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Hideo Kishida

Publications and source records attributed to Hideo Kishida.

8 recordsLinked to original sources
PubMed2006

Dynamical valence fluctuation at the charge-density-wave phase boundary in iodide-bridged Pt compound [Pt(chxn)2I]I2.

We synthesized a novel iodo-bridged linear chain platinum compound, having the quasi-two-dimensional charge-density-wave (CDW) ground state and the smallest band gap. In this compound, we discovered an anomalous valence state in the boundary region at which the CDW phase alternates in the crystal by means of ESR, X-ray diffuse scattering, STM, and electrical resistivity. This anomalous state can be explained by the fast fluctuation between Pt(IV)-I...Pt(II) and Pt(II)...I-Pt(IV) in the double well potential. This is the first observation of the dynamical fluctuation of the CDW phase among the quasi one-dimensional halogen-bridged complexes.

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PubMed2003

Carrier doping effect into quasi-one-dimensional bromo-bridged Ni(III) complexes with strong electron-correlation by Cu(II) ions, [Ni1-xCux(chxn)2Br]Br2-x.

This communication will describe the electron doping effect into Ni(III) complexes by Cu(II) ions, [Ni(1-x)Cu(x)(chxn)(2)Br]Br(2-x) (x = 0.038 and 0.101) by using an electrochemical oxidation method. A drastic increase of electrical conductivity as well as a new absorption band around 0.5 eV in single crystal reflectance spectra was observed by doping Cu(II) ions, indicating the electron doping was successfully made. An ESR result shows unpaired electrons locate in the d(x2-y2) orbitals of Cu(II) and have almost no interaction with those of other ions.

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PubMed2003

Novel ET-coordinated copper(I) complexes: syntheses, structures, and physical properties (ET = BEDT-TTF = Bis(ethylenedithio)tetrathiafulvalene).

New molecular charge-transfer complexes of bis(ethylenedithio)tetrathiafulvalene (ET), (ET)Cu(2)Br(4) (1), (ET)(2)Cu(6)Br(10) (2), (ET)(2)[Cu(4)Br(6)ET] (3), (ET)(2)Cu(2)Br(4) (4), (ET)(2)Cu(3)Br(7)(H(2)O) (5), and (ET)(2)Cu(6)Br(10)(H(2)O)(2) (6), have been synthesized by diffusing reaction of ET and Cu(II)Br(2). Their crystal structures and physical properties have been investigated. X-ray analyses revealed that ET molecules coordinated to the copper ions with the sulfur atoms of the ethylenedithio groups in all compounds. The Cu-S distances are found in the range 2.268(5)-2.417(8) A, being close to the typical Cu(I)-S coordination bond distances. Strong d-pi interactions between d-electrons of the copper ions and pi-electrons of the ET molecules can be expected through the Cu-S coordination bonds. ET molecules behave as trans-bidentate ligands bonding to two different copper ions in 1 and 3, as cis-bidentate ligands in 2, 5, and 6, and as monodentate ligands in 4. In the crystal structure of 3, there are two types of ET molecules in the crystal structure, where the first type is a trans-bidentate ligand and the second forms a stacking structure by itself. Compounds 1, 2, 4, and 6 show semiconducting behavior down to low temperature (sigma(RT) = 1.6 x 10(-2) S cm(-1) and E(a) = 122 meV for 1, sigma(RT) = 2.1 S cm(-1) and E(a) = 21 meV for 2, sigma(RT) = 5.4 x 10(-4) S cm(-1) and E(a) = 239 meV for 4, and sigma(RT) = 5.1 x 10(-2) S cm(-1) and E(a) = 207 meV for 6). On the other hand, in 3, a metal-like region is observed along the b-axis and c-axis, due to the contribution of stacked ET molecules, and a metal-semiconductor transition occurs at 280 and 270 K, respectively. Also, 5 exhibits metallic conductivity in the temperature ranges 240-300 and 200-300 K along the b-axis and c-axis, respectively, despite the oxidation state of ET with 2+.

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PubMed2002

Tuning of spin density wave strengths in quasi-one-dimensional mixed-halogen-bridged nickel(III) complexes with strong electron correlation, [Ni(III)(chxn)(2)Cl(1-x)Br(x)](NO(3))(2).

This communication describes the syntheses of the quasi-one-dimensional mixed-halogen-bridged Ni(III) complexes with strong electron correlation [Ni(chxn)(2)Cl(1-x)Br(x)](NO(3))(2) and the tuning of the spin density wave strengths of these compounds. If the Cl 3p and Br 4p make one band in the compounds, we should observe a single peak in the electronic spectra. As a result, we should observe the single peak from 1.45 to 2.00 eV depending on the mixing ratios of Cl and Br ions. Therefore, the Cl 3p and Br 4p make one band. Then, we have succeeded in tuning the spin density wave strengths of the Ni(III) complexes with the strong electron correlation by mixing the bridging halogen ions successively.

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PubMed2002

Angle-resolved photoemission study of the MX-chain compound [Ni(chxn)(2)Br]Br(2): spin-charge separation in hybridized d-p chains.

We report on the results of angle-resolved photoemission experiments on a quasi-one-dimensional (1D) MX-chain compound [Ni(chxn)2Br]Br2, which shows a gigantic nonlinear optical effect. A "band" having about 500 meV energy dispersion is found in the first half of the Brillouin zone, but disappears at kb/pi approximately 1/2. These spectral features are well reproduced by the d-p chain model with a small charge-transfer energy Delta compared with that of 1D Cu-O compounds. We propose that this smaller Delta is the origin of the absence of clear spin-charge separation in the photoemission spectra and the strong nonlinear optical effect.

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