1H and 87Rb nuclear magnetic resonance study of the order-disorder phase transition of RbHSeO4 single crystals

The ferroelectric phase transition at TC2 (=370 K) in RbHSeO4 has been studied by 1H and 87Rb solid-state NMR. Although not large, the spin-lattice relaxation time, T1, and the spin-spin relaxation time, T2, 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 RbHSeO4 is of order-disorder type and is due to the ordering of protons in hydrogen bonds.