 The theoretical slopes can be evaluated knowing the high frequency dielectric constant of the material (formula_25, where formula_26 is the vacuum permittivity), and confronting these with the slopes detected experimentally.As an alternative, one can evaluate the value for formula_27 equating the theoretical slopes to the experimental detected ones, provided that it is known if the conductivity is electrode-limited or bulk-limited.Such a value of the high frequency dielectric constant should then conform the relation formula_28, where formula_29 is the refractive index of the material.