TEMPERATURE-DEPENDENCE OF THE NUCLEAR-QUADRUPOLE RELAXATION RATE IN SILVER AND SODIUM-HALIDE CRYSTALS

The results of the temperature dependence of nuclear relaxation rate, 1/T-1 measured for Na-23, Cl-35 and Br-79 in AgX and NaX with X being Cl and Br are interpreted in terms of the quadrupole relaxation due to lattice vibrations and defect motions. The data of 1/T-1 in the low temperature region are compared with a model calculation based on an ionic model, in which the degree of covalency is estimated. The result is 24.5% in AgBr and 20.5% in AgCl, which are found to be an order of magnitude larger than the Values in sodium halides. On the other hand, from an analysis of 1/T-1 data in the high temperature region, the migration and formation energies of defects are evaluated and compared with the results of previous conductivity measurements. The obtained activation energies for migration are 0.27 eV in AgBr, 0.23 eV in AgCl and 0.60 eV in NaCl.