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The structural changes and superconductivity in the layered non-stoichiometric niobium diboride compound were systematically studied for both of niobium-deficient and boron-deficient phases by X-ray diffraction analysis and magnetic susceptibility measurements. The niobium and boron vacancies were found to have different effects on the crystal lattice parameters and superconducting properties; superconductivity only exists in niobium-deficient phases with a clear enhancement of inner-plane B–B bonding and the increase of inter-plane distance, while boron vacancies have the opposite effect of enhancing the Nb–B bonding and breaking the superconductivity. A main superconducting phase with Nb0.83B2 composition was obtained with Tc ∼ 9.3–9.9 K, and a = 3.102(1) A and c = 3.322(2) A under the optimum sintering conditions. The low temperature specific heat was measured for three high-pressure synthesized superconducting samples to reveal the origin the increase of Tc with the niobium deficiencies.

We have succeeded in synthesizing a new member of ternary silicide NaAlSi with a superconducting transition temperature T c−onset = 7 K by high pressure technique. The crystal structure of NaAlSi is the layered diamond-like structure with a space group of P 4/ nmm (no. 129, Z = 3) and without inversion symmetry. The superconducting properties in NaAlSi have been investigated by means of DC and AC magnetic susceptibility measurements. These magnetic responses indicate that NaAlSi belongs to a conventional type-II superconductor with a Ginzbrug–Landau parameter κ = 13.8. From the band structure calculations, we found that the hole band of Si p- and electron Al s-orbitals play an important role for the superconductivity in this system.

We have performed high-resolution angle-resolved photoemission spectroscopy on layered polymorph series of $1H\ensuremath{-}, 5H\ensuremath{-}$, and $6H\ensuremath{-}\mathrm{CaAlSi}$, which exhibit superconductivity below 6.5, 5.7, and 7.7 K, respectively. While the overall band structure in the valence-band region is similar among these compounds, the volume of the Fermi surface at the $M$ point and the magnitude of the superconducting gap are markedly different from each other. Implications of such variation in the electronic structure due to the superstructure along the $c$ axis are discussed in relation to the physical properties of CaAlSi.

A comprehensive magnetic and superconducting phase diagram determined by muon spin rotation/relaxation ( μ SR ) is presented for Ca 2 - x Na x CuO 2 Br 2 which has apical bromine atoms. Evidence for antiferromagnetic (AF) order in lightly doped samples and that for quasi-static spin glass (SG)-like state in moderately doped ones are obtained by ZF- μ SR at low temperatures. While the phase diagram is qualitatively similar to that in typical 2-1-4 cuprates including Ca 2 - x Na x CuO 2 Cl 2 and La 2 - x Sr x CuO 4 , it exhibits a slight shift (expansion) over the x axis.

We present a combined experimental and theoretical study of the effects of pressure on T_c of the hexagonal layered superconductors nH-CaAlSi (n = 1, 5, 6), where nH labels the different stacking variants that were recently discovered. Experimentally, the pressure dependence of T_c has been investigated by measuring the magnetic susceptibility of single crystals up to 10 kbar. In contrast to previous results on polycrystalline samples, single crystals with different stacking sequences display different pressure dependences of T_c. 1H-CaAlSi shows a decrease of T_c with pressure, whereas 5H and 6H-CaAlSi exhibit an increase of T_c with pressure. Ab-initio calculations for 1H, 5H and 6H -CaAlSi reveal that an ultrasoft phonon branch associated to out-of-plane vibrations of the Al-Si layers softens with pressure, leading to a structural instability at high pressures. For 1H-CaAlSi the softening is not sufficient to cause an increase of T_c, which is consistent with the present experiments, but adverse to previous reports. For 5H and 6H the softening provides the mechanism to understand the observed increase of T_c with pressure. Calculations for hypothetical 2H and 3H stacking variants reveal qualitative and quantitative differences., Comment: 6 pages, 5 figures

We report muon spin relaxation measurements on two Ti3+ containing perovskites, LaTiO3 and YTiO3, which display long range magnetic order at low temperature. For both materials, oscillations in the time-dependence of the muon polarization are observed which are consistent with three-dimensional magnetic order. From our data we identify two magnetically inequivalent muon stopping sites. The muon spin relaxation results are compared with the magnetic structures of these compounds previously derived from neutron diffraction and muon spin relaxation studies on structurally similar compounds., Comment: 11 pages, 4 figures

Tunneling spectroscopy using a break-junction technique has been conducted to determine the superconducting gap structure of the ternary silicide-layered superconductor CaAlSi with and without superstructure. We find that the tunneling conductance in CaAlSi shows a single gap feature, which can be described by the BCS density of states. The gap size $\ensuremath{\Delta}$ obtained from the tunneling conductance in CaAlSi without superstructure is estimated to be approximately $1.0\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, corresponding to a weak-coupling gap ratio. On the other hand, for a specimen with superstructure, the largest gap, $\ensuremath{\Delta}=1.5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, significantly deviates from the BCS value, indicating strong-coupling superconductivity. These results demonstrate systematic variations in the pairing interaction with superstructure formations, which are consistent with heat capacity measurements.

We report on the detailed crystal structure and superconducting properties in the single-crystalline SrAlSi by means of synchrotron X-ray diffraction technique and systematic magnetization measurements. Although SrAlSi exhibits a clear no sign of superlattice reflection, the anisotropic parameter for magnetic response in SrAlSi is almost equivalent to that of superstructured CaAlSi. It is inferred from these results that the electronic ground state in SrAlSi shows quasi-two-dimensional characteristics, and its dimensionality is irrelevant to the superstructured system.

When high-strength concretes are conveyed by pumping, the pumping pressure may increase and the flowability of high-fluidity concrete may be greatly decreased. This is a problem for construction of concrete-filled tubular steel columns. In this study, pumping tests and filling tests of steel tubular model columns with several kinds of high-fluidity concrete having a water/cement ratio of 30% were conducted. Silica fume results in better pumpability. The pressure loss reflects good correlation to the plastic viscosity of the concrete calculated from the time taken for it to discharge from an inverted slump cone. When the concretes used in the tests were pumped into tubular columns, the cavity area under the diaphragm plates was less than 10% and the core strength obtained at 91 days was over 80 N/sq mm. If the slump flow of concrete at the top of the column is more than 45 cm, it can be expected that the column will be filled well. The pressure of concrete at the bottom of the column is approximately 1.2 times the head pressure.

The full-potential linear augmented plane-wave calculations have been applied to investigate the systematic change of electronic structures in CaAlSi due to different stacking sequences of AlSi layers. The present ab-initio calculations have revealed that the multistacking, buckling and 60 degrees rotation of AlSi layer affect the electronic band structure in this system. In particular, such a structural perturbation gives rise to the disconnected and cylindrical Fermi surface along the M-L lines of the hexagonal Brillouin zone. This means that multistacked CaAlSi with the buckling AlSi layers increases degree of two-dimensional electronic characters, and it gives us qualitative understanding for the quite different upper critical field anisotropy between specimens with and without superstructure as reported previously., Comment: 4 pages, 4 figures, to be published in J. Phys. Soc. Jpn

We report on magnetic, transport, specific heat and tunneling measurements of NbB 2 with the maximum superconducting critical temperature T c ∼10 K. The essential superconducting properties have been investigated through mapping out the critical field phase diagram, from which it is turned out to be type II superconductor with a small Ginzbrug–Landau parameter κ∼2.2. Both the tunneling and specific heat measurements indicate that our NbB 2 specimen has a single gap and s -wave pairing symmetry with a weak-coupling limit. The electron–phonon coupling constant is estimated to be λ ep =0.71±0.02, suggesting that the maximum T c of NbB 2 can be explained by the McMillan formula.

Since, according to the previous works, though it depends on the nature of aluminium alloys, the effect of alcohol-phosphate treatment prior to enameling is generally recognized, this time the special primer containing phosphoric acid which is etch type is investigated successively. The surface proparations by chemical treatments of aluminium alloys are not needed at all in the case of “Etch-priming”, hence the specimens are primed first and then coated with zinc chromate phthalic resin enamel. And bending-test, drawing-test, erichsen-test and corrosion-tsst are performed. The one of the vehicles used to “Etch-primer” is based on poly-vinylacetate and the other one on copolymers of vinyl acetate and methyl metacrylate in the works. The results of these tests are useful for comparative evalution. In short, in the vehicle based on poly-vinylacetate etch-priming coats are effec tive even in phospholic acid addition of only 0.8%, but in that based on co-polymers of vinyl acetate and methyl metacrylate not yet effective.