Domain glass dynamics of potassium thiocyanate (KSCN)

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 (LaAlO 3 , PbZrO 3 , SrTiO 3 , 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 τ D W with decreasing temperature can be well fitted by a Vogel-Fulcher law τ D W = τ 0 exp [ E a / k B ( T − T VF ) ] with τ 0 ≈ 10 − 7 s, E a ≈ 0.035 eV, and T V F ≈ 368 K, indicating domain glass behavior. The high frequency elastic moduli ( ∼ f 2 ) (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 T c = 415 K, which may be explained by order parameter fluctuations.