Vogel-Fulcher Relationship for the Dielectric Permittivity of Relaxor Ferroelectrics

The low frequency dielectric response of relaxer ferroelectrics is analyzed. Following the conventional approach this response is considered as a sum of those of relaxators having an exponentially wide and smooth spectrum of the relaxation times. It is shown that the Vogel-Fulcher relationship for the positions of the temperature maximum for the real and imaginary parts of the dielectric permittivity can be obtained as a direct consequence of gradual broadening of the spectrum with decreasing temperature. It is shown that such a Vogel-Fulcher-type relationship does not necessarily imply ''freezing'' in the system.