Nonlinear dielectric characteristics and domain wall freezing in KH2PO4

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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 Tf ≃ 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 Ec, a power law exponent a, and phase retardation φ.