The paraelectric and antiferroelectric phases of Rb3D(SO4)(2) and Rb3H(SO4)
(2) were investigated using rubidium NMR. The angle dependence of the secon
d order quadrupole shifted central Rb-87 transitions was recorded at 300 K.
It was found to be in full agreement with the symmetry elements of a monoc
linic A2/a structure. The temperature dependence of the magnitude and asymm
etry of the electrical field gradient (EFG) tensors at the Rb sites was det
ermined using powder samples and revealed no differences, between protonate
d and deuterated specimens. The antiferroelectric transition of Rb3D(SO4)(2
) (T-N=82 K) is associated with a quadrupling of the unit cell. Below T-N t
he magnitudes of the EFG at the Rb sites remain constant and smoothly tilt
away from their high temperature orientations. The temperature dependence,o
f the NMR line splittings associated with this tilt follows a power law imp
lying an order parameter critical exponent of 0.21. [S0163-1829(99)07517-7]
.