Glide in CsCl Structure

As mentioned above alkali halide crystals are strongly hardened by small additions of divalent impurities. Data are available for 12 cases, the host crystals NaCl, NaBr, KC1, and KBr with additions of Ca2+, Sr2+, and Ba2+ (Chin, et al., 1973). It was found that the hardness increases depend only on the concentrations of the additions and not on the divalent specie (Ca, Sr, or Ba). However, a dependence on the valence (1, 2, or 3) is observed. It was also found that hardness increment is proportional to the square root of the concentration, (C1/2). 

The observations given above are inconsistent with the model that Chin et al. used to interpret their measurements. This model, known as Fleischer s model, is based on the idea that the ion-ion dipoles formed between divalent 

Before a dislocation on one of the glide planes passes through the complex, the distance between the two charge centers is d = b = a0/ /2. After it has passed by the distance is d = V2(b) = a0. Therefore, if K is the static dielectric constant, and q = electron s charge, the energy difference between the before and after states is AU = (q2/Ka0)(V2-l). 

---