A deuterium NMR study of D(UO2XO4), 4D2O; X = P,As

Deuterium NMR spectra have been obtained by the solid echo technique for polycrystalline samples of DUO₂XO₄, 4D₂O, with X = P (DUP) and As (DUAs). Transitions (II → I) were found, by DSC measurements, to occur at 260 and 290 K for DUP and DUAs, respectively. In the high temperature tetragonal phase I, the NMR lineshapes are consistent with motionally averaged axially symmetric electric field gradient tensors, with values for $\text{〈}\text{e}{}^2\text{qQ}\text{h}\text{〉}{}_{\mathrm{<mtext>av</mtext>}}$ of 39.2 ± 0.2 and 38.2 ± 0.2 kHz for DUP and DUAs, respectively. This requires fast chemical exchange of the deuterium atoms between all of the hydrogen-bond sites in a water layer, and participation of all of the deuterium atoms in the diffusion process. There are no discernible discontinuities in the spectra at the transition temperature suggesting that there is little change in the local structure of the water layers at the transition. The spectra disappeared at about 10 K below T_c and for DUP a distorted broader spectrum became discernible below about 200 K.