Temperature-Dependent Conductivity

To find models and physical descriptions of the charge transport in conjugated polymers, it is useful to consider the temperature dependence of parameters, such as conductivity and thermopower, of those polymers. Some typical features of metals and semiconductors have already been pointed out. 

In a metal the conductivity remains finite as the temperature approaches 0. This is due to the fact that there are delocalized electronic states at the Fermi 

There are only very few cases in which a decrease in conductivity has been observed over the whole temperature range. Park et al. reported in 1998 a perchlorate doped polyacetylene, which showed a decrease of conductivity with increasing temperature over the whole temperature range for the first time. Hence this sample shows two features of mefallic behavior a nonzero conductivity at T = 0 and a decrease of conducfivify wifh increasing temperature. 

BORONIC ACID SUBSTITUTED SELF-DOPED POLYANILINE 

The conductivity of self-doped PABA without heat treatment was observed to be around 0.96 S/cm. This conductivity value is consistent with the 21 % doping suggested by NMR based on the conductivities of other forms of self-doped polyanilines [110, 113]. However, the conductivity was lower than HCl doped polyaniline, probably due to distortion of the polymer backbone by the presence of the boronic acid substituent [116-118]. After heat treatment at 100 and 500°C, a decrease in conductivity from 0.96 S/cm (without heat treatment) to 0.094 and 0.009 S/cm, respectively was observed. However, in the case of polyaniline, the conductivities of the heat treated polyaniline declined significantly compared with that of the self-doped PABA. The relative decrease in conductivity of heat treated PABA was less than that of HCl-doped polyaniline, probably due to the formation of a thermally stable boronic acid anhydride crosslink. In the case of polyaniline, the dramatic decrease in conductivity was a result of the decomposition of the backbone above 420 °C, as seen in the thermograms. In contrast, the process of crosslinking in the PABA polymer above 100 °C may make 

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Arrhenius plots of temperature-dependent conductivity for [EMIM][BF4] (O), [EMIM][(CF3S02)2N] ( ), and [PMMIM][(CF3S02)2N]... 

For example, the final heat treatment temperatures In the manufacture will produce different electrochemical properties, even with the same surface treatments (2-4) since the structure and electrical property of glassy carbon depends on the temperature, as Indicated by the single crystal TEM patterns and by measurement of temperature dependent conductivity (5-6). On the other hand. It Is also well established that the electrochemical properties of carbon-based electrodes are markedly affected by surface treatments. 

From comparable systems with a particle-size distribution width of 7%, experimental and computational results for temperature-dependent conductivity measurements were reported on by Remade et al. [57]. At low temperatures, the I(U) characteristics have a sigmoid shape and are non-linear (Figure 25). 

Many polymer-salt complexes based on PEO can be obtained as crystalline or amorphous phases depending on the composition, temperature and method of preparation. The crystalline polymer-salt complexes invariably exhibit inferior conductivity to the amorphous complexes above their glass transition temperatures, where segments of the polymer are in rapid motion. This indicates the importance of polymer segmental motion in ion transport. The high conductivity of the amorphous phase is vividly seen in the temperature-dependent conductivity of poly(ethylene oxide) complexes of metal salts. Fig. 5.3, for which a metastable amorphous phase can be prepared and compared with the corresponding crystalline material (Stainer, Hardy, Whitmore and Shriver, 1984). For systems where the amorphous and crystalline polymer-salt coexist, NMR also indicates that ion transport occurs predominantly in the amorphous phase. An early observation by Armand and later confirmed by others was that the... 

Fig. 5.3 Comparison of the temperature-dependent conductivities for amorphous PE0 NH4SCN (circles) and crystalline PEO NH4SCN (squares).

LB films prepared from tridecylmethyl-ammonium Au-(dmit)2 and H2dmit = 4,5-dimercapto-l,3-dithiol-2-thione, transferred to hydrophobized glass substrates, and oxidized (by Br2 or electrochemicaily) Absorption spectra and temperature-dependent conductivity measurements... 

Procarione and Kaufmann (49) studied the electrical properties of phospholipid bilayers between metal contacts. They observed, for example, irregularities in current and capacitance vs. temperature data which may be the result of phase transitions in the lipid bilayer. They also observed that both temperature-independent (tunneling) and temperature-dependent conduction processes with an activation energy of 0.65 eV were important. 

Fig. 1.2. Arrhenius plot of the temperature-dependent conductivity of an extrinsic semiconductor.

Fig. 10 Temperature dependent conductivity a for Me-PVP1940I, cp=5 glT1, Q=80%. a Raw data (y) with salt reference measurements (solid line 0.03 M Nal). b Polyelectrolyte conductivity Act after subtraction of the reference measurement. (A, O) repeated measurements...

Fig. 13 Temperature dependent conductivity measurements for Et-PVP1940I at Q=40% ( ) with a salt reference measurement line)...

For highly quaternized polyelectrolytes, temperature dependent conductivity measurements exhibit a sudden drop of conductivity while crossing... 

Fig. 2.2. Temperature-dependent conductivity of different ZnO samples, measured by Fritsch in 1935 [9]. All samples were not intentionally doped. (1) and (2) are as grown and annealed polycrystalline ZnO samples, respectively. The lowest conductivities and the largest activation energies exhibit the annealed single crystals (3)...

Figure 4. The complex Cs[Pd(dmit)2]2- (a) temperature-dependent conductivity. [Adapted from (82).] (b) projection of the crystal structure onto the ac plane. [Drawn from the data available in (84).] (c) Projection of the crystal structure along the c axis. [Drawn from the data available in (84).]...

Fig. 61 a Conductive supramolecular poly(anilines) with pendant side-chains, b Temperature dependent conductivities of the complexes. Reprinted with permission from [215]... 

Association Constants, Gibbs Energies, Enthalpies, and Entropies of Ion-Pair Formation of Alkaii Metai and Tetraaikylammonium Iodides in 1-Propanol from Temperature-Dependent Conductivity Measurements... 

The value of To and Tj are obtained from a computer fit of the temperature dependent conductivity data and expressed as geometrical factors containing the height and thickness of the barriers [83, 165, 175]. 

Temperature dependent conductivity studies reveal a metallic character of the salt and the remarkably high conductivity of 500000 S/cm at 3.5 K. It should be noted that the TCNQ copper salt is a semiconductor with a room-temperature conductivity of 2x 10 S/cm. The crystal structure of the salt TCNQI 2Cu reveals segregated columns formed from the quinone and the copper ion whereby the copper chains are surrounded by 4 quinone stacks [344]. 

The Tg may also increase as a result of increased interactions between ion pairs and the formation of ion clusters. The increase in Tg is nearly linear with the ratio Li /EO, even up to a ratio of 0.5 for LiCF3S03 solubilized in PM MS-8 or in the identical poly(methacrylate) comb polymer (Figure 3). The rise in Tg is much more rapid for the poly(methacrylate) comb polymer than for the polysiloxane. The free-volume mechanism of ion conduction is confirmed in our system by the linearity of temperature-dependent conductivity plots when the Vogel-Tammann-Fulcher (VTF) expression a = exp [-K T - rj] (in which is the ideal Tg and and K are constants) (i, 2, 9) is applied. 

Fig. 34. Temperature dependent conductivities (a) of MEEP-NaMMT parallel to the composite layers, (- ) VTF fit (-) (MEEP). NaMMT perpendicular to the composite layers, (i ) VTF fit (-) Pristine Na.MMT ( ) measured perpendicular to the layers...

Figure 8. Temperature-dependent conductivity of thin film simple oxides and a-Fe203-Sn02 composites in air, RH 30%...

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