抄録
The dielectric constants of urea-doped thiourea single crystals with different concentrations of impurity were measured. The impurity effects are shown to be significant near Tc and the intermediate commensurate phases of δ=1⁄8 and 1/9. For the urea-doped thiourea of relatively low concentrations, step-wise changes of the dielectric constant near Tc are observed. However, as the impurity concentration increases, step-wise changes near Tc disappear while sharp increase of the dielectric constant still remains. Remarkably, the intermediate commensurate phases are completely suppressed for the highly urea-doped sample. Pinning of discommensurations and suppression of the transitions to commensurate phases by impurities are discussed in conjunction with the experimental results.
