Nonlinear dielectric characteristics and domain wall freezing in KH₂PO₄

Abstract

Nonlinear dielectric constants, ε _n ’ (real part) and ε _n ” (imaginary part), of higher order harmonic responses (up to n=9) were measured in KH₂PO₄(KDP) crystal near the domain wall freezing temperature T_f ≃ 96K by use of a precision dual phase lock-in amplifier system. The observed dependence of ε _n ’ and ε _n ” on a.c. field amplitude can be understood in terms of the nonlinear polarization dynamics as due to the domain wall motions characterized by a critical field E_c, a power law exponent a, and phase retardation φ.