Transport of Matter in Simple Ionic Crystals (Cubic Halides)

Aggregation of divalent metal impurity in alkali halide crystals

As part of a study of the aggregation of impurity ions in alkali halides, measurements of dielectric loss, of optical absorption and of emission spectra have been made on NaCl: Pb2+ and KCl: Pb2+ crystals. Changes in the optical absorption and the emission spectra with aggregation of the Pb2+-vacancy pairs are more pronounced in NaCl than in KCl. The main conclusions from the NaCl: Pb2+ measurements are: changes in the absorption and emission spectra result from the same aggregation process studied previously in many alkali halide crystals by dielectric measurements; the emission spectra, but not the absorption, change when the divalent ion-vacancy pairs (dipoles) form the initial aggregates (trimers); later in the aggregation process both absorption and emission change; the optical measurements show that the aggregation takes place in several definite stages and the results are not inconsistent with the model proposed earlier, viz. the initial aggregates are trimers and these grow into pentamers, and then heptamers etc. by the addition of dipoles, two at a time. The dielectric absorption measurements give activation energies for the diffusion of Pb2+-vacancy pairs through NaCl and KCl lattices of 080 ev and 085 ev respectively.

https://iopscience.iop.org/article/10.1088/0022-3719/2/4/305/pdf

Dielectric and optical properties of lead-activated sodium and potassium chloride crystals

Impurity precipitation in alkali halide crystals

A theoretical study of alkaline-earth cations in crystalline sodium chloride, potassium chloride and potassium bromide

Etch pits of KCl crystals obtained with dehydrated glacial acetic acid were observed. KCl is so soft, comparing with LiF, that dislocations are generated on it by slight mechanical shocks. Therefore, surfaces of KCl crystal are apt to be contaminated in the sense of the dislocation theory. It is supposed its depth usually reaches 100 µ or more and also most of these generated dislocations are surface half loops and isolated loops. One to one correspondence between etch pits and dislocations is discussed.

One to One Correspondence between Etch Pits and Dislocations in KCl Crystals

Aggregation Process of Dipoles in Ca Doped KCl Crystals

The Effect of Hydroxide on the Aggregation of Dipoles in Sr-Doped KCl Crystals

Time-Dependent Internal Friction in Deformed NaCl Crystals

Effects of thermal quenching on KCl crystals were studied in both clear and colored specimens. These were subjected to two types of quenching, down- and up-quenching. The etching method was carried out to examine generated dislocations and the photoelastic method was used to see the distribution of the residual stresses. The results of the experiments are as follows: (1) Generated dislocations, distributing from the crystal surface toward the interior, were perceived. (2) They ranged over a lunar area along the edges in the cross section of the specimen. (3) The range, in which the residual stresses exist, has also the same lunar form along the edges. Therefore, the residual stresses are considered as resulting from the thermal generation of slips. These experimental facts can be explained on the basis of thermal stresses.

Masayoshi Sakamoto

Papers

One to One Correspondence between Etch Pits and Dislocations in KCl Crystals

Aggregation Process of Dipoles in Ca Doped KCl Crystals

The Effect of Hydroxide on the Aggregation of Dipoles in Sr-Doped KCl Crystals

Time-Dependent Internal Friction in Deformed NaCl Crystals

Quenching Effect in KCl Crystals