Phase Front Near the Critical End Point as the Boundary of the Polar Nanoregions in Relaxor Ferroelectrics

The static modulation structure of the phase front at the field-induced first-order transition point near the critical end point (CEP) was discussed on the basis of the Landau-type free-energy function. It was confirmed that the field $E$ dependence of the thickness of the phase front is proportional to $(E_{\text{CEP}}-E)^{-1/2}$, diverging at CEP ($E=E_{\text{CEP}}$). It is pointed out that, in relaxor ferroelectrics, the boundary between the polar nanoregion (PNR) and the paraelectric matrix may be considered as a phase front, and that the contribution to the dielectric response of the phase front cannot be ignored.