NMR Studies of Motions in Solids: 1. Motional Narrowing in Adamantane. NonExponential Relaxation of FLUORINE19 in the FastIonic Conductor LeadFluoride
Abstract
The translational motion of molecules in the plastic crystal phase of adamantane is studied using the technique of motional narrowing. A systematic measurement of free induction decays (fids) was made in the moderate narrowing region of the absorption line and the motional parameters such as activation energy and jump frequency are determined from them. A general calculation for the coefficients of the power series expansion of these fids, using a technique similar to the Van Vleck method of moments, is presented. The spatial variables are treated as classical stochastic Markov variables. A relationship between one of the momentlike expansion coefficients and the spinlattice relaxation time in the rotating frame is established. In addition, an integral equation is derived to describe the long time behavior of the narrowing process. The spinlattice relaxation technique is used to study the ionic motion in fastionic conductor (beta) PbF(,2) doped with monovalent cations. The relaxation time T(,1r) measured as a function of temperature and rotating magnetic field shows anomalous behavior. In this work, the nonexponential decay of the spinlocked magnetization is explained by proposing a nonuniform distribution of the dopant ions. A phenomenological model is used to describe the probability density distribution of a vacancy around a dopant center. The resulting expression fits the spin locked magnetization decay data very well.
 Publication:

Ph.D. Thesis
 Pub Date:
 1985
 Bibcode:
 1985PhDT........82P
 Keywords:

 Physics: Condensed Matter