  The polaron to bipolaron transition in disordered media under the influence
of a broadband ac electric field is suggested: ac conductivity vs. frequency
measurements in disordered media with inhomogeneous disorder induce
spatio-temporal fluctuations of the density of polarons yielding polaron to
bipolaron transformation. The external field results in the transition,
alternatively to an increasing doping level. The assertion is confirmed by
performing successive complex impedance measurements in disordered media. A
systematic increase of the real part of the ac conductivity in the frequency
domain, followed by mutual reduction of the magnetic inductivity of conducting
polypyrrole, are explained.
