Growth of the tetrahedral faces of sodium chlorate crystals in the presence of dithionate impurity

Abstract

It has been established that trace amounts of S 2O 2- 6 anions initiate the appearance of new faces, { 111 }, on sodium chlorate crystals grown from aqueous solution. The present study compares the growth mechanisms of the {111} habit faces and { 111 } type faces using laser interferometry techniques. The {111} faces show dislocation layer growth in which the impurity influences the growth by causing the gradual deceleration of step movement. In contrast, the { 111 } faces incorporate crystal units into an atomically rough surface. Under these circumstances the impurity on the surface creates a barrier to continuous growth. The strong impurity interaction with the { 111 } faces can be explained by the close structural similarity of the -SO 3 portion of the S 2O 2- 6 ions to the ClO - 3 ions situated on these faces. This allows the dithionate ion to substitute for ClO - 3, disturbing the structure and energy of the interface and inhibiting growth.