Dielectric Dispersion in Ferroelectrics [NH2(CH3)2]3Sb2Cl9 and [NH2(CH3)2]3Sb2Br9

Dielectric dispersion of [NH2(CH3)2]3Sb2Cl9 (DMACA) and [NH2(CH3)2]3Sb2Br9 (DMABA) single crystals is investigated over the frequency range 5 × 102 to 5 × 108 Hz. The dielectric behaviour of DMABA is determined by the properties of two relaxators: a low-frequency relaxator in the MHz region revealing critical slowing down and a high-frequency relaxator in the GHz region. Dielectric response of the DMACA crystal can be well fitted to a Debye law with only one relaxator which obeys the classical critical slowing down characteristic of a second-order phase transition.