Dielectric Relaxation in Ferroelectric MASD, CH₃NH₃Al(SO₄)₂·12H₂O

Abstract

The complex dielectric constant of methylammonium aluminum sulfate dodecahydrate, CH 3 NH 3 Al(SO 4 ) 2 ·12H 2 O, was measured at various frequencies in a frequency range between 1×10 6 and 1×10 9 Hz in its para- and ferroelectric temperature regions. The experimental result was analyzed for the paraelectric phase. The crystal exhibits critical slowing-down process of polarization. The observed temperature and frequency dependences of the complex dielectric constant can be described to good approximation in terms of a single relaxation time τ( T ) of Debye type. Above the Curie point ( T c ), the static dielectric constant follows the Curie-Weiss law (( ε 0 - ε ∞ )∼( T - T 0 ) -1 ), while τ( T ) is described well by the relation τ( T )=α·( T - T 0 ) -1 ·exp ( Δ U / k B T ) with the potential barrier height Δ U =(2.18±0.06) kcal·mol -1 and α=(0.92±0.14) ( h / k B ).