Internal stress in doped NH4Cl:Mn2+ crystals

Abstract

The relationship of the effect of impurity on crystal growth and morphology, along with the internal stress and anomalous birefringence arising upon impurity trapping by a growing crystal, is considered. The NH4Cl-MnCl2-H2O-CONH3 model system and the heterostructural NH4Cl:Mn2+ crystals formed in it are experimentally studied. It is found that up to 6.63 wt % Mn2+ impurity is effectively captured by growing NH4Cl crystals at an impurity trapping coefficient only slightly below unity. The effect of Mn impurity stabilizes the full-face growth of NH4Cl crystals with a rhombododecahedral habit in aqueous solutions and a cubic habit in water-formamide solutions. The trapping of manganese impurity by ammonium chloride crystals causes high internal stress (up to 4 GPa) in them, which manifests itself in the form of anomalous birefringence and leads to splitting, twinning, and cracking in NH4Cl crystals.