Study on the dynamics of NaHXO4 and Na3H(XO4)2 (X=S,Se) crystals by observation of the H1 and N23a spin-lattice relaxations

Abstract

The relaxation times of the H1 and N23a nuclei in NaHXO4 and Na3H(XO4)2 (X=S,Se) single crystals were investigated. The H1 spin-lattice relaxation times T1 obtained for the four crystals were found to be very different from those determined for MeHXO4 and Me3H(XO4)2 crystals containing metals other than Na. Short H1 relaxation times were found at high temperatures for MeHXO4 and Me3H(XO4)2 when Me=K, Rb, or Cs and X=S or Se, but not for NaHXO4 and Na3H(XO4)2. The reason for this behavior is that the NaHXO4 and Na3H(XO4)2 crystals possess very short hydrogen bonds, these bonds being longer in NaHSO4 than in the other three sodium-based crystals. Furthermore, the temperature dependences of the relaxation rates observed for the N23a nuclei in NaHSeO4, Na3H(SO4)2, and Na3H(SeO4)2 were found to be in accordance with a Raman process (i.e.,T1−1∝T2), whereas the spin-lattice relaxation rate for the N23a nucleus in NaHSO4 exhibited a very strong temperature dependence (T1−1∝T7). This strong temperature dependence and the longer hydrogen bonds in the NaHSO4 crystals may both be related to the superionic character of NaHSO4 at high temperatures.