Morphology of crystal growth during III phase transformation in K0.945Rb0.055NO3 monocrystal

Summary: K0,945Rb0,055NO3 monocrystals were grown from aqueous solutions of KNO3 and RbNO3 by isothermal crystallization method and the morphology of crystal growth during III phase transformations in these crystals was studied by optical microscopy. It was determined that two polymorphic transformations occur in the studied crystal from room temperature to the melting temperature. The structural transformations in these crystals are enantiotropic and of the monocrystal-monocrystal type. The equilibrium temperature between the interconverting II and I modifications is T=4550.5K. In the investigated sample, a repeated III phase transformation was studied, and the growth of the process was observed in a mono-nucleated manner in the 001 crystallographic direction. This transformation was accompanied by the movement of the non-linear boundary separating the phases. The transformation rate is as 〖2−????[001]>1−????[001]. Experiments show that the rhombohedral modification existing between modifications I and II in potassium nitrate is not detected in the studied sample. Partial replacement of K+ ions with Rb+ ions increases the equilibrium temperature between modifica-tions II and I by about 55 K.