Microwave study of the soft ferroelectric mode in TlGaSe2

Abstract
The paper presents the results of the microwave investigations of the dielectric dispersion in semiconducting ferroelectric TlGaSe2 crystals over the frequency region from 0.6 to 78 GHz. The dielectric dispersion is caused by the strongly overdamped soft resonant ferroelectric mode. In the paraelectric phase, its frequency varies according to vr2 = A (T - Tc) with A = (500 ± 50) GHz2 K-1. At the Curie point Tc the frequency vr = 60 GHz, and the damping constant γ = 250 GHz. The large anharmonicity of the soft ferroelectric mode causes the dispersion of the dielectric permittivity of TlGaSe2 crystals over the whole microwave frequency region.