Slater Ice Rules and H-Bond Dynamics in KDP-Type Systems

Abstract

We report on the first observation of the dynamics of correlated hydrogen switching among the six Slater D2PO4 configurations, induced by unpaired D3PO4 and DPO4 Takagi group diffusion in a deuteron glass Rb0.5(ND4)0.5D2PO4. The results obtained by two-dimensional (2D) 31P exchange NMR prove the validity of the Slater-Takagi ice rules and allow for the direct determination of the correlation time for the unpaired Takagi group visits to a given D2PO4 group.

Evidence for Ferroelectric Nucleation Centres in the Pseudo-spin Glass System Rb1−x (ND4) x D2PO4: A 87Rb NMR Study

“…In contrast to the pure end members RDP and KDP, the macroscopic strain cannot develop properly in the mixed crystals. In the glass phase regions the system remains pseudo-tetragonal down to very low temperatures, though the local symmetry is "apparently" broken (the system is only pseudo-frozen and restores the symmetry in the long time scale [11,12]). The strain can only develop when the FE clusters, and with them the coherence length of the soft mode, become wide enough.…”

“…Another interesting nucleus is the 31 P that is located in the centre of the PO 4 tetrahedra. Via the chemical shift interaction, 31 P NMR can, for example, distinguish between the six Slater states of its PO 4 group and thus observe changes of these configurations [11,12]. Furthermore, the characteristic time scale of NMR for time averaging is in the order of milliseconds, and can be extended to the order of 100 s by means of 2D exchange NMR measurements.…”

“…There is, however, a non-vanishing probability that the Takagi pair separates into two unpaired Takagi groups that are stable. The existence of unpaired Takagi groups in a KDP-type lattice was proved by means of 31 P two-dimensional (2D) exchange NMR [11,12]. Recently the separation of a Takagi pair in the FE bulk of KDP was beautifully demonstrated by means of ab initio electronic structure calculations [14].…”

“…In the temperature dependence of 87 Rb spin-lattice relaxation we observe essentially two competing mechanisms: a soft mode component related to the displacive part of the FE phase transition and a thermally activated component that can be assigned to the biased random walk of unpaired Takagi groups T1 (HPO 4 ) and T3 (H 3 PO 4 ) [11,12]. They can move through the lattice without essential hindering, similar to the ion states HO -and H 3 O + in hexagonal ice.…”

1H–19F spin–lattice relaxation spectroscopy: Proton tunnelling in the hydrogen bond studied by field-cycling NMR

“…For fundamental investigations of the proton transfer process, solid-state NMR is well-suited to characterising the hydrogen dynamics [3][4][5][6][7]. The role of tunnelling can be a complex one so it is important to investigate model systems to gain fundamental insight into the proton transfer process as well as to provide a platform for a deeper exploration of the experimental protocols used to investigate the dynamics.…”