Yoshio Nogami

Recent structural investigations of metallic polymers

Abstract Recent structural studies of the undoped and iodine-doped polyacetylenes (prepared by the Tsukamoto and co-workers method), PF 6 − -doped polypyrrole and polyaniline emeraldine base and (hydrochloric acid and camphorsulfonic acid) salts are presented. Some key features of the polymer chain array and its evolution with the conditions of preparation are emphasized. Special attention has been devoted to characterization of the various sources of structural disorder in the relationship with high conductivity and related properties exhibited by these three families of polymers. Variation in the structural order in both crystalline and amorphous regions correlates directly with the electrical and optical properties of the metallic state.

On the metallic states in highly conducting iodine-doped polyacetylene

Abstract The temperature dependences of the conductivity, the magnetic susceptibility and the thermoelectric power of iodine-doped highly conducting ( ca. 10 5 S/cm) polyacetylene are presented. The conductivity shows non-activated behavior down to mK region. The density of states derived from the susceptibility and the thermoelectric power is consistent with one-electron band calculation. The electron localization due to the quasi one-dimensionality inherent to polymer is considered to beviolated by mesoscopic potential disorder, resulting in metallic strands, which are connected by tunneling.

Structure of highly conducting PF6−-doped polypyrrole

Abstract The structure of highly conducting PF 6 − -doped polypyrrole, the room-temperature conductivity of which is ≈ 1500 S/cm, is studied using X-ray ‘monochromatic’ Laue photographic methods. The ‘crystalline’ domain size along the polymer chain is estimated to be less than 20 A, while adjacent chains are rather well ordered with spacing of 3.4 A, suggesting that the system can be of two-dimensional nature. The influence of the structural properties on the high electrical conductivity is discussed.

Superlattice structural transition in the organic superconductor χ-(BEDT-TTF)2Cu[N(CN)2]Br

Abstract By the X-ray “monochromatic” Laue photographic method, we observe the formation below 200 K of superlattice reflections in χ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br which exhibits the highest superconducting critical temperature at ambient pressure (T c ∼ 11.6 K) among the organic superconductors. This displacive structural transition doubles the lattice parameter along c. We discuss the driving force of this instability and the consequences of this structural transition on the electronic and lattice properties of this salt.

Overview of organic superconductor κ-(BEDT-TTF)2[Cu(NCS)2] and its related materials

Abstract Crystal structures and physical properties of organic superconductors κ-(BEDT-TTF) 2 Cu(NCS) 2 , κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br and α-(BEDT-TTF) 2 [NH 4 Hg(SCN) 4 ] are discussed. The Cu(NCS) 2 salt shows an inverse isotope effect. The Cu[N(CN) 2 ]Br salt shows Tc of 11.7–11.8K. Conductivities, Hc 2 values and lattice parameters of these κ-type salts are compared.

Low temperature electrical conductivity of highly conducting iodine doped polyacetylene

Abstract The low temperature electrical conductivities of heavily iodine-doped polyacetylene with different degrees of disorder are reported. The sample with room temperature conductivity of 1.0 × 10 5 S/cm showed weak temperature dependence below 1 K down to 0.8 mK. With moderate increase of disorder, logarithmic temperature dependence was observed. The results are interpreted in terms of scattering of conduction carriers accompanying change of atomic configurations of equivalent energy in the polymer backbone, after similar process in amorphous metal alloys.

Low temperature transport properties of highly conducting polyacetylene

Abstract The temperature dependence of the electrical conductivity of the newly developed highly conducting polyacetylene, down to 60 mK, and its high field magnetoconductance up to 15 T are presented. The observed positive magnetoconductance for the most conducting sample exceeds by far the value based on the weak localization theory. The low temperature transport properties vary drastically with small change in the room-temperature conductivity, suggesting that the metallic conduction is realized in the scheme close to metal-nonmetal boundary.

Local structure of metal ions in arachidate Langmuir-Blodgett film

The fluorescence extended X-ray absorption fine structures near the Ba-L3 edge of a Ba-arachidate (CH3(CH2)18COO2Ba) Langmuir-Blodgett film are investigated by using polarized X-rays from a synchrotron radiation source. From the analysis of the observed spectra for different incident angles, the absorption-site geometries are obtained. The distance from the Ba ion to the nearest neighbor oxygen atoms, lying almost in the Ba plane, is found to be 0.278 nm. Taking account of the reported structural data, a local structure model around the Ba ion is proposed.

Electronic state density of highly conducting polyacetylene

Abstract The density of states of heavily I-doped highly conducting polyacetylene (HCPA) is evaluated through the magnetic susceptibility and the thermoelectric power measurements. According to the magnetic susceptibility, the density grows from ∼ 4% (in I3−-unit) doping level, in agreement with previous reports, but the attained value at ∼ 9% (saturating doping level) becomes larger than that for conventional polyacetylene.

Superconducting transition in κ-(BEDT-TTF)2Cu[N(CN)2]Br under magnetic field

Abstract Interlayer and intralayer coherence lengths of κ-(BEDT-TTF)2Cu[N(CN)2]Br are derived as ξ b (0)=6±2 A , ξ ac (0)=24±5 A , respectively, by magnetic measurement. The renormalized theory of the order parameter fluctuation near the superconducting transition region was employed for the analysis. The broad resistive transitions under magnetic field are discussed on the same footing.