  The distribution function of relaxation times in disordered dielectrics has
been calculated in the random field theory framework. For this purpose, we
first consider the dynamics of single two-orientable impurity electric dipole
in a random electric field $E$ created by the rest of impurities in disordered
ferroelectric. This dynamics is conveniently described by Langevin equation.
Relaxation time $\tau $ is then a reciprocal probability (calculated on the
base of Fokker-Planck equation) of the dipole transition through barrier in a
double-well potential (corresponding to two possible dipole orientations),
distorted by a random fields. The obtained dependence $\tau (E)$ made it
possible to obtain the expression for relaxation times distribution function
$F(\tau)$(via random fields distribution function $f(E)$. Latter function has
been calculated self-consistently in the random field theory framework.
Nonlinear random field contribution and effects of spatial correlations between
impurities have also been taken into account. It was shown that nonlinear
contribution of random field gives asymmetric shape of $F(\tau)$, while in
linear case it is symmetric. Comparison of calculated $F(\tau)$ curves with
those extracted from empirical Cole-Cole (CC), Davidson-Cole (DC),
Kohlrausch-William-Watts (KWW) and Havriliak-Negami (HN) functions had shown,
that they correspond to mixed ferro-glass phase with coexistence of short and
long-range order. Different forms of $F(\tau)$ are determined by linear (CC) or
nonlinear (DC, KWW, HN) contributions of random field.
