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We have investigated the electronic structure of silver chalcogenides Ag2X (X = S, Se, Te) and their solid solutions using hard x-ray photoemission spectroscopy in combination with density functional theory calculations using generalized gradient approximation (GGA). By including the corrections for on-site Coulomb interactions (GGA + U), we successfully reproduced the valence band photoemission spectra, which consist mainly of the Ag 4d band, by calculation. The estimated values for U = 4–6 eV are slightly high for Ag 4d electrons but are consistent with those used in previously reported structural studies. On the other hand, the magnitude of the energy gap is virtually independent of U. These results suggest the strong correlation between Ag 4d electrons in Ag2X compounds to have surprisingly little impact on their electron transport properties. [ABSTRACT FROM AUTHOR]

We have investigated the electronic structure of a potential thermoelectric material, higher manganese silicide, and its solid solutions with supersaturated Re by means of hard x-ray photoemission spectroscopy. The unusual Re substitution dependence of thermoelectric properties in the higher manganese silicide, reducing the electrical resistivity without altering the Seebeck coefficient, can be explained in terms of the variation of the density of states at the Fermi level and its energy derivative. Such an electronic structure variation contributes to an improvement in the thermoelectric performance in combination with the suppressed thermal conductivity. [ABSTRACT FROM AUTHOR]

In order to develop practical thermoelectric materials consisting solely of environmentally friendly elements, we investigated the thermoelectric properties of the AlMn-type ( P6/ mmc, hp26) AlMnSi alloys and the AlMnSi-type ( Pm-3, cP138) AlMnFeSi alloys, both of which possess a pseudogap at the Fermi level. The formation range in which the single phase is obtained was determined for these two phases. The electrical resistivity, Seebeck coefficient, and thermal conductivity of the samples involving no secondary phase were measured over the temperature range of 2 K to 300 K. It is found that the thermoelectric properties of these phases are qualitatively accounted for in terms of the pseudogap at the Fermi level in the electronic density of states and the disordering in local atomic arrangements. [ABSTRACT FROM AUTHOR]

The density of states (DOS) of the conduction and valence bands of a single quasicrystal of Al72NI20Co8 were obtained using electron energy-loss spectroscopy and X-ray emission spectroscopy based on transmission electron microscopy. A complete DOS near the Fermi level, which shows a clear pseudo-gap structure compared to that of aluminium, is presented for the first time. The DOS distribution is non-symmetric about the Fermi level. Onset energies of Al L-shell excitation spectra of amorphous, quasicrystalline and crystalline Al75Cu15V10 are compared with that of aluminium. Only that of the quasicrystalline phase shows a shift to the higher energy side by 0.3 eV. Onset energies of Al L-shell excitation spectra of Al-based quasicrystals (Al73Co27, Al63Cu25Fe12, Al63Cu25Ru12 and Al70Pd20Mn10) and corresponding approximant crystals are compared with that of aluminium. The onset energies of these quasicrystals show chemical shifts to the high energy side, indicating a smaller amount of valence charge at Al atom sites in the quasicrystalline phase than that of aluminium. Onset energies of approximant crystals of τ0,τ2-Al73Co27, Al55Cu25Fe12Si8, Al55Cu25Ru12Si8 do not show a shift, and 1/1-Al67Pd11Mn14Si8 and 2/1-Al70Pd23Mn6Si1 show shifts compared with that of aluminium. An amount of the chemical shift of 2/1-Al70Pd23Mn6Si1 is larger than that of 1/1-Al67Pd11Mn14Si8. The results show that a decrease of valence charge at Al sites is characteristic for Al-based quasicrystalline materials. It may be attributed to an increase of covalency in the bonding of the quasicrystalline materials. [ABSTRACT FROM AUTHOR]

Valence band spectra of icosahedral quasicrystals and their 1/1 cubic approximants in the Cd-Yb and Cd-Ca systems are investigated systematically. A sharp Fermi edge, indicative of sizable density of states at the Fermi level ( E F ), is clearly observed for all the compounds and E F is located not at the bottom of the pseudogap but at its shoulder. In addition, a peak structure appears just below E F for the Cd-Ca system, which is also found for the Cd-Yb system when subtracting a Yb 4f derived doublet. Ca 2p-3d resonant photoemission spectroscopies on the Cd-Ca compounds reveal the existence of Ca 3d states at E F , indicating that the 3d states do contribute to the peak structure at E F , which is attributed to hybridization with the Cd sp states. The low-temperature structural properties of the Cd-based compounds are also reported. An occurrence of a structural phase transition at 110?K and 100?K for Cd 6 Yb and Cd 6 Ca, respectively, is well documented. The transitions are understood as a consequence of an orientational ordering of Cd 4 tetrahedron located at the center of the icosahedral clusters. It is suggested that two orientations of the Cd 4 tetrahedron alternatively occur along the [110] direction of the high temperature bcc phase. [ABSTRACT FROM AUTHOR]

The electronic structures of Ce compounds have been investigated by means of resonant soft X-ray emission spectroscopy (RXES) excited at resonant energy range of Ce 3d → 4f absorption. Polarization dependence of the RXES shows information on concerning electronic states. In CeO[sub 2], the Ce 4f → 3d RXES spectra are interpreted as electronic structures hybridized between 4f[sup 0] and 4f¹v states. Peaks appearing in the spectra are attributed to bonding, nonbonding, and antibonding states between those states, while the spectra of CeRh[sub 3] cannot be explained by only using the hybridization between 4f[sup 0] and 4f¹v states. The spectra have large broad Raman peak, especially when the excitation photon energy is set at satellite of Ce 3d → 4f absorption. We attribute the origin of the broad Raman peak to hybridization states involving electron-hole pairs. [ABSTRACT FROM AUTHOR]

We have performed soft X-ray emission (SXE) and high-resolution photoemission (PE) spectroscopy to study the electronic structures of β-HfNCl and Na-intercalated HfNCl. Both the PE and SXE spectra of Na0.37HfNCl show an additional structure within the band gap of β-HfNCl, without an apparent shift in the energy position of valence-band features. These results clearly reveal intercalant-induced changes in the electronic structure of the layered nitride chlorides. From these results, we propose non-rigid band like behavior for this system in contrast to generally expected rigid-band filling upon intercalation. [Copyright &y& Elsevier]

Abstract: The electronic structure and phase stability of the Zr66.7Ni33.3 and Zr66.7Cu33.3 metallic glasses has been investigated by the recursion calculations method using a giant atom-cluster, of which arrangements of constituent atoms were determined by the Reverse Monte Carlo experimental structural studies reported before [T. Fukunaga, K. Itoh, T. Otomo, K. Mori, M. Sugiyama, H. Kato, M. Hasegawa, A. Hirata, Y. Hirotsu, Intermetallics 14 (2006) 893]. The electronic structure of the former is similar to that of the relevant Zr2Ni compound, while that of the latter is completely different from that of the relevant Zr2Cu compound. We have also calculated the band energy of the characteristic clusters in these metallic glasses. The smaller and Zr-richer these clusters are, the lower the band energy at the center of the cluster tends to be. The stability of these characteristic clusters of both metallic glasses can be explained by the total band energy based on the calculated local density of states and is consistent with the reported experimental Volonoi analysis. [Copyright &y& Elsevier]

EuCo 2 Ge 2 with the tetragonal structure is a Eu-divalent antiferromagnet with the Néel temperature T N = 23 K. The magnetic easy-axis corresponds to the [100] direction ( a -axis), while the [001] direction ( c -axis) is a hard-axis. The magnetization for H ∥ [ 100 ] indicates a metamagnetic transition at 25 kOe and saturates above 75 kOe. On the other hand, the hard-axis magnetization increases approximately linearly and saturates above 110 kOe. The magnetic phase diagram was constructed. A characteristic feature in EuCo 2 Ge 2 is known as a valence transition under pressure, from Eu 2 + δ to Eu 3 − δ ′ ( δ , δ ′ < 1 ). We also clarified the valence transition by measuring the electrical resistivity under pressure. The valence transition occurs at 3 GPa, with a hysteresis, and terminates at about 4.5 GPa. Further increasing pressure, the electronic state is changed into a moderate heavy fermion state and approaches the nearly trivalent electronic state. [ABSTRACT FROM AUTHOR]

Abstract: We report high-resolution angle-resolved photoemission spectroscopy on single-layered cuprate superconductor (Bi,Pb)2(Sr,La)2CuO6+δ as a function of temperature and doping level, to elucidate the origin of shadow band (SB). We found that the intensity of SB is invariable with respect to temperature, doping, and substitution constituents of block layers, indicating that antiferromagnetic correlation is not responsible for the emergence of SB. Observation of similar SB in Bi2Sr2CaCu2O8+δ and La1.85Sr0.15CuO4, but not in YBa2Cu3O7−δ further supports the structural origin of SB. [Copyright &y& Elsevier]

Abstract: The electronic structure of the Zr-based metallic glasses has been investigated by theoretical and experimental approaches. One approach is band calculations of the Zr2Ni (Zr66.7Ni33.3) compound to investigate the electronic structure of the Zr66.7Ni33.3 metallic glass (ΔT x =0K) of which the local atomic structure is similar to that of the Zr2Ni compound. The other is photoemission spectroscopy of the Zr50Cu35Al15 bulk metallic glass (BMG) (ΔT x =69K). Here ΔT x = T x − T g where T x and T g are crystallization and glass transition temperature, respectively. Both results and previous ones on the Zr55Cu30Ni5Al10 BMG indicate that there is a pseudogap at the Fermi level in the electronic structure of these Zr-based metallic glasses, independent of the value of the ΔT x. This implies that the pseudogap at the Fermi level is one of the factors that stabilize the glass phase of Zr-based metallic glasses. [Copyright &y& Elsevier]

Abstract: The electronic structure of a bulk metallic glass Zr55Al10Cu30Ni5 has been studied by means of photoelectron spectroscopy in order to understand the origins of its large glass formation ability and unique mechanical properties from the microscopic point of view. The valence-band photoelectron spectra show three bands ascribed to the Zr 4d, Ni 3d, and Cu 3d states. A remarkable feature of these bands is the highly symmetric spectral shape with the high-binding energy and narrow width in comparison with the d bands of the crystalline transition metals. This is attributed to the lack of the crystalline periodicity in the metallic glass as well as the reduction in the neighbouring atoms to hybridize with those transition metals. A high-resolution valence-band spectrum also reveals the intensity reduction near the Fermi level, which implies that the pseudo-gap in the electronic structure may be one of the important factors for the glass formation. [Copyright &y& Elsevier]

Soft X-ray absorption (XAS) spectra and their magnetic circular dichroism (MCD) have been studied at the transition-metal L2,3 thresholds of Heusler-type Fe2-xV1+xAl intermetallic compounds. Satellite structures 5 eV above the main Fe and V L2,3 XAS peaks are attributed to a singularity in the density of states, and fine structures in the V L2,3 spectra is ascribed to the multiplets. Observed MCD intensity changes as the bulk magnetization on changing the content x in Fe2-xV1+xAl. Although the observed MCD signals are small, they definitely indicate the anti-ferromagnetic coupling between the Fe and V magnetic moments, as predicted for the magnetic cluster formed around the anti-site defects in the Heusler lattice. The existence of the magnetic cluster may cause the unusual transport properties at low temperatures. [Copyright &y& Elsevier]

We study the electronic structure of Tsai-type cluster-based quasicrystalline approximants, Au64 Ge22 Yb14 (AGY-I), Au63.5 Ge20.5 Yb16 (AGY-II), and Zn85.4 Yb14.6 (Zn-Yb), by means of photoemission spectroscopy. In the valence band hard x-ray photoemission spectra of AGY-II and Zn-Yb, we separately observe a fully occupied Yb 4f state and a valence fluctuation derived Kondo resonance peak, reflecting two inequivalent Yb sites, a single Yb atom in the cluster center and its surrounding Yb icosahedron, respectively. The fully occupied 4f signal is absent in AGY-I containing no Yb atom in the cluster center. The results provide direct evidence for a heterogeneous valence state in AGY-II and Zn-Yb. [ABSTRACT FROM AUTHOR]