Adsorption mechanism of defectiveness in crystal growth

摘要

Correlation between the specific adsorption ofimpurity by crystal faces and formation of autodeformation defectswas studied within the system K_2SO_4—K_2WO_4—H_2O.Adsorption of polywolframat-ions on the (010) faces ofK_2SO_4crystals leads to drastic modification of crystal habit.Behaviour of crystal anisometry follows the Bliznakov—Chernovequation. It proves that the impurity hinders the growth of (010)faces poisoning the kink sites on growth steps. The adsorption ofimpurity induces the curved-faces growth of K_2SO_4 crystalsand stimulates sites on growth steps. The adsorption of impurityinduces the curved-faces growth of K_2SO-4 crystals andstimulates the formation of growth twins and the by the low rate ofsubunit multiplication. Thus, main consequence of impurityadsorption is its nonisomorphous trapping in crystal, that in itsturn causes the local inner stresses. Increase of the growth rateanisotropy increases the probability of subunit autonomization.This mechanism stimulates linear developmetn as anisotropyincreases the probability of subunit autonomization. Thismechanism stimulates linear development as well as the growthtwinning of crystals. In the latter case it influences also themorphology of twins. The same effect has been found for NaNO_3crystals growing in the presence of (NH_4)_2MoO_4 as well asfor natural plagioclase crystals from volcanic rocks of Kamchatka.Adsorption stimulation of twinning and splitting of crystalsexplains the well-known empirical correlation between theintensity of defecteness and the crystal habit of minerals.