostatic electrodeposition on SS surface from a bath free from cyanide. This environmentally friendly, cyanide-free bath is characterized by its high stability, low cost, and high cathodic current efficiency. The morphology was strongly dependent on the electrolyte composition as well as on the run circumstances. The microhardness of Ag deposited from this bath has a relatively high value (120.2–158.7 kg f mm-2) depending on the applied current density. Furthermore, the nanocrystalline silver coatings formed by these baths are excellent antibacterial agents versus a vast spectrum of gram-positive and gram-negative bacteria, particularly Listeria and Streptococcus bacteria.

High magnetic field x-ray diffraction study of the α phase of solid oxygen: Absence of giant magnetostriction

High magnetic field x-ray diffraction experiments of solid oxygen have been performed at 10 K using DC magnetic fields of up to 5 T as well as pulsed magnetic fields of up to 25 T. The $\ensuremath{\alpha}$ phase of oxygen exhibits no magnetostriction greater than $\mathrm{\ensuremath{\Delta}}d/d={10}^{\ensuremath{-}4}$ at 5 T, where $d$ and $\mathrm{\ensuremath{\Delta}}d$ denote a lattice plane spacing and its magnetic field variation, respectively. The $\mathrm{\ensuremath{\Delta}}d/d$ at higher fields of up to 25 T is found to be smaller than $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. These results contradict the previously reported giant magnetostriction in the $\ensuremath{\alpha}$ phase where the volume magnetostriction $\mathrm{\ensuremath{\Delta}}V/V$ reaches ${10}^{\ensuremath{-}2}$ at 7.5 T [K. Katsumata et al., J. Phys.: Condens. Matter 17, L235 (2005)].

Combining solid state NMR, powder X-ray diffraction, and DFT calculations for CsSc3F10 structure determination

A combination of high field solid-state MAS NMR spectroscopy, X-ray diffraction, and first-principles calculations is used to elucidate the crystalline structure of CsSc3F10. At room temperature, this phase was found to crystallize in the Pmma (n°51) space group with a = 8.0837(1) Å, b = 7.5764(1) Å, and c = 6.8127(1) Å. The remarkable feature of CsSc3F10 is an unusual high cesium coordination number of 18. 45Sc -19F D-HMQC NMR method has been employed to investigate the connectivity of scandium with fluorine atoms. NMR parameters were determined using first principle DFT calculations and compared with experimentally obtained data.

High Field X-ray Diffraction Study for Ni46.4Mn38.8In12.8Co2.0 Metamagnetic Shape Memory Film

The transformation behaviors on metamagnetic shape memory Ni46.4Mn38.8In12.8Co2.0 film were investigated by X-ray diffraction experiments in the temperature up to 473 K and magnetic fields µ0H up to 5 T. The prepared film showed the parent phase with L21 structure at 473 K, and with preferred orientation along the 111 plane. The magnetic field induced reverse transformation was directly observed at T = 366 K, which was just around the reverse transformation starting temperature.

Strong visible and near infrared photoluminescence from ZnO nanorods/nanowires grown on single layer graphene studied using sub-band gap excitation

Fabrication and optoelectronic applications of graphene based hybrid 2D-1D semiconductor nanostructures have gained tremendous research interest in recent times. Herein, we present a systematic study on the origin and evolution of strong broad band visible and near infrared (NIR) photoluminescence (PL) from vertical ZnO nanorods (NRs) and nanowires (NWs) grown on single layer graphene using both above band gap and sub-band gap optical excitations. High resolution field emission scanning electron microscopy and X-ray diffraction studies are carried out to reveal the morphology and crystalline quality of as-grown and annealed ZnO NRs/NWs on graphene. Room temperature PL studies reveal that besides the UV and visible PL bands, a new near-infrared (NIR) PL emission band appears in the range between 815 nm and 886 nm (1.40–1.52 eV). X-ray photoelectron spectroscopy studies revealed excess oxygen content and unreacted metallic Zn in the as-grown ZnO nanostructures, owing to the low temperature growth by a physical vapor deposition method. Post-growth annealing at 700 °C in the Ar gas ambient results in the enhanced intensity of both visible and NIR PL bands. On the other hand, subsequent high vacuum annealing at 700 °C results in a drastic reduction in the visible PL band and complete suppression of the NIR PL band. PL decay dynamics of green emission in Ar annealed samples show tri-exponential decay on the nanosecond timescale including a very slow decay component (time constant ∼604.5 ns). Based on these results, the NIR PL band comprising two peaks centered at ∼820 nm and ∼860 nm is tentatively assigned to neutral and negatively charged oxygen interstitial (Oi) defects in ZnO, detected experimentally for the first time. The evidence for oxygen induced trap states on the ZnO NW surface is further substantiated by the slow photocurrent response of graphene-ZnO NRs/NWs. These results are important for tunable light emission, photodetection, and other cutting edge applications of graphene-ZnO based 2D-1D hybrid nanostructures.

Development of an x-ray diffraction camera used in magnetic fields up to 10 T

A high-field x-ray diffraction (HF-XRD) camera was developed to observe structural changes of magnetic materials in magnetic fields up to 10 T. The instrument mainly consists of a Debye-Scherrer-type camera with a diameter of 80.1 mm, a 10-T cryocooled superconducting magnet with a 100-mm room-temperature bore, an x-ray source, a power supply, and a chiller for the x-ray source. An x-ray detector (image plate) in the HF-XRD camera can be taken out and inserted into the magnet without changing the sample position. The performance of the instrument was tested by measuring the HF-XRD for silicon and ferromagnetic MnBi powders. A change of x-ray diffraction pattern was observed due to the magnetic orientation of MnBi, showing that the instrument is useful for studying field-induced orientation processes and structural properties of field-controlled materials.

Observation of Reverse Transformation in Metamagnetic Shape Memory Alloy Ni<SUB>40</SUB>Co<SUB>10</SUB>Mn<SUB>34</SUB>Al<SUB>16</SUB> by High-Field X-Ray Diffraction Measurements

The structural properties of metamagnetic shape memory alloy Ni40Co10Mn34Al16 were investigated by X-ray powder diffraction measurements in the temperature range from 283 to 473 K and magnetic fields up to 5 T. With increasing temperature from 283 K, the alloy undergoes the reverse martensitic transformation from the tetragonal L10-type structure with the lattice parameter at ¼ 0:3853 nm and ct ¼ 0:3299 nm into the B2-type cubic structure with the lattice parameter ac ¼ 0:2924 nm at As ¼ 383 K. At 408 K (>As), we directly observed the field-induced reverse martensitic transformation. [doi:10.2320/matertrans.M2010150]

X-ray powder diffraction camera for high-field experiments

We have designed a high-field X-ray diffraction (HF-XRD) camera which will be inserted into an experimental room temperature bore (100 mm) of a conventional solenoid-type cryocooled superconducting magnet (10T-CSM). Using the prototype camera that is same size of the HF-XRD camera, a XRD pattern of Si is taken at room temperature in a zero magnetic field. From the obtained results, the expected ability of the designed HF-XRD camera is presented.

Performance of a Furnace for the High-field X-ray Diffraction Measurements at High Temperatures

An X-ray powder diffraction system in high temperature and in high magnetic fields was developed, which was performed at temperature ranging from room temperature to 473 K in the magnetic fields up to 5 T. The temperature stability was within ±1 K for 8 hours. To examine the ability of the system, high field and high temperature X-ray diffraction measurements were carried out for a novel ferromagnetic shape alloy, Ni40Co10Mn34Al16. We observed a field-induced reverse transformation in the alloy.

X-ray diffraction measurements in high magnetic fields and at high temperatures

A system was developed measuring x-ray powder diffraction in high magnetic fields up to 5 T and at temperatures from 283 to 473 K. The stability of the temperature is within 1 K over 6 h. In order to examine the ability of the system, the high-field x-ray diffraction measurements were carried out for Si and a Ni-based ferromagnetic shape-memory alloy. The results show that the x-ray powder diffraction measurements in high magnetic fields and at high temperatures are useful for materials research.

Magnetic and structural phase transitions of MnBi under high magnetic fields

High-field x-ray diffraction and magnetization measurements and differential thermal analysis (DTA) were carried out for polycrystalline MnBi with an NiAs-type hexagonal structure to investigate its magnetic and structural phase transitions. The lattice parameter a rapidly decreases below the spin reorientation temperature TSR(=90 K) in a zero magnetic field. The parameter c decreases gradually with decreasing temperature and exhibits an anomaly in the vicinity of TSR. By applying a magnetic field of 5 T, the parameter a increases by ∼0.05% when T<TSR and varies smoothly when 8≤T≤300 K. DTA data show that the magnetic phase transition temperature from the ferromagnetic state to the paramagnetic state increases linearly at a rate of 2 KT−1 with increasing magnetic field up to 14 T.

High field X-ray diffraction studies on magnetic refrigerants

High field X-ray diffraction studies on magnetic refrigerants

High-field X-ray diffraction measurements of novel ferromagnetic shape-memory alloy Ni 50Mn 36Sn 14

In order to clarify the structural properties of a novel ferromagnetic shape-memory alloy Ni 50Mn 36Sn 14 in magnetic fields, we have carried out high-field X-ray powder diffraction measurements under magnetic fields up to 5 T in the wide temperature range from 8 to 300 K. In this work, we confirmed that magnetic field induces the reverse martensitic transformation in Ni 50Mn 36Sn 14 at the vicinity of 220 K.

High Field X-ray Diffraction Study on a Magnetic-Field-Induced Valence Transition in YbInCu4

We report the first high-field x-ray diffraction experiment using synchrotron x-rays and pulsed magnetic fields exceeding 30 T. Lattice deformation due to a magnetic-field-induced valence transition in YbInCu4 is studied. It has been found that the Bragg reflection profile at 32 K changes significantly at around 27 T due to the structural transition. In the vicinity of the transition field the low-field and the high-field phases are observed simultaneously as the two distinct Bragg reflection peaks: This is a direct evidence of the fact that the field-induced valence state transition is the first order phase transition. The field-dependence of the low-field-phase Bragg peak intensity is found to be scaled with the magnetization.

High-Field X-ray Diffraction Measurement of SmMn2Ge2

The high-field X-ray diffraction measurement of a re-entrant ferromagnet SmMn2Ge2 with a tetragonal structure was carried out. The unit cell volume contracts by approximately 0.3% in the antiferromagnetic (AFM) state, compared with that of the ferromagnetic (FM) state. In the AFM state, the structural distortion recovers due to a high magnetic field, accompanied by the metamagnetic transition from the AFM state to the forced FM state.

High-field X-ray diffraction and high-pressure magnetization measurements of the pseudobinary compound Ce(Fe 0.9Co 0.1) 2

The magnetic and structural properties of Ce(Fe 0.9Co 0.1) 2 with the C15 cubic Laves-phase structure have been studied by magnetization measurement in high magnetic fields under high pressures, and powder X-ray diffraction measurement in fields up to 5 T. The C15 cubic structure is distorted to rhombohedral symmetry accompanied with the magnetic phase transition from the ferromagnetic to the antiferromagnetic state, which recovered the C15 structure by applying the magnetic field. The antiferromagnetic phase is induced by the lattice contraction due to hydrostatic pressure. Obtained results suggest that the AFM correlation due to the Ce 4f–Fe 3d hybridization plays an important role on the structural and magnetic properties.

Application of a portable pulsed magnet to synchrotron radiation experiments

A very small capacitor bank and miniature pulsed magnets have been developed to perform high-field synchrotron radiation experiments. A 20 T pulsed field can be generated using an energy of 1 kJ with typical pulse duration about 1 ms . Electron spin resonance experiments in millimeter wave range and high-field X-ray diffraction experiments have been done successfully.

Structure elucidation and conformational properties of a novel bioactive clerodane diterpene using a combination of high field NMR spectroscopy, computational analysis and X-ray diffraction

The structure of a novel CC clerodane type diterpenoid, namely (+)-19-acetoxy- cis-clerodan-3-ene-15-oic acid 1 was elucidated and its conformational properties were explored using a combination of high field NMR spectroscopy and computational analysis. The structural analysis provided results consistent with those obtained by a single X-ray diffraction study of its dicyclohexylammonium salt. The new clerodane type diterpene isolated in large quantities from Cistus monspeliensis L. leaves was found to exhibit significant antibacterial activity against Staphyloccoci (MIC 50=0.085 mM) and therefore represents a promising lead compound. Interestingly the deacetylated derivative 2 of compound 1 was inactive.

Cryogenfree high field superconducting magnets

A cryogenfree superconducting magnet (CSM) has been realized using Bi-system high temperature superconducting current leads. Although conventional low temperature superconducting magnets wound with NbTi and Nb/sub 3/Sn wires are utilized, liquid helium is no longer required for a magnet operation. Up to now, various kinds of cryogenfree superconducting magnets such as a high field 15 T-CSM, a large bore 5 T-CSM with a 300 mm room temperature bore, and a unique high field X-ray diffraction apparatus combined with a split-pair 5 T-CSM have been successfully developed. Moreover, a split-pair CSM for neutron scattering and a high temperature operation CSM at 20 K employing Ag-sheathed Bi2223 tape have been demonstrated. It is expected that the further rapid progress in a cryogenfree superconducting magnet will be made and high field applications will be enlarged in the near future.