Tomochika Matsuyama

Mossbauer Spectroscopic Study of Iodine-Doped Polyacetylene

The Mossbauer spectroscopy has been applied to iodine-doped polyacetylene employing 129 I. It is found that the polymer films contain I - , I 3 - and I 5 - with symmetrical charge population, where the content of each iodide anion depends on the doping level. Under dynamic evacuation, it is elucidated that I 5 - converts to I 3 - by the elimination of I 2 from I 5 - . The variation of electrical conductivity in iodine-doped polyacetylene is discussed with the mechanism of charge transfer from the polymer and with the mutual conversion of iodide anions.

Mossbauer study of polythiophene and its derivatives

Summary form only given. Polythiophene and its derivatives are highly conducting polymers when doped with appropriate chemical species such as iodine or FeCl/sub 3/. We have investigated the chemical structure of the dopants in these polymers using / sup 129/I and /sup 57/Fe, which are Mossbauer nuclei of good resolution. It has been found that the iodine in these polymers exists as linear forms of triiodide and pentaiodide anions and that the abundance ratio of triiodide decreases with increasing of the doping level. Since the polymers were doped with the iodine of neutral molecules, these anions are created by electron transfer between the polymers and the dopants. Our experimental results are consistent with the proposed mechanism of the electric conductivity which is due to migration of polarons on the polymer chains.

An 129I Mössbauer spectroscopic study of iodine doped in poly(vinylpyridines)

The charge densities and the configurations of iodine doped in poly(2‐ and 4‐vinylpyridines) have been studied by using the Mossbauer effect of 129I at 16 K. The ’’outer complex’’ is first formed in the system of poly(2‐vinylpyridine) and iodine. The extent of the charge transfer is estimated to be 0.22 in the outer complex, which is nearly the same as pure pyridine. The iodine of the outer complex varies gradually to the tri‐iodide anion and then to the iodide anion by accepting electrons from the pyridine ring of the polymer. In the system of poly(4‐vinylpyridine) and iodine both the outer complex and the ’’inner complex’’ are first observed, and the iodine species in these complexes vary gradually to the I3− ion and finally to the I− ion in a similar manner as the system of poly(2‐vinylpyridine) and iodine. From the values of the Mossbauer parameters the charge or electron populations of the iodine species are calculated, and the arrangements of these species are discussed.

Mössbauer spectroscopic study on polyacetylene doped with iodine

Abstract The 129 I Mossbauer effect has been applied to polyacetylene films of cis -(CHI 0.23 ) x as prepared and cis -(CHI 0.20 ) x led under dynamic evacuation. It has been clarified that both films contain linear I − 5 and I − 3 with symmetric charge population and that the fraction of I − 3 increases after evacuation. The mechanism of electrical conductivity in iodine-doped polyacetylene has been discussed on the basis of the chemical form and the dynamic behavior of the anion species.

Electrical conductivity and ESR studies in iodine-doped polythiophene from semiconductor to metallic regime

Dependences of electrical conductivity and ESR of iodine-doped polythiophene films, (C 4 H 2 SI y ) x , on iodine concentrations which are precisely determined by a neutron activation technique (from a dilute level of y ∼4×10 -4 to a deep level of y ∼4×10 -1 ) are reported. A drastic increase of conductivity from 10 -8 to 10 -2 S/cm is observed at the fairly narrow dopant concentration region of 2×10 3 < y <5×10 -3 , accompanied by a remarkable decrease in the activation energy of conductivity. At this transitional region, the ESR signal also changes significantly, showing a maximum spin density and a minimum linewidth. These results are discussed to understand the semiconductor-to-metal transition in iodine-doped polythiophene, taking polaron and bipolaron models into account.

Utilization of coherent transition radiation from a linear accelerator as a source of millimeter-wave spectroscopy

A spectroscopic system for the millimeter-wave region has been constructed on the coherent radiation beamline at the KURRI-LINAC of the research reactor institute, Kyoto University. Coherent transition radiation has been used as the light source. The observed spectrum of radiation was distributed throughout the entire millimeter-wave region and the intensity was four orders of magnitude larger than that of the conventional light source which has the continuous spectrum, i.e., a mercury-arc lamp. The interference between wave packets emitted from successive bunches was observed. It showed that the spectrum of coherent transition radiation was constituted of the higher harmonics of the L-band radio frequency (1.3 GHz) and that the high resolution spectrum was not a continuous spectrum. The diameter of the light beam at the position of a sample was about 9 mm (full width half maximum) and it increased as the wavelength became long because of the diffraction effect for the finite sizes of the optical componen...

Metallic transport properties in electrochemically as-grown and heavily doped polythiophene and poly(3-methylthiophene)

Abstract We have studied the temperature dependence of the ordinary 4-terminal conductivity, VSC conductivity, thermoelectric power (TEP) and low-freqeuency ESR for ClO4-doped (as grown) polythiopene (PT) and poly(3-methylthiophene) (PMeT) as well as for those doped further with HClO4. Al high temperatures the VSC conducttivity changes with T−2 in the as-grown PT, whereas it changes with T−1-in the as-grown PMeT. Such a metallic behaviour with temperature was also obtained in the low-frequency ESR linewidth. Results of the TEP experiments were suggestive as well of the metallic characteristics. The temperatures results of both the VSC and the TEP measurements indicate that a metal-insulator (or semiconductor) transition takes place at 30K for PT and 10K for PMet.

Reflectivity and Electronic Structures of Layered Ionic Crystals, (CnH2n+1NH3)2CdCl4: n=1, 2, 3

The reflection spectra of (C n H 2 n +1 NH 3 ) 2 CdCl 4 were measured in the photon energy region of 0.5–25 eV at room temperature (RT) and liquid nitrogen temperature (LNT) by means of synchrotron radiation. It was found that absorption spectra of the present crystals resemble that of CdCl 2 crystals except for an additional peak at 5.10 eV (RT). The energy of the additional peak shifts with temperature by as much as 0.38 eV from 5.10 eV (RT) to 5.48 eV (LNT). This absorption peak has doublet structure and the splitting energy is 0.1 eV, which is the same magnitude as the spinorbit splitting of a chlorine atom. The band is assigned to be an electronic transition from the chlorine 3 p valence band to a new-type conduction band which is composed of alkylammonium bases and is below the ordinary Cd 5 s conduction band in energy.

Weak ferromagnetism of the layered perovskite (CnH2n+1NH3)2MnCl4 (n=1, 2 and 3)

Abstract Weak ferromagnetism in the layered perovskite (C n H2n+1NH3)2MnCl4((n = 1, 2 and 3) has been studied by means of neutron diffraction and SQUID magnetometry. The antiferromagnetic spin arrangement in all the compounds is consistent with the chemical unit cell of the tilt system of MnCl6 octahedra, alternately rotating about the b axis. The weak ferromagnetic moment due to spin canting in the direction of the a axis of the compound with n = 3 is 0.42 × 10−3 μB at 4.2 K; the spin canting can be ascribed to an antisymmetric exchange interaction through a coupling of the spin directions and the tilting directions of the MnCl6 octahedra. The critical index β of the antiferromagnetic moment and that of the weak ferromagnetic moment for this compound are 0.25 + 0.02 and 0.229 + 0.005, respectively; the results reflect the character of the two-dimensional magnetic system. For the compounds with n = 1 and 2 the weak ferromagnetic moments are found in the c-plane.

Optical Properties of Electron Trapped Center in Layered Ionic Crystals (CH3NH3)2CdCl4 and (C2H5NH3)2 CdCl4 Irradiated with X-Rays at 15 K

New optical absorption bands (IR bands) were found at around 10∼20 kcm -1 besides absorption band of Cl 2 - molecular center in two-dimensional crystals of (CH 3 NH 3 ) 2 CdCl 4 and (C 2 H 5 NH 3 ) 2 CdCl 4 irradiated with X-rays at 15 K. The absorption intensities increase with the X-ray dosage in proportion to that of the Cl 2 - center and decrease at temperatures higher than 25 K for (CH 3 NH 3 ) 2 CdCl 4 and 35 K for (C 2 H 5 NH 3 ) 2 CdCl 4 accompanying the decrease of Cl 2 - . The both bands are also bleached by the light irradiation on the IR bands at 15 K. The IR bands are assigned to an electron center where an electron is trapped by an alkylammonium head in the neighborhood of a Cl - vacancy.