In this work we provide a thorough examination of the nonlinear dielectricproperties of a succinonitrile-glutaronitrile mixture, representing one of therare example of a plastic crystal with fragile glassy dynamics. The detectedalteration of the complex dielectric permittivity under high fields can beexplained considering the heterogeneous nature of glassy dynamics and afield-induced variation of entropy. While the first mechanism was also found instructural glass formers, the latter effect seems to be typical for plasticcrystals. Morover, the third harmonic component of the dielectricsusceptibility is reported, revealing a spectral shape as predicted forcooperative molecular dynamics. In accord with the fragile nature of the glasstransition in this plastic crystal, we deduce a relatively strong temperaturedependence of the number of correlated molecules, in contrast to the muchweaker temperature dependence in plastic-crystalline cyclo-octanol, whose glasstransition is of strong nature.
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