This paper presents the results of an investigation of microwave diele
ctric dispersion in the semiconductive ferroelectric Tl(InS2)(0.985) (
FeSe2)(0.015) in the frequency range 1 MHz to 110 GHz. Dielectric disp
ersion did not give any evidence for the existence of an incommensurat
e phase in these crystals. It is shown that dielectric dispersion is D
ebye type in the frequency range 10(6) to 10(11) Hz and is caused by t
wo relaxational soft modes. The magnitude of the activation energy for
the higher frequency relaxational mode is found to be U = 0.1 eV.