Superionic phase transitions and nuclear spin phonon relaxation by Raman processes inMe3H(SeO4)2 (Me = Na, K, and Rb)single crystals by 1H and Me NMR

Abstract

Me3H(SeO4)2 (Me = Na, K, and Rb) single crystals were grown by the slow evaporation method, and the relaxation times ofthe 1H and Me nuclei in these crystals were investigated using FT NMR spectrometry. The1H T1 NMRresults for K3H(SeO4)2 and Rb3H(SeO4)2 single crystals were very different from those forNa3H(SeO4)2 crystals. Short1H relaxation timeswere found for K3H(SeO4)2 andRb3H(SeO4)2 at high temperatures,but not for Na3H(SeO4)2, which are attributed to the destruction and reconstruction of hydrogen bonds; thusK3H(SeO4)2 andRb3H(SeO4)2 have superionicphases, whereas Na3H(SeO4)2 does not. The temperature dependence of the relaxation rate for the23Na nucleusin Na3H(SeO4)2 crystals was in accord with a Raman process for nuclear spin–lattice relaxation. In contrast, the spin–lattice relaxation rates for the39K and87Rb nucleiin K3H(SeO4)2 and Rb3H(SeO4)2 single crystals exhibited a very strong temperature dependence, . The motions giving rise to this strong temperature dependence may be related to thehigh electrical conductivities of these crystals at high temperatures.