Hiroyuki Yamada

Magnetic, Electric and Structural Properties of β-AxV 2O 5 (A= Na, Ag)

Physical properties of β- A x V 2 O 5 ( A = Na, Ag) have been systematically reconsidered from structural, electric, and magnetic points of view. We prepared samples, both powder and single crystal, with precise composition for this purpose. The single crystals have been successfully grown by a self flux method using NaV 3 O 8 as a flux. The precise adjustment of x was performed by embedding the as-grown crystals in a large amount of powder and heating them. β-Na 0.33 V 2 O 5 was not a conventional semiconductor but a possible anisotropic metal at higher temperatures. It exhibited a metal-insulator transition at 136 K, suggesting a charge ordering. The ordered structure underwent a magnetic ordering with T c = 24 K. We also observed a development of 1×2×1 superstructure below 230 K, suggesting an ordering of the intercalated ion. Those transitions similarly occurred in β-Ag 0.33 V 2 O 5 . The deviation from x = 0.33 drastically decreased the transition temperatures or magnitudes of anomalies at the transi...

Low temperature X-ray study of β-AxV2O5

Abstract The vanadium oxide bronzes β(β′)-A x V 2 O 5 of A=Na ( x =0.33), A=Sr ( x =0.33) and A=Cu ( x =0.65) having one-dimensional chain and ladder along the b -axis were studied by X-ray diffraction measurements. We observed the satellite reflections of q =1/2 b ∗ due to A-site cation ordering below 260xa0K for A=Na and room temperature for A=Sr. And then, we observed the satellite reflections of q =1/6 b ∗ below the metal–insulator transitions of 135xa0K for A=Na and 165xa0K for A=Sr. Moreover, we found the reflection accompanying the symmetry breaking below 255xa0K for A=Cu, corresponding to the slight anomaly in the resistivity of the metallic behavior. The superstructure analyses indicate the characteristic movement of vanadium atoms in the ladder, suggesting the charge disproportionation below 135xa0K for A=Na and 255xa0K for A=Cu.

Simplified oxidation mechanism of DME applicable for compression ignition

A simplified reaction model of dymethyl ether (DME) oxidation has been developed by extracting essential elementary reactions from a previous detailed mechanism. It consists of 23 reactions for 23 species without modification of rate coefficients in low temperature oxidation of the original model. Spatially non-dimensional calculations were conducted along with HCCI compression profiles using SENKIN code in CHEMKIN package. Good agreement with the detailed model was obtained in terms of ignition timing and profiles of species such as DME, HCHO, O 2 , H 2 O 2 , and CO as functions of intake gas temperature, equivalence ratio, and intake pressure. Adding a few reactions to the mechanism, the effective range of the model was extended to rich side, where CO emission is significant. Effect of methanol addition as an ignition suppressor was also properly described.

Charge order and quasi-one-dimensional behavior in β(β′)-AxV2O5

Abstract Quasi-one-dimensional conductor β(β′)-A x V 2 O 5 (A=Li, Na, Ag, Ca, Sr, Cu) was investigated for its electric and magnetic properties. The β-A 0.33 V 2 O 5 (A=Li, Na, Ag, Ca, Sr) phases show a phase transition accompanied by a charge separation and a charge order. The low temperature phase of β-A + 0.33 V 2 O 5 shows a long-range magnetic order at lower temperature whereas β-A 2+ 0.33 V 2 O 5 shows a formation of spin gap without any magnetic order. The magnetic properties of the low temperature phases strongly suggest a linear chain for β-A + 0.33 V 2 O 5 and a two-leg ladder chain for β-A 2+ 0.33 V 2 O 5 as a charge ordered pattern of magnetic V 4+ ions. A quasi-one-dimensional conductor β′-Cu 0.65 V 2 O 5 shows a superconducting transition under high pressure around 4 GPa at 5 K.

Preparation and magnetic properties of manganese(II) phthalocyanine thin films

We report the molecular beam epitaxy (MBE) growth of the manganese(II) phthalocyanine thin films with unique crystal structure and the measurement of their magnetic properties. The epitaxial films were grown on hydrogen-terminated Si(111) substrates. Reflection high energy electron diffraction observations showed that the crystal structure of the films is different from that of the bulk crystal. A large magnetic anisotropy was observed in the measurements with the SQUID magnetometer. The films did not show canted ferromagnetism which is usually observed in the β-type crystal of manganese phthalocyanine. The magnetic susceptibility measured with magnetic field normal to the substrate obeyed the Curie–Weiss law with a negative Curie–Weiss constant, indicating the existence of the antiferromagnetic interaction. The negative Curie–Weiss constant was also observed in disordered films of manganese phthalocyanine. The variation of magnetic properties between the bulk crystal and the films is explained in terms o...

Buffer-gas cooling of antiprotonic helium to 1.5 to 1.7 K, and antiproton-to–electron mass ratio

Exotic molecule tests fundamental symmetry Spectroscopy of exotic molecules can offer insight into fundamental physics. Hori et al. studied the transition frequencies of an unusual helium atom in which one of the two electrons was substituted by an antiproton, the negatively charged antiparticle partner of the proton (see the Perspective by Ubachs). The antiprotonic helium was cooled down to low temperatures to allow the frequencies to be measured with high precision. The extracted mass of the antiproton (relative to the electron mass) was in good agreement with previous measurements of the proton mass. This finding is in keeping with the implications of the combined charge, parity, and time-reversal symmetry of physical laws. Science, this issue p. 610; see also p. 546 Spectroscopy of a cold exotic molecule yields a precise value of the antiproton mass relative to the mass of the electron. Charge, parity, and time reversal (CPT) symmetry implies that a particle and its antiparticle have the same mass. The antiproton-to-electron mass ratio Mp¯/me can be precisely determined from the single-photon transition frequencies of antiprotonic helium. We measured 13 such frequencies with laser spectroscopy to a fractional precision of 2.5 × 10−9 to 16 × 10−9. About 2 × 109 antiprotonic helium atoms were cooled to temperatures between 1.5 and 1.7 kelvin by using buffer-gas cooling in cryogenic low-pressure helium gas; the narrow thermal distribution led to the observation of sharp spectral lines of small thermal Doppler width. The deviation between the experimental frequencies and the results of three-body quantum electrodynamics calculations was reduced by a factor of 1.4 to 10 compared with previous single-photon experiments. From this, Mp¯/me was determined as 1836.1526734(15), which agrees with a recent proton-to-electron experimental value within 8 × 10−10.

Controlling mechanism of ignition enhancing and suppressing additives in premixed compression ignition

Abstract Controlling ignition timing in the homogeneous charge compression ignition (HCCI) of dimethyl ether (DME) by adding methanol and ozone has been studied in a motored engine. In the standard pressure profile analysis, reduction of the first stage (cool ignition) heat release with methanol addition and consequent retardation of the second stage (hot ignition) was confirmed. Composition analysis, conducted under moderate, single cool ignition conditions, exhibited liner reductions of fuel consumption and formaldehyde formation. These observations were well reproduced by the detailed chemical kinetic model of Curran et al. for DME. A simple formulation accounting for the retarding effect was established. In contrast, acceleration with ozone addition is caused by the increase of heat release in the cool ignition taking place at a lower temperature. The cool ignition composition analysis showed increases of fuel consumption that are remarkable in lower equivalence ratio. Inclusions of ozone decomposition forming O + O2 into the model enabled good reproduction of these features. It was inferred that the early radical supply from ozone reduced the cool ignition onset temperature significantly, where a stable intermediate accumulates owing to slow decomposition, and that the resultant reduction of formaldehyde formation induced the longer chain duration.

NMR study of local magnetic and electronic properties of vanadium bronzes

Abstract 51 V NMR experiments have been performed to study the local magnetic and electronic properties of the vanadium oxide bronzes β-AV 6 O 15 (A=Na and Ca). We observed a drastic change in the 51 V NMR spectrum due to a charge-ordering transition in both oxides. The ground state of NaV 6 O 15 is found to be an antiferromagnetically ordered state, whereas that of CaV 6 O 15 is nonmagnetic. This is closely related with the number density of V 4+ ions and the structure of the charge ordering.

Time-resolved measurements of low concentration aromatic hydrocarbons in diesel exhaust using a resonance enhanced multi-photon ionization method

Abstract Time-resolved measurements of the concentration of volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) in exhaust from a diesel vehicle fitted with an oxidation catalyst and operated in JE05 mode are performed at a sensitivity of 10 ppb using a supersonic jet/resonance enhanced multi-photon ionization (Jet-REMPI) method. The concentrations of benzene, naphthalene, and phenol in exhaust from the test vehicle are measured before entering and after exiting from the oxidation catalyst. The total hydrocarbon (THC) is measured simultaneously using a constant volume sample (CVS) instrument fitted with a flame ionization detector (FID). Concentration changes of benzene, naphthalene and phenol are recorded at 1 s intervals and quantified using standard samples. Comparison of these signals with the real-time THC data shows that the time dependence of the individual species is almost the same as that of the THC before the oxidation catalyst but substantially different after.

Structural and Electric Properties of β′-CuxV 2O 5

Single crystals of β ′ -Cu x V 2 O 5 have been successfully grown by a self flux method, and their structural, magnetic, and electric properties have been systematically investigated as a function ...