Study of the structural phase transitions in Na3D0.51H0.49(SO4)2 crystals by 2H and 23Na nuclear magnetic resonance

The mixed Na3DxH1−x(SO4)2 crystals grown in this study have a deuterium fraction of 51%, and the phase transitions for Na3D0.51H0.49(SO4)2 were found to occur at 300 K ( = T C 1 ) and 546 K ( = T C 2 ) . The NMR spectra and the relaxation times of 2H and 23Na in Na3D0.51H0.49(SO4)2 crystals were measured as functions of temperature. Although our results for the 2H and 23Na relaxation times provided no evidence of the phase transitions at T C 1 , the 2H and 23Na NMR spectra did change. The phase transitions at 300 K produced changes in the 2H and 23Na NMR spectra that are associated with changes in the atomic positions of the 2H and 23Na ions. The effects of partial deuteration of Na3H(SO4)2 crystals include not only a shift in the phase transition temperature T C but also a change in the local symmetry.