Systematic ion substitution has been performed on the Co site in the rock-salt (RS)-type [Ca 2 CoO 3 ] subsystem of misfit-layered cobalt oxide [Ca 2 (Co 1-x A x )O 3-delta ] 0.62 CoO 2 (A = Nb, Ru, Ta, Pb, W, La an...
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Systematic ion substitution has been performed on the Co site in the rock-salt (RS)-type [Ca 2 CoO 3 ] subsystem of misfit-layered cobalt oxide [Ca 2 (Co 1-x A x )O 3-delta ] 0.62 CoO 2 (A = Nb, Ru, Ta, Pb, W, La and Zr). The oxygen deficiency delta and the decomposition temperature T d of the substituted samples have been determined by means of the thermogravimetric analysis (TGA). Upon heating, the oxygen atoms are gradually released from the RS-type subsystem up to delta~0.10. A small amount (x = 0.10) of the substitution remarkably increases T d from 1173 K (x = 0) up to 1246 K (A = Nb). The Pb-substituted samples show substantial decrease in electrical resistivity p from 19.2 mOmegacm to 13.8 mOmegacm (x = 0.10) at 950 K. The highest thermoelectric power, S 2 p -1 = 2.1times10 -4 WK -2 m -1 , is realized for the Pb-substituted sample with x = 0.10 at 950 K
Several theories and program codes were developed for large-scale atomistic simulations with fully quantum mechanical description of electron systems. The fundamental concepts are generalized Wannier state and Krylov ...
Several theories and program codes were developed for large-scale atomistic simulations with fully quantum mechanical description of electron systems. The fundamental concepts are generalized Wannier state and Krylov subspace. Test calculations were carried out with upto 106 atoms using a standard workstation. How electronic state is described in large-scale calculation was demonstrated on Si(001)-(2×1) surface. As a practical application, cleavage fracture of silicon was simulated with 10-nm-scale samples for investigating its nanoscale mechanical behavior. Discussions are focused on the unstable (001) cleavage mode and the stable (experimentally observed) (111)-(2×1) cleavage mode. As well as elementary surface reconstruction, step formation and bending in cleavage path were observed. These results were compared with experiments, such as scanning tunneling microscope (STM).
Recently a long distance and high key rate quantum key distribution (QKD) has become possible by the idea of the decoy state method. We show that a longer distance QKD is possible by utilizing a heralded single photon...
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Recently a long distance and high key rate quantum key distribution (QKD) has become possible by the idea of the decoy state method. We show that a longer distance QKD is possible by utilizing a heralded single photon source (utilizing spontaneous parametric down-conversion) as a source instead of a weak coherent pulse (WCP) as proposed in the original decoy state method. Moreover, the key rate is improved by utilizing a presently available photon number resolving detector as a trigger detector of the heralded single photon source and it is shown to approach the key rate of the WCP.
A linear algebraic method named the shifted conjugate-orthogonal conjugate-gradient method is introduced for large-scale electronic structure calculation. The method gives an iterative solver algorithm of the Green’s...
A linear algebraic method named the shifted conjugate-orthogonal conjugate-gradient method is introduced for large-scale electronic structure calculation. The method gives an iterative solver algorithm of the Green’s function and the density matrix without calculating eigenstates. The problem is reduced to independent linear equations at many energy points and the calculation is actually carried out only for a single energy point. The method is robust against the round-off error and the calculation can reach the machine accuracy. With the observation of residual vectors, the accuracy can be controlled, microscopically, independently for each element of the Green’s function, and dynamically, at each step in dynamical simulations. The method is applied to both a semiconductor and a metal.
The electronic structure of A-type antiferromagnetic insulator LaMnO3 is investigated by the GW approximation. The band gap and spectrum are in a good agreement with experimental observation. The lifetime of electrons...
The electronic structure of A-type antiferromagnetic insulator LaMnO3 is investigated by the GW approximation. The band gap and spectrum are in a good agreement with experimental observation. The lifetime of electrons in conduction bands is much shorter than that of holes in valence bands. The insulator-to-metal transition with antiferromagnetic-to-ferromagnetic transition with photocarrier injection is attributed to the characteristic properties of excited electron states in A-type antiferromagnetic perovskite systems. The onsite d−d Coulomb interaction is strongly screened at the low energy region by mobile eg electrons.
We report that Ce doping was achieved in La2CuO4 with the K2NiF4(T) structure for the first time by molecular beam epitaxy. A synthesis temperature of as low as ∼ 630°C and an appropriate substrate choice, i.e.,...
We report that Ce doping was achieved in La2CuO4 with the K2NiF4(T) structure for the first time by molecular beam epitaxy. A synthesis temperature of as low as ∼ 630°C and an appropriate substrate choice, i.e., (001)LaSrGaO4(as=3.843Å), enabled us to incorporate Ce into the K2NiF4 lattice and to obtain Ce-doped T−La2−xCexCuO4 up to x∼0.06. The doping of Ce makes T−La2CuO4 more insulating, which is in sharp contrast to Sr (or Ba) doping in T−La2CuO4, which makes the compound metallic and superconducting. The observed smooth increase in resistivity from the hole-doped side (T−La2−xSrxCuO4) to the electron-doped side (T−La2−xCexCuO4) indicates that the electron-hole symmetry is broken in the T-phase materials.
We developed a pressure-driven flow control system for chemical reaction in nanochannel. In this system, back pressure regulating was utilized to prevent the high pressure loss, which is usually occured in nanochannel...
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Recently, we have reported the synthesis of phenol-furfural (or formaldehyde) polymer nanotubes in the presence of cationic surfactant as the template. But it was unsuccessful to apply these nanotubes to proton conduc...
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Recently, we have reported the synthesis of phenol-furfural (or formaldehyde) polymer nanotubes in the presence of cationic surfactant as the template. But it was unsuccessful to apply these nanotubes to proton conductors and carbon precursors, due to chemical and thermal instability of their frameworks. Here we report the synthesis of nanostructural polymer materials through resorcinol-formaldehyde copolymerization in the presence of CnTAB (n=16, 18).
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