Dynamical Effects of Deuteron Intrabond Jumping in KD2PO4

Deuteron jumps along hydrogen bonds in K${\mathrm{D}}_2$P${\mathrm{O}}_4$ associated with effective motion of Slater-Takagi DP${\mathrm{O}}_4$ and ${\mathrm{D}}_3$P${\mathrm{O}}_4$ groups are related to the deuteron magnetic-resonance spectrum and relaxation both above and below the ferroelectric transition temperature $T_c$, and to the dielectric relaxation and the domain-wall mobility. Below $T_c$ the deuterons assume ordered bond positions, but occasionally jump to the opposite positions. The correlation time for the electric-field-gradient fluctuations seen by a deuteron undergoing such motion is found to be short above $T_c$ and even shorter below $T_c$. The rms amplitude of the fluctuations drops rapidly below $T_c$. These results are used to explain the temperature dependence of the splitting and lack of line broadening in the deuteron spectrum below $T_c$, and the rapid decrease of the spin-lattice transition probabilities below $T_c$. Relaxation data above $T_c$, which yielded the energies and fractional populations of DP${\mathrm{O}}_4$ and ${\mathrm{D}}_3$P${\mathrm{O}}_4$ groups, are reanalyzed using the recently reported field-gradient tensors at the two bond positions. The dielectric relaxation is calculated, and good agreement with the high dielectric loss measured at microwave frequencies is found. The jump time for a DP${\mathrm{O}}_4$ or ${\mathrm{D}}_3$P${\mathrm{O}}_4$ group is found to be near $\frac{h}{\mathrm{kT}}$, implying little correlation between successive jumps, in contrast to K${\mathrm{H}}_2$P${\mathrm{O}}_4$. This jump time is used in a calculation of domain-wall mobility in K${\mathrm{D}}_2$P${\mathrm{O}}_4$.