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

Abstract

The complex dielectric constant of methylammonium aluminum sulfate dodecahydrate, CH₃NH₃Al(SO₄)₂·12H₂O, was measured at various frequencies in a frequency range between 1×10⁶ and 1×10⁹Hz 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 ((ε₀−ε_∞)∼(T−T₀)⁻¹), while τ(T) is described well by the relation τ(T)=α·(T−T₀)⁻¹·exp(ΔU⁄k_BT) with the potential barrier height ΔU=(2.18±0.06) kcal·mol⁻¹ and α=(0.92±0.14) (h⁄k_B).