Behavior of Foreign Ions contained in NaCl Crystals (Part II)
1966 Volume 20 Issue 2 Pages 79-92
Details
1966 Volume 20 Issue 2 Pages 79-92
A study was made on the mechanism of causing the lattice defects by the foreign positive ions contained in NaCl crystals and on the relation between the lattice defects and the transparence of crystals. The following were the results obtained from the above study:
1 It was assumed that the mechanism of causing the lattice defects by the foreign positive ions contained in NaCl crystals was more complicated than is generally considered, Namely, the impurity ions were considered to exert an influence on the thermal lattice vacancies.
2 The density of free positive vacancies caused at a temperature specialized to a respective impurity ion were considered equal to that of pure NaCl crystals. The author called this special temperature an equivlaent-vacancy temperature. In the temperature range lower than the abovementioned temperature, the impurity ions contained restricted the causing of the thermal vacancies, but they promoted it in the higher temperature range on the other hand.
3 Therefore, the constitution of the lattice vacancies in NaCl crystals was considered to differ according to the range of temperatures. Especially, what was worthy of attention was that in the range of lower temperatures the. Cl-vacancies gradually decreased with the gradual increase in impurity ions and they finally became none at a certain content of respective ion.
4 The liquid cavities which provoke an opacity of crystals were understood to be produced in close connection with the form of adsorption layers and steps, i. e. when the adsorption layers are thick or when they are produced very often or when the steps are crooked irregularly, more cavities are enclosed.
5 It was presumed that the deformation of the adsorption layers and steps was caused by the disorder of crystal lattice and that the disorder of crystal lattice occurred only when Cl-vacancies existed in crystals and would not occur even if the Na+vacancies existed.
6 Thus, it may be considered that the Cl-vacancies are the major factor governing the transparence of crystals. The smaller the CI-vacancies become, the more transparent will become the crystals, and the perfect transparency can be accomplished when there exist no Cl-vacancies.
