Effect of phosphorus and copper additions on the structure of Pt and Pt–Cu nanoparticles in a radiation-induced reduction method

A facile chemical process has been developed for the preparation of magnetic FeCo nanoparticles. The FeCo nanoparticles were mono-dispersed, obtained by the safe and ecofriendly method, possessed saturation magnetization up to 187 emu/g, and demonstrated excellent chemical stability. In this work, we have studied how to control Fe/Co ratio by variation of precursor ratio, and how to vary particle size from 9.3 to 12.3 nm by surfactant amount used. The cytotoxicity of as-synthesized nanoparticles was investigated after coating with the poly(methyl methacrylate-co-butyl acrylate) by the emulsion process and the results demonstrated high biocompatibility. Similarly, the same synthesis method was used with the single precursor FeO(OH) or Co₃O₄. The results showed that this method can also fabricate 10 nm mono-dispersed spherical Fe₃O₄ particles and self-assembly Co nanoneedles.     

Morphology and chemical state of PVP-protected Pt,Pt–Cu,and Pt–Ag nanoparticles prepared by alkaline polyol method

Well-dispersed, uniform monometallic Pt and bimetallic Pt–Cu, and Pt–Ag nanoparticles protected with PVP have been synthesized by a modified-protocol alkaline polyol method. The nanoparticles were characterized by various methods (TEM, XPS, and XRD) to elucidate the relationship between morphology and preparation variables. The average of monodispersed nanoparticles ranged between 4.1 and 4.9 nm. Core–shell structure was obtained in the case of bimetallic nanoparticles. The core of bimetallic nanoparticles was found to be rich in platinum, whereas the shell contained mostly copper or silver. The final structure of bimetallic nanoparticles was found to be determined by the morphology particles resulted in the first reduction step. Explanations are advanced on the light of experimental results.     

Morphology and structural stability of Pt–Pd bimetallic nanoparticles

The morphologies and structures of Pt–Pd bimetallic nanoparticles determine their chemical and physical properties.Therefore, a fundamental understanding of their morphologies and structural stabilities is of crucial importance to their applications. In this article, we have performed Monte Carlo simulations to systematically explore the structural stability and structural features of Pt–Pd alloy nanoparticles. Different Pt/Pd ratios, and particle sizes and shapes were considered.The simulated results reveal that the truncated octahedron, which has the remarkably lowest energy among all the considered shapes, exhibits the best structural stability while the tetrahedron has the worst invariably. Furthermore, all the structures of Pt–Pd alloy nanoparticles present Pd-rich in the outmost layer but Pt-rich in the sub-outmost layer. Especially, atomic distribution and chemical short-range order parameter were applied to further characterize the structural features of Pt–Pd alloy nanoparticles. This study provides a significant insight not only into the structural stability of Pt–Pd alloy nanoparticles with different compositions, and particle sizes and shapes but also to the design of bimetallic nanoparticles.     

Pt nanoparticles supported over Ce–Ti–O: the solvothermal and photochemical approaches for the preparation of catalytic materials

Ce–Ti–O supports with different Ce/Ti molar ratios were synthesized by the solvothermal method using hexadecyltrimethylammonium bromide. Pt nanoparticles were then supported by photochemical deposition. The shape, size, and structure of these materials were analyzed by high-resolution transmission electron microscopy. The single CeO₂ support was also prepared, consisting of agglomerated cubic particles ranging from ~3 to 8 nm. When titania was combined with ceria, a nanostructured architecture was produced, evidencing the strong influence of Ti in the support structure. Photodeposition of Pt nanoparticles is more efficient on Ce–Ti–O supports than in pristine CeO₂. Crystalline Pt nanoparticles (mainly of ~2 to 4 nm) were detected. The catalytic properties of the materials were tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. It was observed that Pt supported on Ce–Ti–O is more active and selective than Pt on CeO₂ or TiO₂ separately. The catalyst with 40 mol% Ce leads to total conversion of cinnamaldehyde in a few minutes; however, higher selectivity toward the desired product (cinnamyl alcohol) was obtained with higher amounts of Ce (50 mol%).     

Properties of the Ce–Pd–Pt(111) overlayer system

The Pd–Pt(111) and the Ce–Pd–Pt(111) overlayer systems were studied by X-ray photoelectron spectroscopy and low-energy electron diffraction (LEED). Variations in the work function were measured by ultraviolet photoelectron spectroscopy. The Pd overlayer thicknesses were in the range of 1 to 4 monolayers (MLs). The Ce overlayer thicknesses were in the range is of 0.5 to 1.5 MLs. The interfaces were studied for annealing temperatures up to 700°C. Surface alloying or intermixing of Ce, Pd and Pt was observed. Upon deposition at ambient temperatures, Ce forms an overlayer. During annealing, both Pd and Ce were found to dissolve into the Pt substrate. For a Pd coverage of about 1 ML, the Ce–Pd–Pt(111) system was found to be Pt, terminated after annealing to 700°C. For Pd coverage above 1 ML, both Pd and Pt were found to be present at the surface. Cerium was found to be absent from the top surface layer in both cases.     

The influence of the composition of eight-atom Pt–Ir clusters on the magnetic properties

The energetic stability, electronic structure and magnetic properties of Pt_8–nIr_n clusters have been investigated by employing the spin-polarised generalised gradient approximation. The cubic structure is expected to be the effective building block in Ir-rich clusters after optimisation extensively. The average binding energy of all the clusters presents the linear increment trend with iridium atoms, due to the stronger interaction between Ir atoms than Pt atoms. Bader charge analysis shows how tiny charge transfers from iridium to platinum. The atomic moments of Ir are larger than that of Pt, and the Ir-rich clusters show greater moments than the Pt-rich cluster, with the exception of Ir₈ and Ir₇Pt. A unique magnetic property is found in the Pt₄Ir₄ cluster, where two Pt atoms show antiferromagnetic alignment and the other atoms are found to be aligned ferromagnetically.     

Synthesis and characterization of highly textured Pt–Bi thin films

Pt–Bi films were synthesized on glass and thermally oxidized silicon substrates by e-beam evaporation and annealing. The structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) techniques. Single-phase PtBi was obtained at an annealing temperature of 300°C, whereas a higher annealing temperature of 400°C was required to obtain the highly textured γ-PtBi₂ phase. TEM/SAED analysis showed that the films annealed at 400°C contain a dominant γ-PtBi₂ phase with a small amount of β-PtBi₂ and α-PtBi₂ phases. Both the PtBi and γ-PtBi₂ phases are highly textured in these two kinds of film: the c-axis of the hexagonal PtBi phase is mostly in the film plane, whereas the c-axis of the trigonal γ-PtBi₂ phase is perpendicular to the film plane. The electrical resistivity of the film with the γ-PtBi₂ phase was smaller by one order of magnitude than that of the film with the PtBi phase.     

Effect of alloying on the stabilities and catalytic properties of Pt–Au bimetallic subnanoclusters: a theoretical investigation

Density functional theory (DFT) has been applied to study the geometrical and electronic structures and the catalytic properties for NO oxidation of pure Pt and PtAu clusters. The calculated results suggest that Pt₁₀ clusters shows the most stable structure among the pure Pt _n (n = 2–13) clusters with the local maximum Δ₂ E value. The doping of Au atoms reduces the stability of the clusters, and Pt₆Au₄ cluster has the most stable structure among Pt_10?n Au _n (n = 1–7) clusters, due to the closest band centers between Pt and Au atoms (0.83 eV) and the obvious s–p resonance peaks near the Fermi level. Pt₆Au₄ cluster displays the strongest activation of O₂ molecules among Pt_10?n Au _n (n = 0–7) clusters, owing to the clear overlap between O 2p and Pt 6 s and Au 6 s near the Fermi level, and the more positive d band center than the others. The interaction between NO and metals changes slightly in NO/Pt_10-nAu_n (n = 2–7) systems, which is weaker than that in NO/Pt₉Au system, as a result of the decreasing resonance peaks of sp hybridization near the Fermi level. Compared to pure Pt₁₀ cluster, the lower energy barriers and larger reaction energies on Pt₆Au₄ cluster suggest a higher catalytic activity of PtAu cluster for the O₂ dissociation and NO oxidation reactions. Our study provides atomic-scale insights into the nature of the interfacial effect that determines NO oxidation on PtAu cluster catalysts.     

Ab initio study on the ground states,phase stability,and mechanical properties of the Au–Pt system

For the equilibrium immiscible Au–Pt system, ground states are studied based on the results of the cluster expansion method combined with ab initio calculations. The obtained results show that there is no stable phase for the Au–Pt system at 0 K. The further obtained enthalpies of formation for hypothetical crystalline L1₂, D0₁₉, D0₃ structured Au₃Pt and AuPt₃, as well as L1₀ structured AuPt compounds also have positive values. Moreover, elastic constants are predicted from ab initio for the first time for the metastable L1₂ Au₃Pt, AuPt₃ and L1₀ AuPt compound. Finally, there is an imaginary phonon appearing in the obtained phonon spectra, implying an internal instability of the positions of the nuclear coordinates of the L1₂Au₃Pt compound.     

Symmetrizer and Antisymmetrizer of the Birman–Wenzl–Murakami Algebras

Explicit formulas for the symmetrizer and the antisymmetrizer of the Birman–Wenzl–Murakami algebras BWM(r,q) _n are given.     

Tuning of size and shape of Au–Pt nanocatalysts for direct methanol fuel cells

In this article, we report the precise control of the size, shape, and surface morphology of Au–Pt nanocatalysts (cubes, blocks, octahedrons, and dogbones) synthesized via a seed-mediated approach. Gold “seeds” of different aspect ratios (1–4.2), grown by a silver-assisted approach, were used as templates for high-yield production of novel Au–Pt nanocatalysts at a low temperature (40 °C). Characterization by electron microscopy (SEM, TEM, HRTEM), energy dispersive X-ray analysis, UV–Vis spectroscopy, zeta-potential (surface charge), atomic force microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry were used to better understand their physico-chemical properties, preferred reactivities and underlying nanoparticle growth mechanism. A rotating disk electrode was employed to evaluate the Au–Pt nanocatalysts electrochemical performance in the oxygen reduction reaction (ORR) and the methanol oxidation reaction of direct methanol fuel cells. The results indicate the Au–Pt dogbones are partially and in some cases completely unaffected by methanol poisoning during the evaluation of the ORR. The ORR performance of the octahedron particles in the absence of MeOH is superior to that of the Au–Pt dogbones and Pt-black; however, its performance is affected by the presence of MeOH.     

Dynamics of the normal–superconductor phase transition and the puzzle of the Meissner effect

The analysis of Pippard (1950) for the growth of the normal phase into the superconducting phase in the presence of a magnetic field H>H_c$H>H_c$ is applied in reverse to the case H<H_c$H<H_c$ (H_c=$H_c=$ critical magnetic field). We carry out the analysis both for a planar and a cylindrical geometry. As the superconducting phase grows into the normal phase, a supercurrent is generated at the superconductor–normal phase boundary that flows in direction opposite to the Faraday electric field resulting from the moving phase boundary. This supercurrent motion is in direction opposite to what is dictated by the Lorentz force on the current carriers, and in addition requires that mechanical momentum of opposite sign be transferred to the system as a whole to ensure momentum conservation. In the cylindrical geometry case, a macroscopic torque of unknown origin acts on the body as a whole as the magnetic field is expelled. We argue that the conventional BCS-London theory of superconductivity cannot explain these facts, and that as a consequence the Meissner effect remains unexplained within the conventional theory of superconductivity. We propose that the Meissner effect can only be understood by assuming that there is motion of charge in direction perpendicular to the normal–superconductor phase boundary and point out that the unconventional theory of hole superconductivity describes this physics.     

Square Integrability and Uniqueness of the Solutions of the Kadomtsev–Petviashvili-I Equation

We prove that the solution of the Cauchy problem for the Kadomtsev–Petviashvili-I Equation obtained by the inverse spectral method belongs to the Sobolev space H^k(R²) for k 0, under the assumption that the initial datum is a small Schwartz function. This solution is shown to be the unique solution within a class of generalized solutions of the Kadomtsev–Petviashvili-I equation.     

Effect of the Energy of Krypton Ions on the Structure and Hardening of Ti–Cr–N Coatings

Russian Physics Journal -     

Inversion of the Penrose transform and the Cauchy–Fantappie formula

We discuss the construction of an explicit inversion of the Penrose transform with the focus on connections with the Radon transform, multi-dimensional residues and the Cauchy–Fantappie integral formula following to results [1], [2]. The focus is on the new representation (M) of the inverse Penrose transform as a residue. The proof of this formula can be extracted from [1]. This proof includes an explicit computation of this residue (D). In this formula not the exact values of all coefficients but the existence of a differential operator, inverting the Penrose transform (we call this Leibnitz–Newton’s phenomenon) is important. It is similar to local inversion formulas in integral geometry.     

Comparison of Properties of Pt/PZT/Pt and Ru/PZT/Pt Ferroelectric Capacitors

Pb（Zr0.4Ti0.6）O3 film prepared by sol-gel spin coating on a Pt/Ti/SiO2/Si substrate is applied to ferroelectric capacitors with Pt or Ru as the top electrode. For the Pt/PZT/Pt and Ru/PZT/Pt ferroelectric capacitors, although with the same ferroelectric film, different top electrode materials incur different properties of PZT capacitors, such as fatigue, leakage, remanent and saturated polarization, except the similar crystal orientations of the PZT film. After 10^10 switch cycles, the remanent polarizations of the Ru/PZT/Pt and Pt/PZT/Pt capacitors decrease to 70% and 84%, respectively. The leakage current density of the latter increases obviously at positive bias after 108 switch cycles, compared with the former. Different materials for the top electrode bring different conditions at the PZT/top electrode interface. The influence of oxygen-vacancy concentration at the PZT/electrode interface and the influence of oxides of the electrode material at the PZT/electrode interface to charge injection can explain the difference of properties of the PZT capacitors with Pt or Ru as the top electrodes.     

Effect of the donor–acceptor properties of ligands on the spectroscopic and electrochemical properties of mixed-ligand complexes of Pt(II) and Ir(III) with cyclometalated 2-phenylbenzothiazole

The results of the spectroscopic NMR (¹H, ¹³C, and ¹⁹⁵Pt), infrared, optical, and voltammetric characteristics of the mixed-ligand complexes of Pt(II) and Ir(III) with metalated 2-phenylbenzothiazole and tert-butylisocyanide (tBuNC), acetonitrile (AN), ethylenediamine (En), O-ethyldithiocarbamate (Exn^–), and diethyldithiocarbamate (Dtc–) ions are presented. It is demonstrated that the change in donor–acceptor interaction of ligands tBuNC, AN, En, Exn^–, and Dtc^– with metal leads to an increase in the energy of the highest occupied molecular orbital of the complexes and is accompanied by a shift of the cathode potential of the metal-centered oxidation, a bathochromic shift of the spin-allowed and spin-forbidden metal-tocyclometalated ligand optical charge transfer transitions, and an increase the degree of mixing of the ¹MLCT and triplet intraligand states, responsible for the phosphorescence of the complexes.     

Effect of copper on the structure–phase transformations and the properties of quasi-binary TiNi–TiCu alloys

The effect of copper alloying up to 25 at % on the structure–phase transformations and the physicomechanical properties of ternary alloys from the quasi-binary TiNi–TiCu section is studied by measuring the physicomechanical properties, transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction (XRD). The data of temperature measurements of the electrical resistivity and the magnetic susceptibility and XRD data are used to plot a general diagram for the thermoelastic B2 ? B19', B2 ? B19 ? B19', and B2 ? B19 martensitic transformations, which occur in the alloys upon cooling as the copper content increases in the ranges 0–8, 8–15, and 15–25 at % Cu, respectively. The experimental results are compared to the well-known data, including differential scanning calorimetry data, obtained for these alloys. The changes in the mechanical properties and the microstructure of the alloys in the state of B19 or B19' martensite are discussed.