Dc Conductivity Experiment

DC electrical conductivity is one of the useful techniques to study the conductivity mechanism. The DC conductivity set-up is shown in fig.2.17.The DC conductivity was measured as a function of temperature by two Probe method using Keithley electrometer in the temperature range 303K to 473K. [38]. A constant voltage was applied to the pellets of samples and the current through the sample was measured using digital nanometer. The temperature of the sample was measured by a temperature control unit provided with Chromm Alumel thermocouple. The conductivity was determined using the relation σ=t/RA where ‘t’ is the thickness of the sample,

’ R’ is the resistance and

‘A’ is area of cross section of the samples.[39-40].

2.6.1

This expression is often subtracted from the imaginary component of the permittivity to account for dielectric relaxation processes not involved in long-range charge transport. The resultant expression for the complex permittivity is ε^*=ε^'-i(ε^"-σ_DC/(ωε_0 ))

This equation makes the assumption that the transport mechanism, leading to long- range DC conductivity, has no influence on the complex permittivity other than the contribution from equation 3. This in turn implies that the conductance process can be defined by one relaxation time, τ_(σ )=(ε_0