Abstract
In polymers, the electronic activation energy depends on the fragmentation, crosslinking, dopants, moisture and in general on the structure-environment interaction. This has a special importance in plasma polymers because fragmentation and crosslinking are usually higher than in other polymers. In this work, DC electrical conductivity of polythiophene thin films prepared by plasma (pPTh) was studied using the Meyer-Neldel (MN) rule to calculate the characteristic MN energy and temperature as a function of moisture and metallic dopants. The experimental data for pPTh synthesized in different conditions indicated that EM = 32 meV and TM = 373 K, suggesting a thermally activated conduction mechanism; however, in polymer-metal matrices with metal concentration higher than the percolation threshold, the conduction mechanism is different causing that the MN rule was only partially fulfilled. The congruence of the experimental data with the multiexcitation entropy model is discussed.
Highlights
The electrical conductivity of semiconductors and many other materials following thermally activated processes obeys exponential expressions similar to the Arrhenius equation, see Equation (1) where k is the Boltzmann constant, Ea is the activation energy and σo is a pre-exponential factor
In a model with metallic islands surrounded by insulating barriers, a material with better structural order could enhance their electrical conductivity as the model suggest by Pinto [8]
Conductivity shows no evident correlation with ordered structures or synthesis time to apply a crystalline islands model
Summary
The electrical conductivity of semiconductors and many other materials following thermally activated processes obeys exponential expressions similar to the Arrhenius equation, see Equation (1) where k is the Boltzmann constant, Ea is the activation energy and σo is a pre-exponential factor. In this expression, σ tends to σo when T increases at high values. As σo correlates with Ea, in 1937 Meyer and Neldel proposed an empirical expression called the Meyer-Neldel (MN) rule [1] [2], see Equation (2), where σoo is another MN pre-exponential factor and EM = kTM is a characteristic energy (the MN energy) of the material at TM (the MN characteristic temperature). The MN rule is found in literature as the compensation law and has been observed in crystalline, amorphous, organic and inorganic materials [3] [4], but a physical interpretation of EM and σoo is still not clear enough
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