ND4 DEUTERON NMR-STUDY OF (ND4)(4)LID3(SO4)(4)

(ND4)(4)LiD3(SO4)(4) has been investigated by pulsed Fourier transform ammonium deuteron NMR in the temperature region between 74 and 415 K. At 415 E in the superionic phase the observed lineshape gives a hint for translational diffusion of ND4 groups. A non-zero ND4 deuteron lin e splitting is observed which seems to indicate that the ammonium grou ps are flipping between two non-equivalent orientations while rotating around more than one axis. Comparison of the experimental data for th e splitting with Landau theory shows that the phase transition in (ND4 )(4)LiD3(SO4)(4) is of second order.