Saiko Negishi

Electron Charge Density Study on the Bonding Nature in MoO3

The accurate electron charge density distributions of MoO 3 have been investigated by analyzing the synchrotron radiation X-ray powder diffraction data using the MEM (Maximum Entropy Method)/Rietve...

Simulation of Atomic Distribution of Guest Atoms in Layered 1T-TiS 2 Crystal using Monte Calro Method and Its Effect on the Magnetic Properties and Local Structures

Monte Carlo simulations of atomic distribution of intercalated guest atoms in the layered 1T-TiS 2 have been performed by taking into account attractive or repulsive pair-interactions between the neighboring guest atoms in the a -axis plane and along the c -axis of the crystal lattice (lattice size for computation: 18×18×6). X-ray diffraction patterns are calculated from the atomic distributions obtained using four kinds of pair-interactions, in qualitative agreement with the experimental data of the 2 a ×2 a ×2 c short-range ordered structure for x =0.15, and superlattices of \(2\sqrt{3}a\times 2a\times 2c\) for x =0.25 and \(\sqrt{3}a\times\sqrt{3}a\times 2c\) for x =0.333 with fractional site occupancy in Fe x TiS 2 . From the calculated atomic distributions, we have evaluated the number of neighboring guest atoms, the formation of clusters, and percolation cluster, as well as its dimension, all of which are responsible for the dynamical relaxation behaviors of the thermoremanent magnetization observed...

EXAFS and XANES studies on 3d transition metal intercalation compounds MxTiS2

Abstract EXAFS and XANES spectra of Ti K-edge have been measured for 3d transition metal intercalation compounds M x TiS2 (M = Mn, Fe, Co and Ni; x ≤ 0.33). We have found that the interatomic distance between Ti and the first nearest neighbor S atoms, R(Ti-S), increases with the guest concentration x. The variation in XANES spectra with x reveals the reduction of the valence state of Ti atoms upon intercalation of M. From these results as well as the M K-edge EXAFS data studied previously, we have proposed a simple model on the local structure of M x TiS2 to reproduce the observed values of R(Ti-S) by averaging local shift of S atoms caused by intercalation.

Observation of the fracture plane of potassium iodide formed at the pressure-induced phase transition

The fracture plane of potassium iodide which experienced the phase transition at high pressure was observed with the stereoscopic microscope at zero pressure, where the pressure was applied in the controlled rate and removed rapidly in various time intervals, Δ t s, after the initiation of the phase transition was detected. The outer region of the fracture plane observed, domain B, was bumpy and random, suggesting that this region experienced the phase transition. However, the inner region of the fracture plane, domain F, was smooth, flat and considerably cleavable, indicating that this domain remained almostly at B1 in the case of very small Δ t . Although increasing Δ t did not alter the geometrical appearance of the fracture plane, the cleavability in phase F was rather lost, which leads us to the conclusion that the transition following the formation of domain B proceeded over the entire volume of domain F.

A new type of bulk quantum Hall effect in Bi2−xSnxTe3 crystals

Abstract We have found a new type of bulk quantum Hall effect (b-QHE) in layered crystals of Bi 2 Te 3 and Bi 2− x Sn x Te 3 ( x =0.005, and 0.0075), whose Hall resistivities exhibit clear Hall plateaus at odd- and even-filling factors, respectively, and the corresponding resistivity minima appear not at the center but at the onset of the Hall plateaus. The charge transfer from the lower valence band in the former or Sn-induced impurity band (IB) in the latter to the upper valence band is found to be the key point for b-QHE.

Montecarlo Simulation of Intercalated Atomic Distributions in Layered Dichalcogenide

Abstract Atomic distributions of intercalated guest atoms into layered dichalcogenide have been simulated taking into account the interactions between the first and second nearest neighboring guest atoms in the triangular lattices stacked with 6 layers (lattice size 18 × 18 × 6) using a MonteCarlo method. With these distributions, the X-ray patterns of Fe x TiS2 with x = 0.25 having the 2√a × 2a × 2c superlattice with the fractional site occupancy have been reproduced qualitatively by averaging the intensities for different patterns obtained by different random seeds.

Possibility of Charge Density Wave Transition in Tellurium Molybdenum Oxide TeMo5O16

Electrical resistivity ρ, specific heat C, and magnetic susceptibility χ have been measured over 4.5 K - 300 K for the ternary molybdenum oxide TeMo5O16 grown by a chemical vapor transport method. The temperature dependence of ρ and C shows an anomalous behavior around 170 K and a remarkable peak at 179 K, respectively. Furthermore, the magnetic susceptibility, subtracted by a Curie-Weiss component from the observed values, shows a decrease below 180 K. These results suggest that in TeMo5O16 the charge density wave transition occurs at Tc=179 K due to a reduction of the Fermi surface.

Large negative magnetoresistance of intercalation compound MnxTiS2

Abstract A relatively large negative magnetoresistance has been evidenced in intercalation compounds Mn x TiS2 (0 0.03, a ‘Mn-derived band’ is formed near the Fermi energy. In the layered structure of Mn x TiS2, the carrier transport takes place along the host TiS2 layers and through the interlayer spaces via intercalated Mn atoms. The observed negative magnetoresistance can be reasonably explained by existing spin fluctuation theories.