Metal temperature dependence

After Little s proposal, many researchers have pursued such an exciting system in vain. Even metallic behavior was rarely seen in doped organic polymers, gels, and actuators. As mentioned in Sect. 3.4.4, MCso with linearly polymerized Ceo" exhibited one-dimensional (M = Rb, Cs) or three-dimensional (M = K) metallic behavior [144]. Recently a doped poly aniline was reported to exhibit a metallic temperature dependence for a crystalline polymer chemical oxidation of monomers grew crystallite polyaniline [329] early doping studies on polypyrrole (PFg) and poly(3,4-ethylene-dioxythiophene)X (X = PFg, BF4, and CF3SO3) prepared by electrooxidation at low temperatures also showed a metallic temperature dependence below 10-20 K (Scheme 16) [330, 331]. 

Tens of conductive LB films have been developed so far, including metallic and superconductive LB films. These LB films are classified into the categories anion radical salt, charge-transfer complex, cation radical salt, conducting polymer, and transition metal complex in this section. The LB films, with metallic temperature dependences of conductivity, and the fullerene LB films, which exhibit a superconducting transition, are discussed separately. 

Figure 6.50. The temperature dependence of the diffusion rates Df along and across the chains for PANl-HCl with protonation levels y = 0.62 and 0.27. Note that D, shows metallic temperature dependence above ISO K for y = 0.62, and that Dx semiconducting with a temperature dependence similar to that of a [6,305,306,346] Reproduced from Synth. Met. 69 (1995) 241-2.

The spin dynamics of ESR was studied in polythiophene doped with C10, prepared by electrochemical polymerization at 300 K [296]. Heavily doped PT is known to show a metallic temperature dependence on ESR linewidth caused by the Elliott mechanism, characteristic of metals, as will be mentioned in section 7 [254,258,287,295,296]. In addition to this, a line broadening due to the spin dynamics is expected. Mizoguchi et al. reported the frequency dependence of the ESR linewidth in PT-CIO4 as shown in Figure 6.51 [296]. The filled circles do not behave simply following the prediction of (6.20) and (6.21) of Q-l-D spin motion, but there is a broadening mechanism other than... 

Recent studies have shown that this is not the case in polyacetylene improvements in synthesis and orientation have resulted in electrical conductivities as high as 10 S/cmA Furthermore, the absence of a metallic temperature dependence with resistivity decreasing as the temperature is lowered - implies that the measured conductivity is still limited by material imperfections. Consequendy, it is quite clear that the intrinsic electrical conductivity of polyacetylene and, by implication, of other conducting polymers, may be significantly greater than that of copper. 

In this work, highly conductive LB films of metal-(dmit)2 complexes and photochemical switching phenomena in the LB film are described. The LB films of tridecylmethylammonium-Au(dmit)2 showed a conductivity of 30 S/cm after electrochemical oxidation. Moreover, the film exhibited a metallic temperature dependence of the conductivity around room temperature. The conductivity of APT(8-12) was reversibly controlled by the photo-induced conformational change in azobenzene. This photo-responsive switching phenomenon can be repeated more than a hundred times. 

The resistivity of a polycrystalline sample of CaVOs showed a typical metallic temperature dependence, p(T) T, but it became higher above room temperature than is calculated on the basis of itinerant-electron scattering with a mean-free-path as short as one V—0—V distance, which makes CaVOs a bad metal. The resistivity also showed an unusually strong decrease with pressure as might be expected if pressure transfers charge carriers from a lower Hubbard band to the Fermi surface of a Fermi liquid. Pressure would increase not only Wb, but also coq, of Eq. (3), thereby broadening W. However, resistivity data on a polycrystalline sample may not be considered definitive, and they do not provide a measure of m. ... 

The metallic temperature dependence of S(T) observed at surprisingly low concentrations of PANI-CSA indicates that the microscopic conduction mechanism is not changed as PANI-CSA is diluted in PMMA. Although ai T) is strongly dependent on the mean free path and the number of connected pathways, S(T) is rather insensitive to the change in the number of pathways once the connected paths are formed above the percolation threshold. 

Depending on the crystalline morphology in which some charge transfer salts crystallize, e.g., TTF-TCNQ, they may be insulating or highly conductive. Today CT salts are also known with metallic temperature dependence of conductivity. 

The Langmuir-Blodgett (LB) films of alkylammonium-Au(dmit)2 and BEDO-TTF-alkylTCNQ show metallic temperature dependence at certain temperature ranges near RT. The ESR and thermopower measurements of the latter LB films suggest that the domain of the CT complex is metallic down to low temperatures and the conduction is activated by the domain boundaries. Superconducting thin films prepared by doping K into the Cgg LB film is reported with the onset 7). of 8.1 K. ... 

Nakamura, T., Kojima, K., Matsumoto, M., Tachibana, H., Tanaka, M., Manda, E., and Kawa-bata, Y., Metallic temperature dependence in the conductivity of Langmuir—Blodgett films of tridecylmethylammonium-Au(dmit)2, Chem. Lett., 367, 1989. 

In more recent work, Fukuhara et al. [202] have shown that application of about 13 kbar pressure to samples of P(3-Me-T)/PF6 gives rise to a metallic temperature dependence of resistivity (conductivity) at low temperatures below ca. 4 K, a dependence is observed. A study of thin films of P(ANi) at pressures up to 22 GPa at room temperature by Bao et al. [203] appeared to show enhanced interchain charge transport due to sample compression. Figs. 6-23(a-c) show some of the data obtained by these workers. 

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