Fig. 3: Reorientation dynamics of ammonia molecule.

a–c Spectral fitting of the sliced S(Q,ω) over the Q range of [1.55, 1.65] Å⁻¹ at (a) 160, (b) 260, and (c) 300 K, respectively. One constant background (BKG) plus a delta function convoluted with the resolution function could make a good fitting for the spectrum at 160 K, while one more Lorentzian profile is needed at 260 and 300 K. d Temperature dependence of the full width at half maximum, Γ, of the Lorentzian components for the intermediate-T β-phase and the high-T α-phase, which are fitted to the Arrhenius equation, \(\varGamma \propto {{\exp }}\left(-\frac{{E}_{a}}{{k}_{{{{{{\rm{B}}}}}}}T}\right)\), where E_a is the activation energy for the motions and k_B is the Boltzmann constant. Inset shows Q dependences of the Γ. e, f Experimental EISF compared with different reorientation models at 260 and 300 K, respectively. Insets show the schematic diagrams of the coordinations between I⁻ and [NH₄]⁺ ions in the β- and α-phases, respectively. Following the symmetric operations, the hydrogen atoms could dwell on any of the diagonal lines in the β-phases, while the hydrogen atoms residing along the [100] direction would give a sixfold steric distribution in the α-phase (single-approach model, see Supplementary Fig. 6).