Study of superionic phase transition of (NH4)4LiH3(SO4)4 by 1H MAS NMR

The temperature dependences of the line width, chemical shift, and spin–lattice relaxation time in the rotating frame, T1ρ, of the ammonium protons and hydrogen-bond protons in (NH4)4LiH3(SO4)4 are investigated by 1H MAS NMR. The change in the chemical shift for hydrogen-bond protons near the superionic phase transition TS (=405 K) indicates both H-bond breaking and new H-bond formation. Further, 1H T1ρ for the hydrogen-bond protons changes significantly near TS, and these protons play a more prominent role than the ammonium protons. Between TC (=232 K) and TS, molecular motions of the ammonium and hydrogen-bond protons occurred. The hydrogen-bond protons significantly influence the superionic phase transition of (NH4)4LiH3(SO4)4.