Monte Carlo simulation of NMR line shapes in distorted non-metallic solids

The Monte Carlo method is applied to calculate the quadrupole distortion of the shape of the NMR spin echo signal caused by randomly placed defects (points defects or dislocations) in a cubic lattice. Specific evaluations are carried out in the case of 23NaCl and 23NaBr disturbed by Ca2+ (valence effect), by Ag+ (strian effect), and by a defined number of dislocations, respectively. The theoretical results are compared with NMR measurements on 23NaCl and 23NaBr single crystals distorted by 0.01 at% Ca2+, 0.5 at% Ag+, 6x107 dislocations/cm2, and 1.8x108 dislocations/cm2, respectively. It is found that the calculations agree well with the experimental data in the case of doped crystals, whereas some deviations between measurements and theory exist if the crystal is strained by dislocations. These discrepancies may be explained by a non-uniform distribution of the dislocations in the crystal. (author)