Mixed-cation effect in a superprotonic phase of [(NH4)1−xRbx]3H(SO4)2 studied by 1H solid-state NMR

Proton diffusion in the superprotonic phase of [(NH4)1−xRbx]3H(SO4)2 as studied by 1H spin-lattice relaxation

“…The spin-lattice relaxation time is sensitive to a motion with a rate comparable to the measuring frequency, that is, about 200 or 20 MHz in the present work. 13 MHz consist of two components; acidic protons and ammonium protons [21,22]. Proton exchange between the acidic protons and the ammonium ions is slow.…”

“…In the previous works, dynamic behavior in [(NH 4 ) 1 − x Rb x ] 3 H (SO 4 ) 2 (0 b x b 1) was studied extensively [22] as well as those in (NH 4 ) 3 H(SO 4 ) 2 [11] and Rb 3 H(SO 4 ) 2 [10]. In all the phases, very fast isotropic reorientation of NH 4 + ions takes place.…”

“…The 1 H static NMR spectra indicate that both NH 4 + ions and the acidic protons undergo translational diffusion [22]. From the analysis of 1 H T 1 results we have obtained parameters for the translational diffusion of the acidic protons, as listed in [19].…”

“…In the previous works, we have studied proton dynamics in [21,22]. We have measured and analyzed 1 H MAS NMR spectra and NMR spectra for static samples (static NMR spectra) as well as X-ray powder diffraction and thermal analyses.…”

“…As a result, we have obtained the diffusion rate of protons in phase I and have estimated the proton conductivity rather quantitatively from a microscopic viewpoint. [21,22]. They were grown by slow evaporation of the aqueous solution containing stoichiometric amounts of (NH 4 ) 2 SO 4 , Rb 2 SO 4 and H 2 SO 4 .…”