Study of inclusions and growth bands in potassium bichromate crystals grown from aqueous solutions

Abstract

The nature of inclusions and growth bands in potassium bichromato crystals obtained from aqueous solutions and their formation in relation t o growth tomperatare and supcrsaturation are investigated. It is observed that impurities present in solution, fluctiintioiis in growth trmperatiire anti high prowt,h rates arc rrsponsihlc for t>hcir formation.

Investigations of impurity striations in potassium bichromate crystals

“…We can notice that induced striations were generated only when stirring was stopped, but striations were not formed in most sectors, or were generated only occasionally, during intensive stirring of the solution. These results and our earlier observations [6,8,9,14] confirm the opinion that impurity segregation and striations formation are mainly governed by convection currents (e.g. [28]).…”

“…However, to reveal weak lattice strains present at impurity striations in some other sectors such as the (011) and (012)sectors longer etching time is necessary. The presence of various, strong and weak lattice strains at impurity striations is the expected feature of KBC crystals, since our earlier results showed various capture of inclusions [9], and various intensity of growth bands in various sectors by chemical etching and by X-ray topography [6]. The property that the same, fast dislocation etchants reveal growth bands, sector boundaries and dislocations has been established in KBC crystals [9], and it is expected from the theoretical point of view [15].…”

“…The presence of various, strong and weak lattice strains at impurity striations is the expected feature of KBC crystals, since our earlier results showed various capture of inclusions [9], and various intensity of growth bands in various sectors by chemical etching and by X-ray topography [6]. The property that the same, fast dislocation etchants reveal growth bands, sector boundaries and dislocations has been established in KBC crystals [9], and it is expected from the theoretical point of view [15]. Dam and van Enckevort [16], and Sangwal and Owczarek [15] analyzed the mechanisms of formation of etch grooves at planar defects such as impurity striations and growth sector boundaries in crystals grown from solutions.…”

“…Crystal growth was carried out in 2 L round-bottomed flasks on seeds with or without stirring, or in 2 L beakers by self nucleation without stirring. The details of the experimental procedure for crystal growth are described in earlier papers [9,12,13]. In the present work, as in previous our reports, growth temperature of crystals is indicated in parentheses.…”

“…An analysis of spatial distributions of various defects in KBC crystals reveals that inclusions [9], intensive striations ( [9], and this paper) and point-defect clusters are present in the same sectors. Moreover, the local densities of dislocations and densities of point defects clusters are usually one order of magnitude higher in regions of striations, i.e.…”