Electron Hopping Conduction Research Articles

Decaying and steady currents in an epoxy polymer at high electric fields

Measurements are reported of the effect of field and temperature on decaying and steady currents in an epoxy polymer. Fields up to 140 MV m−1 were used and the steady current was found to increase as exp (α F½). The decaying currents followed the t−n law and increased much less rapidly with increasing field and temperature than did the steady currents.Absorption of water by the polymer caused a marked increase in steady-state conduction but the current characteristics were similar to those of dried specimens.It is suggested that the decaying currents are due to electronic hopping conduction, whereas the steady currents are ionic.

Induced electron emission spectroscopy of reduced lead silicate glass (X-ray photoemission)

A measurement of the induced electron emission spectrum (IEE) of lead in reduced lead silicate glass indicates that the lead in this system exists in three different charge states Pb 0, Pb 1+, and Pb 2+. An electronic hopping conduction mechanism employing these three states is proposed.

A dislocation model for two-level electron-hopping conductivity in V 2O 5: Implications for catalysis

The electrical conductivity of single-crystal V 2O 5 and V 2O 5 doped with copper (α phase) has been measured along the c axis from 77°K to 298°K. Ln σ vs. 1 T can be approximated by two straight lines with an average activation energy above 170°K of 0.20 eV and below 170°K of 0.077 eV. Comparison with EPR data and with the V 2O 5-β phase leads to an interpretation for the high-temperature conductivity as arising from thermal excitation of electrons from vanadium-pair traps with an activation energy of 0.15 eV and electron hopping from one vanadium site to another with an activation energy of 0.05 eV. Together with the Seebeck coefficient, the low-temperature data also require direct electron hopping between traps with an activation energy of 0.077 eV. A dislocation model is presented to account for the vanadium pair traps, the electrical conductivity and EPR data. The model require the formation of interstitial oxygen which it is suggested may be involved in the catalytic properties of V 2O 5.

Studies On The Electrical Properties Of Cu Substituted Li-Ferrites

Polycrystalline Li-Cu mixed ferrites were prepared by double sintering ceramic technique. Cu substituted Li ferrites having the general formula Li0.5-x/2CuxFe2.5-x/2O4 where, x = 0.0 to 1.0 and the samples were sintered at 1100°C for 3 hours in the normal atmosphere. The prepared samples were confirmed in the spinel structure by the X-ray diffraction method. The lattice parameter and porosity were calculated for different compositions. The electrical resistivity and dielectric constant have been investigated as a function of composition and temperature. It was observed that the resistivity decreased with increasing temperature and exhibited semiconducting nature of the sample. The compositional variation of resistivity and dielectric constant showed inversed trend with each other at room temperature for Cu content, x > 0.3. This was found to support the electron hopping conduction mechanism. The dielectric constant increased slowly with temperature in the beginning and after that dielectric constant increased rapidly for different samples. As the temperature increased, thermal energy provided to the sample played an important role to decrease the relaxation time and hence there was an increase in dielectric constant. Dielectric constant has been observed as a function of frequency and it decreased with increasing frequency. Key words: Electrical resistivity; Porosity; Dielectric constant; Electron hopping DOI: http://dx.doi.org/10.3329/jbas.v35i2.9428 JBAS 2011; 35(2): 221-228