Proton dynamics of CsH2PO4 studied by quasi-elastic neutron scattering and PFG-NMR

To illuminate ionic conduction behavior of super protonic phase of CsH2PO4 (CDP), quasi-elastic neutron scattering (QENS), pulse field gradient nuclear magnetic resonance (PFG-NMR) and 1H NMR spin-lattice relaxation time (T1) measurements were carried out. Diffusion coefficient of protons obtained from PFG-NMR reproduced well the electrical conductivity by using Nernst–Einstein equation. Comparison of PFG-NMR and T1 provided a hopping distance of protons as 2.7 Å, which agreed with the next nearest proton sites in CDP. On the other hand, QENS data was fitted well with a jump-diffusion model. Comparison of the jump diffusion coefficient and the correlation time obtained by QENS provided a librational correlation time of protons in the order of 10− 12 s. The present investigation suggests that different techniques, QENS and NMR, can observe protonic motions having different time constants including librational and translational motions within the hydrogen bonding network of CDP.