Nonlinear dielectric constant of thiourea [SC(NH2)(2)] crystal

Abstract

The nonlinear dielectric constants of the thiourea crystal were measured up to the 5(th) nonlinear order (n=5) in the region of the commensurate phase transition. Odd harmonic responses (n=1, 3, 5) could be well explained by recent theories, but the even harmonic responses (n=2, 4) were found to be in disagreement with the available theories. Furthermore, the harmonic dielectric constants were observed even to change sign, depending on the thermodynamic hysteresis of the sample, that is, the sign of the spontaneous polarization at the time of the measurement. Increasing dispersions in the nonlinear dielectric responses were observed with increasing harmonic order n even when the linear response was in the region free of dispersion.