For materials such as Si 3 N 4, Al 2 O 3, and SiO 2, at high temperature and high field regimes, the current J is likely due to Poole–Frenkel emission. The detection of Poole–Frenkel emission as the limiting conduction process in a dielectric is usually made studying the slope in the so-called Poole–Frenkel plot, where the logarithm of the current density divided by the field ( l n ( J / E ) ) versus the square root of the field ( E ) is depicted. The idea of such a plot originates from the expression of the Poole–Frenkel current density, which contains this proportionality ( l n ( J / E ) vs E ), and would thus result in a straight line in this plot. For a fixed value of the voltage barrier in absence of any applied electric field, the slope is influenced by just one parameter: the dielectric permittivity. Despite the same functional dependence of the current density upon the electric field intensity, one could differentiate between Poole–Frenkel conduction upon Schottky conduction as they would result in straight lines with different slopes in a Poole–Frenkel plot. The theoretical slopes can be evaluated knowing the high frequency dielectric constant of the material ( κ κ = ϵ ϵ / ϵ ϵ 0 , where ϵ ϵ 0 is the vacuum permittivity), and comparing these with the slopes detected experimentally. As an alternative, one can evaluate the value for κ κ 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 κ κ = n 2 , where n is the refractive index of the material.