Pressure dependence of bound-vacancy motion in doped NaCl

Abstract

The effect of pressure to 6 kbar on the nuclear-magnetic-resonance rotating-frame relaxation time $T_{1\rho }$ in doped NaCl is studied at temperatures near 100 °C. Cation vacancies are almost all associated with the added divalent impurities ${\mathrm{Cd}}^{2+}$, ${\mathrm{Mn}}^{2+}$, and ${\mathrm{Hg}}^{2+}$ at these temperatures. The jumping of these bound vacancies among sites nearest and next nearest to the impurities causes relaxation of the nuclear magnetization. From the pressure dependence of the rate of relaxation, the activation volume for this motion is found to be 7.4 ± 1 ${\mathrm{cm}}^3$/mole, comparable to the value for free-vacancy motion. There is a contribution to the total activation volume from the volume of solubility or precipitation (${\nu }_s=3.5\mathrm{}\pm 2$ ${\mathrm{cm}}^3$/mole) in the Cd- and Mn-doped samples, but not in the Hg-doped sample.