Phase transition by 7Li NMR in a LiNH4SO4 single crystal

The temperature dependence of the 7Li nuclear magnetic resonance in a LiNH4SO4 single crystal grown by the slow evaporation method has been investigated by employing a FT NMR spectrometer. The rotation patterns of the 7Li NMR spectra were obtained in three mutually perpendicular planes under an applied magnetic field of 4.7 T. The 7Li NMR spectra demonstrates the occurrence of the first-order phase transition at TC (=285 K). Two different groups of Li resonances were recorded below TC. The two groups represent the transition of 7Li NMR lines due to Li(I) and Li(II), respectively; the two signals are associated with two physically inequivalent positions of lithium atoms in the unit cell. The principal axes of the EFG tensor below TC are not the same as those above TC. The temperature dependence of e2qQ/h and η in the temperature range of 170–400 K is explained with a single torsional frequency of the Li–O ion by means of the simple Bayer theory.