133Cs Spin-Lattice Relaxation and Resonance in Ferroelectric CsD2AsO4 and CsH2AsO4

The electric field gradient (EFG) tensor at the Cs sites in CsH₂AsO₄ and the ¹³³Cs spin‐lattice relaxation rate in CsD₂AsO₄ have been determined. The results show that the time averaged value of the EFG tensor at the Cs site in the paraelectric phase is the average of the two ferroelectric EFG tensors for opposite directions of polarization, and that the time dependence of the Cs EFG fluctuations is determined by the same dynamic process which governs the EFG fluctuations at the deuteron sites in the $\mathrm{O}–\mathrm{D}\mathrm{···}\mathrm{O}$ bonds.