Ferroelastic to paraelastic phase transition of K3H(SeO4)(2) and Rb3H(SeO4)(2) single crystals studied by nuclear magnetic resonance and external stress

Abstract

The temperature dependences of the nuclear magnetic resonance (NMR) and the stress-strain hysteresis curves have been measured for K3H(SeO4)(2) and Rb3H(SeO4)(2) crystals grown using the slow evaporation method. By analysis of the K-39 and Rb-87 NMR results, it has been confirmed that the phase below T-C is ferroelastic with twin domains and that the phase above T-C is paraelastic with a single domain. The ferroelastic domain switching that occurs in the two single crystals due to external stress was also studied. The critical stress values for converting the twin-domain state to the single-domain state were obtained. When external stresses of 0.6 and 0.4 MPa were applied to the K3H(SeO4)(2) and Rb3H(SeO4)(2) crystals, respectively, transitions from twin-domain to single-domain states were observed. The ferroelastic domain switching resulting from an external stress may be associated with the atomic rearrangements of the SeO4 tetrahedra in K3H(SeO4)(2) and Rb3H(SeO4)(2) crystals; the ferroelastic domain switching is explained by the restriction of the rotation of the SeO4 tetrahedra as a result of the breaking of all hydrogen bonds by the external stress. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.