Aggregation of Point Defects in Highly Doped NaCl:Ca++Crystals

The spin‐lattice relaxation time T1 measured by pulsed nuclear magnetic resonance is determined by the concentration of the Me2+‐cation vacancy dipoles alone contrary to the dielectric loss measurements. Therefore this method is used to investigate isothermal anncaling proceses via the dipole concentration also for long times when higher aggregates are formed. It is found that aggregation processes take place in NaCl: Ca2+ crystals in the range up to 200°C. For higher temperatures no change in the dipole concentration can be measured. Whereas for small doping levels (up to 500 ppm) mainly dimers and trimers are formed, at high concentrations (over 1000 ppm) the formation of the Suzuki like phase is shown and described theoretically. The enthalpy for the dipole motion (0.60 eV) and the dimer association enthalpy (0.31 eV) are calculated analysing the experimental curves.