Impurity Effects on the Stability of Commensurate Phases of Thiourea

概要

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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 T_c 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 T_c are observed. However, as the impurity concentration increases, step-wise changes near T_c disappear while sharp increase of the dielectric constant still remains. Remarkably, the intermediate commensurate phases are completely sup-pressed for the highly urea-doped sample. Pinning of discommensurations and suppression of the transitions to commensurate phases by impurities are discussed in con-junction with the experimental results.
1993-01-15