It is shown that the reentrant Sm-${\mathit{C}}^{\mathrm{*}}$ phase in an external magnetic as well as in an external electric field in typical ferroelectric liquid-crystalline compounds, such as p-(n-decyloxybenzylidene)-p’-amino-(2-methylbutyl) cinnamate (DOBAMBC), has the same physical origin as the anomalous temperature dependence of the pitch p. The observed temperature dependence of the critical electric field ${\mathit{E}}_{\mathit{c}}$ is described well within the extended Landau model using the same values of the model parameters as in the magnetic-field case [Phys. Rev. E 48, 455 (1993)]. In DOBAMBC a simple relationship between ${\mathit{E}}_{\mathit{c}}$, the tilt Θ, the polarization P, and the pitch p in a zero field, ${\mathit{E}}_{\mathit{c}}$∝${\mathrm{\Theta }}^2$/(${\mathit{Pp}}^2$) is found to be valid at all temperatures except for ${\mathit{T}}_{\mathit{c}}$-T≲0.1 K. At temperatures 0.2 mK<${\mathit{T}}_{\mathit{c}}$-T<2.5 mK, where the Sm-${\mathit{C}}^{\mathrm{*}}$⇆Sm-C transition is first order, the stability limits of both phases are determined: the associated hysteresis is found to be small.

• Received 23 June 1994

DOI:https://doi.org/10.1103/PhysRevE.51.1569