Two relaxators dielectric behaviour of ammonium hydrogen bis-chloroacetate near the ferroelectric phase transition

Dielectric response of the ammonium hydrogen bis-chloroacetate, NH4H(ClCH2COO)2 (AHCA), in the frequency range from 100 Hz to 10 GHz has been studied. In the temperature range close to the phase transition a two-relaxator dielectric behaviour was found. The high frequency (∼1 GHz) relaxator has properties of ferroelectric relaxational soft mode. The low frequency (∼10–100 MHz) relaxator displays properties common to the domain dielectric contribution known for some other ferroelectrics. The coexistence of the two dielectric relaxators in the vicinity of the phase transition is discussed using a conception of the free and pinned order clusters.