Hi there, 

When draw the log i vs. E, get a Tafel plot to estimate the current and voltage values at the maximum condition of the scan rate.

Regards, 

The minimum current is observed at equilibrium potential. For low overpotential values in both direction, the potential dependence of logi is not linear. In this region, charge transfer is the limiting mechanism. In fact, the exchange current can be calculated in this reqion. This region is also called polarization resistance region. At sufficiently great or small overpotential values, begun at around 200mv far from equilibrium potential, the reaction rate is controlled by diffusion of the electroactive material and the potential dependence of logi becomes linear.

Thank you for the answers but I must ask for further clarification. 

To Qhatan Adnan Yousif, what do you mean when you say maximum scan rate? and I also pose the same question that I have asked below. 

Hamid Reza Moazami, it seems you are referring to electrochemical systems where some sort of reaction is taking place at the electrodes. I must stress that, the data obtained are from a solid ceramic pellet know for its multiferroic properties; not any electrochemical system in the traditional sense. What kind of reactions may be taking place in this system? Can a solid be expected to show such behavior? 

I think that Qhatan is trying to say that you should test some scan rates in order to determine when an increase on it does not cause any change in the plot obtained, that is, that your system is under mass transfer control.

On the other hand, Hamid referred to any electrochemical system. You have a ceramic pellet with iron in its composition, don't you?. Then, that iron may pass from one oxidation state to the other inside your pellet.

Tafel plots are usually obtained to study the corrosion properties of solid materials, then, the answer to your question is yes, a solid can be expected to show such behaviour.