Investigation of phase transition mechanisms of CsH3(SeO3)2 single crystals by observation of nuclear magnetic resonance

The relaxation times of the 1H and 133Cs nuclei in CsH3(SeO3)2 crystals were investigated using FT NMR. The 133Cs spectrum does change from seven resonance lines to one resonance line near Tm (=350 K). The presence of only one 133Cs signal is due to the liquid state resulting from the melting of the crystal. The variation in the separation of the 133Cs resonance lines with temperature indicates that the EFG at the Cs sites produced by the (SeO3)2− groups varies with temperature, which in turn means that the atoms neighboring 133Cs are displaced. And, the T1 for 133Cs is very long and undergoes significant changes near Tm. The change in the temperature dependence of T1 at Tm for the 133Cs nuclei coincides with the melting temperature. These results are compared with those obtained for MH3(SeO3)2 (M=Na, K, and Cs) crystals.