Interferometric Study of the Stability of K2CoxNi(1−x)(SO4)2·6H2O (KCNSH) Mixed Crystal Faces Depending on the Composition and Flow Velocity of the Solution

В В Гребенев ,S I Kovalyov ,N A Vasilyeva ,Е Б Руднева ,M S Lyasnikova ,В Л Маноменова ,А Э Волошин

doi:10.3390/cryst10121112

Abstract

The change in the surface morphology of the (001) and (110) faces of K2CoxNi(1−x)(SO4)2·6H2O (KCNSH) mixed crystal, depending on the supercooling solution, has been studied under various conditions by laser interferometry. The experiments were carried out in both static mode, by changing the solution composition, and in dynamic mode, by changing the flow velocity. The conditions for the onset and suppression of the reaction of the isomorphic replacement leading to the formation of mosaic micro-inhomogeneity in mixed crystals have been studied. The mechanism of the reaction of isomorphic replacement has been analyzed depending on the shift of the solution composition from the initial one. For the first time, it has been observed that the reaction of isomorphic replacement may occur through a layer-by-layer mechanism.

Highlights

Mixed crystals K2 Cox Ni(1−x) (SO4 )2 ·6H2 O (KCNSH) are a promising material for UV optical filters for solar-blind technology
The stability of the KCNSH crystal surface to local exchange processes was studied by laser interferometry in the static mode for contact with “foreign” solutions, and in the dynamic mode when the velocity of the solution changes
In static mode, when the composition of the salt mass of the solution shifts from the initial one by 17 and 25 wt.%, the processes of crystal dissolution and the growth of a new phase begin at the top of the vicinal hillocks and occur layer-by-layer

Summary

Introduction

Mixed crystals K2 Cox Ni(1−x) (SO4 )2 ·6H2 O (KCNSH) are a promising material for UV optical filters for solar-blind technology. In [3,4], a set of measures has been described that make it possible to suppress these types of inhomogeneities (growing crystals in shapers, at a constant temperature, and with supercooling, with solution feeding according to a special law). This resulted in a significant improvement in the structural perfection of the KCNSH crystals; it was not possible to completely eliminate their increased fragility. The probable reason for this failure is the peculiarities of the processes of the formation of mixed crystals, which cannot be fully described from the standpoint of the classical theory of crystal growth

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