Yoshihisa Muranushi

Optical characterisation of single crystal 2H-SnS2 synthesised by the chemical vapour transport method at low temperatures

Optical characterisation has been performed for single crystal 2H-SnS2 synthesised by the chemical vapour transport method at low temperatures. The optical absorption spectra measured in the normal-incidence geometry at room temperature show an indirect transition with an energy gap Eg=2.17+or-0.01 eV. Photoluminescence spectra at liquid helium temperature indicate two series of phonon replica of excitons with phonon energies LO1=62 meV and LO2=70 meV, where the zero phonon lines are 2.310 eV and 2.224 eV respectively.

Photoconductive properties of single-crystal 2H-SnS2

Abstract Photoconductive properties of single-crystal 2H-SnS2, grown by a new chemical vapor transport method at low temperature, were investigated at room temperature with the direction of current flow normal to the c-axis. The photocurrent response can be observed for exciting photon energies lower as well as higher than the band gap, and is found to increase linearly with the light intensity and the applied bias voltage. Photoresponse times of faster than 5 ms, of several tens of seconds and 10 h are recognized besides the relaxation time previously reported as 1–10 s. Discussions are presented with emphasis on the slow photoresponse processes which are not caused by surface states.

Electrical characterization of 2H-SnS2 single crystals synthesized by the low temperature chemical vapor transport method

Abstract Single crystals of 2H-SnS 2 synthesized by the chemical vapor transport method at 450°C were found to be n -type semiconductors with room temperature properties such as specific resistance ρ = 7.30 ohm cm, Hall mobility μ H = 18.3cm 2 V −1 s −1 , and carrier density n = 5.21 × 10 16 cm −3 in the c -plane according to the van der Pauw conduction measurement. The mobility μ H decreases below 200 K and shows a peak around 65 K. μ H shows a non-linear variation with the injection current and shows a peak at 1 mA.

Insertion of lithium into vanadium molybdenum oxides

Abstract Chemical insertion of lithium into V 2 O 5 , Mo 0.1 V 1.8 O 4.8 and MoV 2 O 8 by LiI has been investigated. The limiting lithium content in all oxides is Li/V = 0.5, suggesting that only the V component is responsible for the lithium insertion. For V 2 O 5 , two potential plateaux correspond exactly to two-phase coexistent crystal structures with different van der Waals gap distances; the interaction energy between inserted lithium is attractive. By contrast, as the ratio of V substitution in Mo increases, the two-phase behaviour decreases, and the interaction between Li + cations becomes repulsive. These insertion characteristics have been analyzed in relation to structural changes in VO 5 polyhedra.

Chemical and structural characterization of SnS2 single crystals grown by low-temperature chemical vapour transport

Chemical and structural characterization has been performed for thick (100–600 μm) and thin (10–100 μm) 2H/4H inter-polytype SnS2 crystals grown by low-temperature chemical vapour transport in the reverse temperature gradient geometry. X-ray diffraction shows that the 2H/4H-SnS2 phase transforms to single-crystal 2H-SnS2 in 6–12 months. The S/Sn ratio is 2.02±0.01 in thick crystals and 2.01±0.01 in thin crystals. Thermogravimetric/differential thermal analysis and the other characterization techniques show no difference between the two types of crystal. Extremely small quantities of carbon and oxygen and some chlorine were detected by secondary ion mass spectroscopy and/or X-ray photoelectron spectroscopy (XPS). These elements are concentrated at the surface. The XPS data show a chemical shift of tin and sulphur in the surface layer, which is probably caused by the adsorbed carbon and oxygen; however, it cannot be explained by the formation of the usual oxides of tin and sulphur.

Chemical analysis of photoassisted intercalation reaction of SnS2 single crystal under cathodic polarization

Abstract Cathodic reactions at (001) SnS2 single crystal—KCl aqueous solution were investigated analytically both in the dark and under illumination. Reductive decomposition of the SnS2 host occurred in the dark besides intercalation of the hydrated K+ ion. However, the former was inhibited by illumination.

Sulfur diffusion of single crystal 2H-SnS2 on Ag paste

Abstract Investigation with XPS showed that surface diffusion of sulfur occurs on Ag paste to form Ag 2 S at room temperature from a single crystal 2H-SnS 2 synthesized by the chemical vapor transport method at low temperature.

Lithium insertion characteristics of α-phase NayV2O5

Abstract To understand the characteristics of V 2 O 5 as a host material for lithium insertion, Na y V 2 O 5 and its lithiated compounds were prepared. It was revealed from their structural and electrochemical behaviours that (1) Na y V 2 O 5 with y x Na y V 2 O 5 lithium ions also behave ideally and randomly distributed unoccupied sites offered by previously inserted sodium ions will help to weaken the host mediated interguest interaction.

Characteristics of a rechargeable cell constructed by coupling Nax−yWO3 and Nax−yPd3O4

Abstract Electrochemical behaviour of NaPd 3 O 4 and of Na x WO 3 has been investigated in 0.5 M H 2 SO 4 solution at 25 °C. Sodium depleted surface layer can be formed on the electrode surface of NaPd 3 O 4 by anodic pre-polarization and this surface layer absorbs or desorbs H + reversibly at around 1.0 V versus SHE. Furthermore, a rechargeable cell with a long cyclability can be constructed by coupling Na x − y WO 3 and Na 1− y Pd 3 O 4 in an acidic solution.

Anodic behaviour of sodium tungsten bronze in neutral solutions

Abstract The anodic behaviour of sodium tungsten bronze in neutral solutions was investigated. Preferential dissolution of the sodium component occurs from the rest potential, and at about 0.7 V (measured with reference to a standard hydrogen electrode) dissolution of the tungsten oxide component begins to occur. The dissolution of the tungsten oxide component gives a marked increase in the current density. At more noble potentials tungsten bronze is passivated, and the same surface film as that for passivation of metallic tungsten seems to be responsible for the passivation of sodium tungsten bronze.