Influence of diffusion on the morphology of NaCl crystals grown from the vapor phase

Abstract NaCl crystals were grown from the vapor phase in a sealed quartz vessel on a fused quartz substrate. Under a wide variety of growth conditions, the crystals grew in a cubic or mosaic form. At temperatures around 600°C in a vacuum of 10 -5 Torr or in an Ar atmosphere at pressures lower than 1 Torr, however, polycrystals grew in the form of planar convex lens. When a cubic shaped crystal was used as the seed, the cube changed to a star-like shape at 600°C as a result of growth from the corner at a supersaturation above the critical value of σ c = 80%. The parts growing from the corner were polycrystals which extended to the quartz substrate. The growth proceeds by nucleation in random orientations around the corner, where the supersaturation is higher than in the middle of the crystal edge in the two-dimensional diffusion field on the substrate around a growing crystal. This shows evidence of the Berg effect in the case of growth from the vapor phase.