By measuring the temperature dependence of the nuclear quadrupole splitting of the Tm 169 8.4-keV Mossbauer y transition, a measure of the strength of the crystalline electric field (CEF) in several hexagonal intermetallic compounds of the type TmX 2 , where X is another transition element, has been obtained. As in thulium metal, a zero-order model of the CEF incorporating only the C2 0 parameter is found sufficient to describe the experimental results. On this basis, the over-all CEF splitting of the Z HQ ground term of the Tm 3+ ion is found to be 94 cm" 1 in TmRu 2 , 88 cm -1 in TmRe 2 , and 42 cm -1 in TmMn 2 . The nuclear and ionic shielding parameters RQ and

Proton, deuterium, and sodium-23 nuclear magnetic resonances of deuterated and ordinary lecontite have been studied from 77° to 300°K and particularly in the vicinity of the ferroelectric phase transitions at 92° and 101°K. Proton–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 230°K the deuterium magnetic resonance of one type of water molecule is observed in the 180° flip state of motion. Below 101°K axial and equatorial deuterons of ND4+ groups rotating about the threefold axis are observed with no detectable change at the transition temperatures. At 300°K one kind of 23Na site is observed; below 101°K, 23Na satellite line splitting occurs indicating that there are two kinds of 23Na site in the unit cell. This splitting is attributed to an abrupt lattice distortion which occurs as the crystal is cooled below 101°K. Proton spin–lattice relaxation time data show two minima, one at 170°K and one at 120°K, which are, respectively, assigned to rotation about the twofold and threefold axes of the NH4+ tetrahedron. Rotating frame relaxation times show minima at 80°, 110°, and 210°K, respectively, due to the threefold and twofold axis rotations of the NH4+ ion and a 180°, flip motion of one kind of H2O molecule. Near 101°K the activation energy for the threefold axis rotation of the NH4+ ion changes from 2.0 to 3.1 kcal mole−1. It is proposed on the basis of the magnetic resonance data that the transition at 101°K in lecontite is of the displacive type with a relatively large lattice distortion.

Proton relaxation times, second moments, and deuteron line splittings have been measured in the solid phases of HCl, HBr, and HI from 50° to 200°K. In solid I of each hydrogen halide two types of molecular motion have been detected: (1) a rapid rotational reorientation and (2) translational diffusion of the molecules. Solid III of HBr shows an intermediate plateau in the proton second moment and both HBr and HI have a well-defined minimum in the rotating-frame relaxation time T1ρ. These effects are interpreted as due to a single-plane reorientation process. Similar minima of T1ρ are observed in solid II of HI and the intermediate solid of HBr, which are ascribed to two-plane and three-plane reorientation processes. The splitting of the deuteron resonance of DBr and DI is quite dependent on temperature but not as strongly dependent as expected for equal site occupational probability. It is proposed that in the ferroelectric solid II of HCl the molecules undergo a single-plane reorientation process but with nonequal orientational site probabilities. Correlation times for these motions are compared with correlation times derived from dielectric loss measurements. The two sets of correlation time data are generally in order-of-magnitude agreement.

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The continuous-wave deuteron magnetic resonance of ND4D2PO4 (ADP) was investigated above and below the antiferroelectric phase transition temperature (228°K). Principal coordinate systems of the deuteron-electric field gradient tensor were determined. A large line splitting occurs below T e owing to the localization of deuterons on phosphate tetrahedra. Smaller line splittings also occur which are due to distortions of the OD bond directions. Proton relaxation times of NH4H2PO4 exhibit a minimum at 170°K and a discontinuity near the transition temperature (r c -148°K). The discontinuity is accompanied by a change in activation energy for the NH4 4 * ion reorientation from 3.7 kcal mole"* 1 (T>T C ) to 4.3 kcal mole" 1 (T