The electronic structures are calculated for several crystalline approximants of quasicrystals, AlCuLi and AlFe. The densities of states of these systems, and also of AIMn, suggest universality of the pseudogap at the Fermi energy in quasicrystals. The pseudogap satisfies a Hume-Rothery-type relation. The origin of the pseudogap is attributed to strong electron scattering by the lattice and the pseudogap causes an enhancement of cohesive energies. The characteristics of the states in the pseudogap and the electric resistivity are also discussed.PACS numbers: 65.40.Em, Since the discovery of quasicrystals, 1,2 theoretical investigations have focused mainly on their structures and phasons. Recently, the electronic properties have received much attention. The main interest is twofold: One is electronic transport or localization 3 " 5 and the other is the electronic mechanism of cohesion. 6 " 9 The diffraction pattern in quasicrystals is a sum of densely distributed 8 functions with crystallographically disallowed orientational symmetry. The anomalous diffraction pattern suggests that electrons in quasicrystals may be always and everywhere scattered strongly and the electron wave functions oscillate at all scales. This is the case in the one-dimensional Fibonacci lattice and the energy spectrum has gaps at almost every energy value. 3 In the two-dimensional case, the situation is not essentially changed. The energy spectrum of the twodimensional Penrose lattice is not smooth and most of the wave functions are critical, i.e., neither extended nor exponentially localized, and presumably with power-law decay. 4 Recently, high quality samples of stable quasicrystals with only small amounts of structural disorder and phasonlike defects were prepared, and their electric resistivity has been observed to be anomalously large. The electric resistivity in icosahedral AlCuLi is 6 times larger than in crystals, whereas the coefficient of the linear-temperature-dependent term of the specific heat is almost the same in two phases. 10 The electric resistivity of stable icosahedral AlCuRu has been observed to increase drastically, up to 2500 p. Cl cm or more at 4.2 K. 11 Therefore, we presume that electronic states in threedimensional quasicrystals are also critical. The anomalous diffraction pattern also suggests a strong electronlattice interaction and one may expect it has a crucial role for stability, such as in the Hume-Rothery or Peierls mechanism.In this paper, we present the electronic structures of crystalline approximants of realistic quasicrystals, AlCu-Li and AlFe, and discuss an electronic mechanism of cohesion and stability in realistic quasicrystals. Discussions are concerned with R-AlCuLi and Alj 4 Fe3, together with a-AlMn. 8 These are the crystalline approximants of typical quasicrystals: the stable icosahedral quasicrystal /-AlCuLi, the metastable icosahedral quasicrystal /-AlMnSi, and the metastable decagonal quasicrystal rf-AlFe. The crystalline phase of AlCuLi, i.e., /^-AlCuLi, reveals the typical structure of...

In a binary mixture of oligomers of styrene and f-caprolactone, we have studied a transition from metastability to instability by changing a quench depth systematically under an off-critical quench condition. The concentration distribution function turns out to be a good fingerprint for determining whether phase separation is nucleation-growth type or spinodal-decomposition type. We also demonstrate clear morphological and kinetic evidence of a diffuse metastable-unstable transition or crossover phenomena theoretically predicted for the system with a finite-range interaction.

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