Transient and steady-state conduction in ethyl cellulose (EC)–poly(methyl methacrylate) (PMMA) blends
✍ Scribed by P K Khare; R K Pandey; R R Chourasia; P L Jain
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 204 KB
- Volume
- 49
- Category
- Article
- ISSN
- 0959-8103
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✦ Synopsis
Transient discharging currents and steady-state conduction in solution-grown ethyl cellulose (EC)±poly(methyl methacrylate) (PMMA) blends measured as a function of temperature (30±80 °C) and ®eld strength (10±100 kV cm À1 ) are reported. Transient currents are found to follow the Curie±VonSchweidler law, characterized by different slopes in short-and long-time regions, having different decay constant values lying between 0.75±0.99, and 1.68±1.95. The corresponding activation energies are found to increase with time of measurement of discharge current. Isochronal characteristics (ie current versus temperature plots at constant times) constructed from the data seem to reveal a broad peak observed at 60 °C. The dependence of dark current at different temperatures (30±80 °C) in a metal (1)±EC±PMMA blend±metal (1)/(2) system on the applied voltage in the range 10± 100 kV cm À1 has also been studied; the current is found to be strongly temperature dependent. Dipole polarization and space charge resulting from trapping of injected charge carriers in energetically distributed traps and induced dipoles created because of the piling up of charge carriers at the phase boundary of the heterogeneous components of the blend are considered to account for the observed transient currents. The results of current±voltage measurement on blends are interpreted to show that the low-®eld steady-state conduction is ohmic in nature, and in high ®elds the charge carriers are generated by ®eld-assisted lowering of coulombic barriers at the traps and are conducted through the bulk of the material by a hopping process between the localized states by a Jonscher±Ansari Poole± Frenkel mechanism. The modi®ed P±F barrier is calculated to be 1.89 Â 10 À19 J (1.18 eV), 1.92 Â 10 À19 J (1.20 eV) and 1.95 Â 10 À19 J (1.22 eV) for P 1 , P 2 and P 3 blends, respectively.