Proton, deuterium, and sodiumhyphen;23 nuclear magnetic resonances of deuterated and ordinary lecontite have been studied from 77deg; to 300deg;K and particularly in the vicinity of the ferroelectric phase transitions at 92deg; and 101deg;K. Protonndash;proton vector directions were determined for the two kinds of water molecules in the unit cell and are observed not to alter as the phase transitions are traversed. Above 230deg;K the deuterium magnetic resonance of one type of water molecule is observed in the 180deg; flip state of motion. Below 101deg;K axial and equatorial deuterons of ND4plus;groups rotating about the threefold axis are observed with no detectable change at the transition temperatures. At 300deg;K one kind of23Na site is observed; below 101deg;K,23Na satellite line splitting occurs indicating that there are two kinds of23Na site in the unit cell. This splitting is attributed to an abrupt lattice distortion which occurs as the crystal is cooled below 101deg;K. Proton spinndash;lattice relaxation time data show two minima, one at 170deg;K and one at 120deg;K, which are, respectively, assigned to rotation about the twofold and threefold axes of the NH4plus;tetrahedron. Rotating frame relaxation times show minima at 80deg;, 110deg;, and 210deg;K, respectively, due to the threefold and twofold axis rotations of the NH4plus;ion and a 180deg;, flip motion of one kind of H2O molecule. Near 101deg;K the activation energy for the threefold axis rotation of the NH4plus;ion changes from 2.0 to 3.1 kcal moleminus;1. It is proposed on the basis of the magnetic resonance data that the transition at 101deg;K in lecontite is of the displacive type with a relatively large lattice distortion.
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