High‐Quality Three‐Dimensional Nanoporous Graphene

We report three‐dimensional (3D) nanoporous graphene with preserved 2D electronic properties, tunable pore sizes, and high electron mobility for electronic applications. The complex 3D network comprised of interconnected graphene retains a 2D coherent electron system of massless Dirac fermions. The transport properties of the nanoporous graphene show a semiconducting behavior and strong pore‐size dependence, together with unique angular independence. The free‐standing, large‐scale nanoporous graphene with 2D electronic properties and high electron mobility holds great promise for practical applications in 3D electronic devices.     

Antiferromagnetic ordering and metamagnetism in PrCuSi

A variety of physical properties measured on the hexagonal rare-earth intermetallic compound PrCuSi are presented. We provide compelling evidence for antiferromagnetic ordering at T_N = 5.1 K in this compound, in contrast to the former claim of ferromagnetic ordering at 14 K. The antiferromagnetic order is, however, found to be unstable in applied magnetic fields, becoming ferromagnetic beyond a metamagnetic transition at a field of 0.7 T at 2 K. It is argued that the magnetism in PrCuSi has the ingredients of a tricritical phase transition at the intersection of paramagnetism, ferromagnetism, and antiferromagnetism.     

Influence of temperature and time of isothermal holding on the viscosity and crystallization processes of Al-Y melts close to a eutectic structure

We investigate the temperature and time dependences of viscosity of Al₉₉Y₁, Al₉₇Y₃, Al₉₅Y₅ melts in the range from liquidus to 1200°C. By metallographic, XRD, and differential thermal analyses, we study how the time of isothermal holding of melts influences the structure of ingots during hardening.     

Scanning tunneling microscope light emission spectra of polycrystalline Ge2Sb2Te5 and Sb2Te3

We have observed scanning tunneling microscope light emission (STM-LE) spectra of Ge₂Sb₂Te₅ and Sb₂Te₃. Although these chalcogenide alloys exhibit band gaps less than 0.5 eV, the STM-LE was observed with a narrow spectral width at a photon energy of 1.5 eV for both materials. By analyzing its bias voltage, polarity, and temperature dependencies combined with recently reported theoretical electronic structures, we concluded that the STM-LE is excited by electronic transitions taking place in the local electronic structure having a direct gap-like shape with a band gap of 1.5 eV, commonly found in the electronic structures of both materials.     

Chemically shortened multi-walled carbon nanotubes used as anode materials for lithium-ion batteries

An easy chemically cutting process, modified Hummers' method, was proposed to treat multi-walled carbon nanotubes, successfully cutting pristine long, entangled carbon nanotubes into hydrosoluble pieces, mostly less than 200 nm. This short, chemically oxidized carbon nanotube was then applied as an anode material for lithium-ion batteries. The as-prepared material possessed higher reversible capacity and coulombic efficiency. The intrinsic factors were explored by X-ray photoelectron spectroscopy and cyclic voltammetry.     

A study of the effects of mass transfer under quasi-spherical loading of a composite spherical sample

Metallography and electron probe microanalysis were used to study the structure of a composite ball, 60 mm in diameter, subjected to quasi-spherical shock-wave loading. The sample consisted of spherical steel and brass shells and a brass cylinder at the center. Converging shock waves were generated by a spherical HE charge, which was initiated at several points uniformly distributed over its external surface. The pressures at the surface and center of the sample were ～40 and ～100 GPa, respectively. Brass and steel were observed to penetrate into the narrow channels of the joints between the halves of the shells and into the compact material. The depths of penetration into the joints and compact material were 3.2 and 0.3 mm, respectively. Mass transfer occurred along the radius from the surface to the center of the sample and in the opposite direction. The mass transfer effects revealed are of hydrodynamic nature.     

Ferro-and antiferromagnetic ordering in LaMnO3+δ

A neutron diffraction study of the crystalline structure and magnetic state of LaMnO_3+δ samples with different deviations from oxygen stoichiometry has been made at 4.2 K. It is shown that annealing at reduced oxygen pressure is accompanied by transformation of the magnetic structure from ferromagnetic, with magnetic moments parallel to the b axis, to antiferromagnetic, with the wave vector k=0 and the moments along the a axis (space group Pnma). A comparison of experimental with expected Mn ion moments suggests that magnetic order does not extend throughout the sample volume. Part of the Mn ions form magnetic clusters ～20 Å in size.     

Electron phase transition in TiNi?

The optical and X-ray photoelectronic spectra and temperature dependence of magnetic susceptibility are investigated. It is found that at martensitic transformation in TiNi electron redistribution occurs which is accompanied by cardinal change of Fermi surface. Based on the data obtained in B2-structure (CsCl) E_F is assumed to lie in the kT-vicinity of the N(E) peak that determines the tendency to the structural instability of B2.     

Symmetry analysis in neutron diffraction studies of magnetic structures: 2. Changes in periodicity at magnetic phase transitions

A study is made of the translational properties of magnetic structures. The first stage of magnetic structure decoding, which is aimed at determining the magnetic lattice of the crystal, is described in detail using the information obtained from neutron diffraction patterns. Attention is given to the necessity of introducing the notion of transition channel which consists in specifying the wave vector star and the set of its arms describing a given transition. For each of the 14 Bravais lattices of the initial crystal we consider all the possible transition channels with symmetric stars and determine the corresponding magnetic lattices. The results are presented as a table which contains magnetic reflections corresponding to each channel. The notion of wave vectors of a magnetic structure is made more precise and the rule of their translation from the diffraction language into that of group theory is given.     

Power absorbed by a subsystem in the response theory

A macroscopic system which consists of a set of interacting subsystems in an external field is considered. A convenient formula is derived for the mean energy Q_j absorbed per unit time by a subsystem. The expression obtained for Q_j takes into account that in general the Hamiltonian H of such a system does not coincide with the sum of the Hamiltonians of the subsystems H_j; Q_j appears to be the same for various possible definitions of H_j's.