Norimichi Kojima

Synthesis of Triaxial LiFePO4 Nanowire with a VGCF Core Column and a Carbon Shell through the Electrospinning Method

A triaxial LiFePO4 nanowire with a multi wall carbon nanotube (VGCF:Vapor-grown carbon fiber) core column and an outer shell of amorphous carbon was successfully synthesized through the electrospinning method. The carbon nanotube core oriented in the direction of the wire played an important role in the conduction of electrons during the charge-discharge process, whereas the outer amorphous carbon shell suppressed the oxidation of Fe2+. An electrode with uniformly dispersed carbon and active materials was easily fabricated via a single process by heating after the electrospinning method is applied. Mossbauer spectroscopy for the nanowire showed a broadening of the line width, indicating a disordered coordination environment of the Fe ion near the surface. The electrospinning method was proven to be suitable for the fabrication of a triaxial nanostructure.

Electrochemical Mg2+ intercalation into a bimetallic CuFe Prussian blue analog in aqueous electrolytes

Mg2+ intercalation/deintercalation is achieved by using aqueous electrolytes and Prussian blue analog electrodes. Ex situ X-ray diffraction evidenced the solid solution process of Mg2+ intercalation/deintercalation, while the 57Fe Mossbauer spectroscopy and X-ray absorption near edge structure revealed redox of both Cu and Fe.

Control of charge transfer phase transition and ferromagnetism by photoisomerization of spiropyran for an organic-inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)3] (SP = spiropyran, dto = C2O2S2).

Iron mixed-valence complex, (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)](dto = C(2)O(2)S(2)), shows a spin entropy-driven phase transition called charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) around 120 K and a ferromagnetic transition at 7 K. These phase transitions remarkably depend on the hexagonal ring size in the two-dimensional honeycomb network structure of [Fe(II)Fe(III)(dto)(3)](-)(infinity). In order to control the magnetic properties and the electronic state in the dto-bridged iron mixed-valence system by means of photoirradiation, we have synthesized a photosensitive organic-inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)(3)](SP = spiropyran), and investigated the photoinduced effect on the magnetic properties. Upon UV irradiation at 350 nm, a broad absorption band between 500 and 600 nm appears and continuously increases with the photoirradiation time, which implies that the UV irradiation changes the structure of spiropyran from the closed form to the open one in solid state. The photochromism in spiropyran changes the ferromagnetic transition temperature from 5 to 22 K and the coercive force from 1400 to 6000 Oe at 2 K. In this process, the concerted phenomenon coupled with the charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) and the photoisomerization of spiropyran is realized.

Ferromagnetic exchange couplings showing a chemical trend in Cu-Ln-Cu complexes (Ln = Gd, Tb, Dy, Ho, Er).

Exchange couplings in isomorphous [LnCu(2)] were evaluated by high-frequency electron paramagnetic resonance and magnetization studies. The exchange parameter J(Ln-Cu) was decreased with an increase in the atomic number; J(Ln-Cu)/k(B) = 4.45(11), 2.27(6), 0.902(10), 0.334(3), and 0.136(8) K for Ln = Gd, Tb, Dy, Ho, and Er, respectively.

Reversible charge-transfer phase transition in [(n-C3H7)4N][FeIIFeIII(dto)3](dto = C2O2S2)

We have investigated the physical properties of [(n-C 3 H 7 ) 4 N][Fe II Fe III (dto) 3 ](dto = C 2 O 2 S 2 ) by means of 57 Fe Mossbauer spectroscopy, ESR, and magnetic susceptibility. From the analysis of 57 Fe Mossbauer spectra, we have discovered a new type of first order phase transition for the title complex at about 120 K, where the charge transfer transition between Fe II and Fe III occurs reversibly. Moreover, we have found the ferromagnetic phase transition at 6 K.

Photo-Induced Absorption Band in One-Dimensional Halogen-Bridged Mixed-Valence Platinum Complex: [Pt(en)2][PtI2(en)2](SO4)2·6H2O and its Au-Doped Complex: [AuxPt1-xI(en)2]SO4·3H2O

The intervalence charge-transfer absorption spectra in the mixed-valence complexes [Pt(en) 2 ][PtI 2 (en) 2 ](SO 4 ) 2 ·6H 2 O and [Au x Pt 1- x I(en) 2 ]SO 4 ·3H 2 O ( x =0.03) have been investigated at 4.2 K. In these complexes, below the charge-transfer absorption edge, a weak absorption band ( A -band) has been observed for the light polarized parallel to the chain axis. When these complexes were irradiated with the light in the region of the charge-transfer transition from Pt II to Pt IV , the absorption coefficient of the A -band increased remarkably, which implies that the A -band is a photo-induced absorption band. The photo-induced effect for the A -band in [Au x Pt 1- x I(en) 2 ]SO 4 ·3H 2 O ( x =0.03) is more intense than that in [Pt(en) 2 ][PtI 2 (en) 2 ](SO 4 ) 2 ·6H 2 O. The A -band suggests the existence of new excitations such as a soliton-like excitation in the electronic state of the platinum chains.

Reversible solid state redox of an octacyanometallate-bridged coordination polymer by electrochemical ion insertion/extraction.

Coordination polymers have significant potential for new functionality paradigms due to the intrinsic tunability of both their electronic and structural properties. In particular, octacyanometallate-bridged coordination polymers have the extended structural and magnetic diversity to achieve novel functionalities. We demonstrate that [Mn(H2O)][Mn(HCOO)(2/3)(H2O)(2/3)](3/4)[Mo(CN)8]·H2O can exhibit electrochemical alkali-ion insertion/extraction with high durability. The high durability is explained by the small lattice change of less than 1% during the reaction, as evidenced by ex situ X-ray diffraction analysis. The ex situ X-ray absorption spectroscopy revealed reversible redox of the octacyanometallate. Furthermore, the solid state redox of the paramagnetic [Mo(V)(CN)8](3-)/diamagnetic[Mo(IV)(CN)8](4-) couple realizes magnetic switching.

On-off optical switching of the magnetic and structural properties in a spin-crossover complex

A photoexcitation is one of the promising external fields to control the material phases. Here, the authors have demonstrated that the magnetic and structural properties of a spin-crossover complex, Fe(phen)2(NCS)2 (phen=1,10-phenanthroline), can be reversibly switched by the on-off action of the continuous photoexcitation at the same temperature. The structural data suggest that the density of the high-spin Fe2+ in the photoinduced phase is about 0.88. Suppressed atomic vibrations of the photoinduced phase exclude the conventional heating effect as the origin for the observed optical switching.

Strcutural Analysis of [Fe(ptz)6)](BF4)2 under Photo-Excitation –Condensation of Photo-Excited High-Spin Ions–

We have performed in situ synchrotron-radiation X-ray powder structural analysis in a spin-crossover complex ([Fe(ptz) 6 )](BF 4 ) 2 : ptz = propyltetrazole) under a photo-excitation with a continu...

Magnetic properties of an organic spin-ladder compound (BEDT-TTF)Zn(SCN)3

Abstract The title compound (BEDT-TTF)Zn(SCN)3 is the first example of a spin-ladder with a frustrating antiferromagnetic interaction. The results of the ESR and the static magnetic susceptibility measurements are reported and discussed based on an extended-Huckel calculation. The temperature dependence of the spin susceptibility is in good agreement with the combination of about 1% of Curie component and a spin-ladder model with a spin-gap of 340 K. The existence of the spin-gap is experimentally confirmed for the first time for a spin-ladder in the weak-coupling limit. Possible effect of the frustration due to the diagonal interaction is also discussed.