The precipitation of the cubic Suzuki phase in NaCl: Cd2+and NaCl: Mg2+

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Abstract
Low-temperature transmission electron microscopy wm used to observe directly Suzuki precipitates in single crystals of NaCl: Cd2+ and NaCl: Mg2+. An accelerating voltage of 1000 kV and low beam current densities of the order of 3 Am−2 were used in addition to low temperatures to retard radiation damage to the specimens. Slowly cooled, annealed and quenched specimens of several Cd concentrations were examined and their precipitation sequences compared with the position of the solvus obtained by other techniques. The effect of increasing the Cd concentration on the morphology and coherency of the precipitates was also observed and related to other studies. Matrix dislocations and dislocations arising from the presence of the precipitates were seen and their possible origins and main features are discussed. At the higher doping levels, transformation of the 〈100〉 faces of some of the precipitates takes place. The interfacial dislocation spacing in NaCl: Mg2+ was found to agree with previously calculated values for perfect1/2a〈110〉 dislocations, rather than with complex partial interfacial dislocations, Measurements of ionic conductivity were carried out on NaCl: Cd2+ specimens helonging to the same platelets as those used in the T.E.M. experiments. The analysis developed by Guerrero, Jain and Pratt (1978) was extended to include precipitation and was applied to the ionic conductivity data. The results were correlated with the T.E.M. observations and yielded a value 0·40 ± 0±03 eV for the binding energy of Cd-vacancy dimers.