The a- and b-axis resistivities and the a-axis magnetoresistivities applying magnetic field (B) along all three crystallographic axes in non-superconductive PrBa2Cu4O8 single crystals have been measured using four-probe method. Resistivitiy along the b-axis (parallel to double-chains) showed a highly conductive behavior, of which the origin is attributed to the double-chains because of a large anisotropic conduction between a- and b-axis directions. However, a metallic behavior along the a-axis was also observed in temperature region below 130 K, which could be understood in terms of presence of finite and coherent inter-chain interaction along the a-axis direction. This conclusion is derived from good agreement with values of mean-free path length in the double chain, lchain estimated from both the ρb-T curve and the a-axis MR applying B//c using quasi-one-dimensional (quasi-1D) band model.

Ion implantation experiments were carried out on a single grain Al-Pd-Mn icosahedral quasicrystal. The influence of Re or Au dopant on the thermopower and the electrical resistivity has been measured. Comparison with ternary and quaternary alloys produced by usual metallurgical techniques is made. The results indicate that the efficiency of this quasicrystalline alloy as a thermoelectric material can be improved by adjusting composition and structural quality, as well as by the addition of a small amount of Re, whereas Au implantation is inefficient in that respect.

The origin of the pseudogap across the Fermi level was investigated by analyzing the electronic structure calculated in the framework of the LMTO-ASA method for the RT-type Al-Mg-Zn and MI-type Al-Cu-Ru-Si 1/1-approximants. The pseudogap in the former is proved to originate from the interaction of electronic states with the Brillouin zone planes associated with reciprocal lattice vectors matching with the Fermi sphere in the extended zone scheme. In the latter, the Fermi surface-Brillouin zone interaction coupled with the hybridization effect between the Al-3p and transition metal d-states produces a deep pseudogap at the Fermi level. The real-space charge distribution for electrons at the Fermi level is calculated for the Al-Cu-Ru-Si 1/1-approximant. The charge distribution thus obtained could explain not only the possession of a large resistivity of this approximant but also evidenced that the icosahedral clusters play a key role in reducing the electronic energy in favor of quasicrystalline and approximant phases.

We have measured in this experiment the XPS (x-ray photoemission spectroscopy) and SXES (soft x-ray emission spectroscopy) valence spectra, the electrical resistivity, the Hall coefficient and the Rietveld structural analysis for a series of the RT-type (Rhombic Triacontahedron) Al60-xMg40Xx (X = Zn, Cu, Ag and Pd; x = 5 - 40) 1/1-approximants. The electrical resistivity at 300 K is successfully analyzed in terms of the carrier concentration per atom e/a and the ratio of the lattice constant over the “ideal” lattice constant defined as LCR. The latter is chosen as a quantitative measure of the degree of the hybridization between Al and transition metal elements Cu, Ag and Pd. We show that a sharp resistivity increase with increasing the concentration of the transition metal element can be attributed to the deepening of the pseudogap at the Fermi level, which is brought about by the combination of the Fermi surface-Brillouin zone interaction and the growth of the hybridization effect.

By combining the powdered x-ray Rietveld analysis and the High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM), we have made the detailed structural analysis for the Mackay-type Al55Si7Cu25.5Fe12.5, 1/1-cubic approximant. Electron diffraction measurements revealed its space group to be Pni3. Both position and occupancy in every atomic site are refined by means of the Rietveld analysis. The factors Rwp and Riwhich are taken as measures for the precision of the Rietveld analysis, are reduced to 2.57 and 3.89 %, respectively. The refined structure of this approximant is a simple cubic with the lattice constant of 12.31916(2) Å. Two different icosahedral clusters consisting of triply stacked atomic shells exist at the vertex and body centered positions in the CsCl-type unit cell. In addition, we propose that there exists most likely a “structural disorder” in the first shell of the cluster in one of the sublattices. The HAADF images taken along [100] and [111] directions agree with the projection images calculated from the Rietveld-refined structure, lending a strong support to the validity of the present atomic structure model deduced from the Rietveld analysis.

A combination of Si and transition metal element like V, Ni and Au can form an amorphous phase over a wide composition range. Extensive studies have been reported in relation to a change in the electron transport properties across the metal-insulator transition. It has been reported that the metal-insulator transition in the amorphous Si100−xVx alloys accompanies a substantial change in both the electronic structure and atomic structure around x=18, as revealed by the photoemission spectroscopy and neutron diffraction experiments[1]. It is of great interest to examine the structural change associated with the metal-insulator transition at an atomic level by utilizing the HRTEM[2]. However, the correspondence between the image contrast and projection of atomic structures in amorphous materials is usually indirect due to the well-known phenomena of phase contrast in HRTEM. High-angle detection annular dark field scanning transmission electron microscopy (HAADF-STEM) as illustrated in Fig.1 is a solution of the problem without contrast reversal due to the lens-defocus and thickness-variation of samples.