Symmetry change of 77Se hyperfine components of ESR spectrum of SeO43- radicals in deuterated NH4H2PO4

D-rate dependence (0 - 70 %) of the 77Se hf line-positions of SeO43- radicals in deuterated NH4H2PO4 is reported. In the paraelectric phase, on cooling, the symmetry of the angular dependence changes from high symmetry to low-symmetry A (which is similar to that for KDP or DKDP), but no remarkable deuteration effect is observed. In the antiferroelectric phase, the angular dependence for ADP still shows the low-symmetry A, while that for DADP (D70 %) shows the low-symmetry B which is compatible with the AFE order (the Nagamiya's model) of the ammonium salts. From this large deuteration effect on the SeO43- it is suggested that the AFE distortion of the PO43- radical in the D salts is larger than that in the H salts. (author)