Domain glass dynamics of potassium thiocyanate (KSCN)

Abstract

We study the dynamic elastic behavior of potassium thiocyanate (KSCN) in the temperature region of the order-disorder improper ferroelastic phase transition using dynamic mechanical analysis (0.05-40 Hz) and resonance ultrasound spectroscopy (100-600 kHz). The low frequency data show—in addition to the intrinsic phase transition anomalies—softening in a- and b-directions below T c , which results from movements of ferroelastic domain walls under dynamic stress. In contrast to many other ferroelastic materials (LaAlO₃ , PbZrO₃ , SrTiO₃ , etc.), the domain wall motion in KSCN freezes already at a temperature below T c -20 K. The corresponding increase of the domain wall relaxation time τDW with decreasing temperature can be well fitted by a Vogel-Fulcher law τDW = τ₀ exp[Ea / kB ( T−TVF )] with τ₀ ≈ 10⁻⁷s, Eₐ ≈ 0.035 eV, and TVF ≈ 368 K, indicating domain glass behavior. The high frequency elastic moduli ( ∼ f² ) (100-600 kHz) do not show any precursor softening with decreasing temperature due to the large order parameter relaxation time τ η. In contrast to the high frequency elastic moduli, the corresponding losses Q⁻¹ exhibit peaks at Tc = 415 K, which may be explained by order parameter fluctuations.