1H and 87Rb nuclear magnetic resonance study of the order–disorder phase transition of RbHSeO 4 single crystals

Abstract

The ferroelectric phase transition at T C2 (=370 K) in RbHSeO 4 has been studied by 1H and 87Rb solid-state NMR. Although not large, the spin–lattice relaxation time, T 1, and the spin–spin relaxation time, T 2, of rubidium and of the α- and β-type protons show distinct change near the phase transition. The intensity of the signal due to the α-type protons decreases with increasing temperature, and the intensity of α-type protons is quite weak above 330 K: at a temperature which is about 40 K lower than the phase transition temperature, the ordering of the α-type protons occurs. The α-type protons in the ferroelectric phase lead to a noticeable change in the proton magnetic resonance spectra. Our study of the 1H spectra shows that the ferroelectric phase transition in RbHSeO 4 is of order–disorder type and is due to the ordering of protons in hydrogen bonds.