Ferroelastic domain wall motion and collective domain switching in RbSCN

Low-frequency (0.05–40 Hz) dynamic elastic measurements and resonant ultrasound spectroscopy measurements (100–600 kHz) of RbSCN were performed in the temperature region of the order-disorder improper ferroelastic phase transition at T c ≈ 435 K. Quite similar to KSCN, the low-frequency data show, in addition to the intrinsic phase transition anomalies, superelastic softening in the a and b directions, resulting from movements of ferroelastic domain walls under dynamic stress. However, in contrast to KSCN, a sudden discontinuous increase of Young's modulus appears in RbSCN at T * < T c , which is accompanied by a frequency-dependent damping peak. This behavior is reminiscent of a first-order phase transition. Heating RbSCN slightly above T * , followed by subsequent cooling, removes all signs of domain wall dynamics. The results demonstrate that the anomalies in RbSCN around T * result from collective domain switching events that are induced when the temperature-dependent critical pinning stress σ c ( T ) falls below the applied external stress σ , implying that T * ( σ = σ c ) . This interpretation is supported by calculations of the temperature dependences of twin boundary widths w and energies F w , as well as the Peierls potential V 0 using a compressible pseudospin model, which leads to a critical pinning stress σ c ( T ) that is in excellent agreement with experimental values of T * ( σ c ) .