Quantifying dielectric permittivities in the nonlinear regime.

In contrast to the static dielectric permittivity,ε, associated with linear response, its high-field counterpart,εE, is not a material specific quantity, but rather depends on the experimental method used to determine the nonlinear dielectric effect (NDE). Here, we defineεEin a manner consistent with how high field permittivities are typically derived from a capacitance measurement using high voltages. Based upon characterizing the materials nonlinear behavior via its third order susceptibility,χ3, the relations between a givenχ3and the observableεEis calculated for six different experimental or theoretical approaches to NDEs in the static limit. It is argued that the quantityχ3is superior overεEor the Piekara factor, (εE-ε)/E2, because it facilitates an unambiguous comparison among different experimental techniques and it provides a more robust connection between experiment and theory.