Isotope effects in paraelectric relaxation

Through measurements of the complex dielectric susceptibility in the temperature range between 0.3°K and a few °K we have studied the influence of the isotopic substitutions H→D and¹⁶O→¹⁸O on the relaxation time of the hydroxyl dipole in weakly doped KBr and RbCl. The H→D effect is present in both host lattices. The oxygen effect, however, is only for RbCl outside experimental error, indicating that in this host lattice the reorientation of the hydroxyl ion involves a considerable displacement of its center of mass.