Vogel-Fulcher relationship for the dielectric permittivity of relaxor ferroelectrics

The low frequency dielectric response of relaxor 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 temperautre 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.