Non-linear dielectric properties of KTa1-xNbxO3

The field dependence of the dielectric constant in two crystals of KTa_1-xNb_xO₃ with x=1.2% and 15.7%, respectively was measured. For both concentrations ∈(E) was fitted with an expansion in powers of the applied DC field E to find the first nonlinear coefficient, ∈⁽²⁾. ∈⁽²⁾ exhibits two distinct temperature dependences: first, at high temperature, a strong divergence as (T-T_c)^-9, and then a crossover to a much weaker dependence. This crossover is interpreted as being from a dynamic to a static regime. Theoretical modeling in progress is presented