抄録
The nuclear spin relaxation times T1 and T1ρ for Na in doped NaCl crystals, along the static and rf field, respectively, have been measured below 110°C to study slow thermal motion of the bound positive ion vacancy around the divalent impurity ions Cd++, Ca++, and Sr++ Below 110°C almost all vacancies form complexes with divalent ions. Slichter’s formula for T1ρ is applicable to the present case where the electric quadrupole interaction determines the local field. Activation energies for the jump of a vacancy in a nearest-neighbor Na site to a next nearest-neighbor site have been measured accurately; 0.64±0.03 eV for NaCl:Cd, 0.71±0.05 eV for NaCl:Ca, and 0.74±0.03 eV for NaCl:Sr. These values agree with the results of dielectric relaxation and ionic thermocurrent measurements. Motion of vacancy-impurity dipoles in a higher complex (probably the pentamer) causes complicated temperature dependence of relaxation times in Ca-doped NaCl.
